Field of the Invention
The present invention relates to a two-wire load
control device connected in series between a commercial AC
power source and a load such as an illumination apparatus
and motor.
Background of the Invention
Conventionally, a load control device using a non-
contact switch element such as a triac or thyristor has been
practically used (see, e.g., Patent document 1). In terms
of reduction of wires, the load control device generally has
a two-wire connection which is connected in series between a
commercial AC power source and a load. In the load control
device connected in series between the commercial AC power
source and the load, how to ensure power for its circuit
becomes an issue.
As shown in FIG. 43, a load control device 50 of a
first conventional example connected in series between a
commercial AC power source 2 and a load 3 includes a main
switching unit 51, a rectifying unit 52, a control unit 53,
a first power supply unit 54 which supplies a stable power
to the control unit 53, a second power supply unit 55 which
supplies power to the first power supply unit 54 when no

power is supplied to the load 3, and a third power supply
unit 56 which supplies power to the first power supply unit
54 when power is supplied to the load 3. The load control
device 50 further includes an auxiliary switching unit 57
which allows a micro-current from the load current to flow
therethrough and supplies to a gate of the main switch
element a sufficient amount of the current to put a main
switch element 51a of the main switching unit 51 in a
conducting state, and the like. The main switch element 51a
of the main switching unit 51 includes a triac.
In an OFF state of the load control device 50 in which
no power is supplied to the load 3, a voltage applied from
the commercial AC power source 2 to the load control device
50 is supplied to the second power supply unit 55 via the
rectifying unit 52. The second power supply unit 55 is a
constant voltage circuit including a resistor and a Zener
diode 55a. In an OFF state of the load 3, a ripple current
that is full-wave rectified by the rectifying unit 52 is
inputted to the second power supply unit 55 and when a
voltage applied thereto is higher than a Zener voltage of
the Zener diode 55a, the Zener voltage is inputted to the
first power supply unit 54. If the voltage is lower than
the Zener voltage, a buffer capacitor 54a connected between
input terminals of the first power supply unit 54 serves as
a power source for the first power supply unit 54. The
buffer capacitor 54a is repeatedly charged and discharged.

Further, in this case, the current flowing through the load
3 is a micro-current small enough not to cause a malfunction
in the load 3. It is configured such that the current
consumption of the control unit 53 is small and the
impedance of the second power supply unit 55 is set to be
maintained high.
On the other hand, in an ON state of the load control
device 50 in which power is supplied to the load 3, the
third power supply unit 56 is turned on by a control signal
transmitted from the control unit 53, and the impedance of
the load control device 50 is reduced to thereby increase an
amount of the current flowing in the load 3. At the same
time, the current flowing in the third power supply unit 56
also flows in the first power supply unit 54, thereby
starting to charge the buffer capacitor 54a. If the
charging voltage of the buffer capacitor 54a is higher than
a predetermined threshold, a Zener diode 56a included in the
third power supply unit 56 breaks down and the current
begins to flow. The current flows into the gate of the
auxiliary switching unit 57 and the auxiliary switching unit
57 turns into a conducting state (closed state).
As a result, the current flowing into the third power
supply unit 56 from the rectifying unit 52 is commutated to
the auxiliary switching unit 57. Further, the current flows
into the gate of the main switch element 51a of the main
switching unit 51 as well and the main switching unit 51

turns into a conducting state (closed state) . Therefore,
almost all power is supplied to the load 3.
Hereinafter, a case where when the load 3 is in an ON
state, power is supplied to the first power supply unit 54
not from the second power supply unit 55, but only from the
third power supply unit 56 will be described. When a
manipulation switch (SW) 4 for starting the load 3 is turned
on, the control unit 53 outputs a control signal to thereby
put a switch element 56c of the third power supply unit 56
in a conducting state. In this case, since an input voltage
of the first power supply unit 54 serving as an output
voltage of the second power supply unit 55 is higher than an
output voltage of the third power supply unit 56, the
current flowing in the third power supply unit 56
sequentially passes through the Zener diode 56a, a thyristor
57a of the auxiliary switching unit 57, and a triac 51a of
the main switching unit 51. When the triac 51a is in an ON
state, the rectified voltage of the rectifying unit 52
becomes almost zero. Accordingly, the second power supply
unit 55 is turned into a non-conducting state, and there is
no current to flow therein. Also, the third power supply
unit 5 6 is operated in the same way. In the mean time,
since power is supplied to the first power supply unit 54
from the buffer capacitor 54a, the input voltage of the
first power supply unit 54, i.e., the terminal voltage of
the buffer capacitor 54a is reduced gradually. Further,

when the input voltage of the first power supply unit 54
becomes lower than the output voltage of the third power
supply unit 56, the third power supply unit 56 starts the
supply of power to the first power supply unit 54. In this
case, since the Zener voltage of the Zener diode 55a of the
second power supply unit 55 is higher than the Zener voltage
of the Zener diode 56a of the third power supply unit 56,
the second power supply unit 55 remains to be still in a
non-conducting state. Further, the buffer capacitor 54a is
charged such that the terminal voltage thereof becomes the
output voltage of the third power supply unit 56. If the
rectified voltage of the rectifying unit 52 is higher than
the Zener voltage of the Zener diode 55a of the second power
supply unit 55, the input voltage of the first power supply
unit 54 becomes the output voltage of the second power
supply unit 55, but at that moment, the current flowing in
the third power supply unit 56 is commutated to the Zener
diode 56a, the thyristor 57a, and the triac 51a of the main
switching unit 51. By repeating these operations, when the
load 3 is in an ON state, power is supplied to the first
power supply unit 54, not from the second power supply unit
55, but only from the third power supply unit 56.
Once the main switching unit 51 turns into a
conducting state (closed state), the current continuously
flows therethrough. However, when AC current reaches a
zero-cross point, the main switch element 51a is subjected

to a self-arc-extinction and the main switching unit 51
turns into a non-conducting state (open state) . When the
main switching unit 51 turns into a non-conducting state
(open state), the current again flows into the first power
supply unit 54 from the rectifying unit 52 through the third
power supply unit 56, and an operation for ensuring the
power for the circuit of the load control device 50 is
performed. That is, a self power reserve for the circuit of
the load control device 50, a conducting operation of the
auxiliary switching unit 57 and a conducting operation of
the main switching unit 51 are repeated every half cycle of
AC current.
A load control device 60 of a second conventional
example, which is connected in series between the
alternating current (AC) power source 2 and the load 3, is
shown in FIG. 44. The load control device 60 includes a
main switching unit 61, a rectifying unit 62, a control unit
63, a first power supply unit 64 which supplies a stable
power to the control unit 63, a second power supply unit 65
which supplies power to the first power supply unit 64 when
no power is supplied to the load 3, and a third power supply
unit 66 which supplies power to the first power supply unit
64 when power is supplied to the load 3. The load control
device 60 further includes a zero-cross detection unit 67
which detects a zero-cross point of the load current. A
MOSFET is used as a switch element 61a of the main switching

unit 61, and an incandescent lamp serves as a load to be
controlled.
In a case where power is supplied to the load 3, the
switch element 61a of the main switching unit 61 is put in a
conducting state only for a time period determined based on
a dimming level inputted externally. Specifically, the
switch element 61a is put in a conducting state (closed
state) at a timing when the zero-cross detection unit 67
detects the zero-cross point of the voltage, and the switch
element 61a is put in a non-conducting state (open state)
after the time period has elapsed. While the main switching
unit 61 is in a non-conducting state (open state), the power
for the circuit of the load control device 60 is ensured as
in the first conventional example. When the main switching
unit 61 is put in a non-conducting state (open state) , the
zero-cross detection unit 67 detects the zero-cross point
again, and the switch element 61a is put in a conducting
state (closed state). The operation is repeated every half
cycle of alternating current.
However, in the first conventional example, it is
known that a high current (referred to as inrush current)
temporarily flows when power is inputted to the load 3 such
as an illumination apparatus and motor. In the power input,
as described above, since the current flows in the third
power supply unit 56 earlier than conduction of the triac
51a of the main switching unit 51, a high current due to the

inrush current may flow in the third power supply unit 56 or
the auxiliary switching unit 57, thereby causing breakage in
an element forming the third power supply unit 5 6 or the
auxiliary switching unit 57. Further, since the high
current repeatedly flows in the third power supply unit 56
or the auxiliary switching unit 57, the element forming the
third power supply unit 56 or the auxiliary switching unit
57 may be degraded gradually, and the lifetime of the load
control device 50 may be reduced.
As in the load control device 50 of the first
conventional example, in a case where the main switch
element 51a of the main switching unit 51 is a triac or
thyristor, in order to reduce the noise generated when power
is supplied to the load 3, and to prevent a malfunction due
to the noise transmitted from the power source 2 when no
power is supplied to the load 3, it is necessary to provide
a filter. However, it is difficult to achieve
miniaturization of the load control device due to the size
of a coil 58 forming the filter or heating of the coil.
In order to reduce the noise due to the load control
device without using a filter, for example, in a load
control device (third conventional example) disclosed in
Patent document 2, a second switch unit having an on
resistance larger than that of the switch element (first
switch unit) of the main switching unit is provided in
addition to the switch element of the main switching unit

such that after the second switch unit is turned on, the
first switch unit is turned on. However, in the third
conventional example, the number of switch elements becomes
large. Accordingly, a circuit configuration becomes
complicated, and it is also complicated to control the
timing of switch-on.
Further, as in the load control device 60 of the
second conventional example, in a case where the switch
element 61a of the main switching unit 61 has a transistor
structure, the load is limited to a load such as an
incandescent lamp in which the load current and the load
voltage have the same phase (power factor of 1) . Further,
the current is made to flow from the zero-cross point, and
the current is blocked at a phase angle in accordance with
dimming, thereby performing reverse phase control. In this
case, it is necessary to block the electrical conduction
current, causing an increase in the noise. To reduce the
noise, blocking of the current is slowly performed by
controlling the transistor. However, there is a problem in
which heat generated from the switch element increases due
to switching loss generated in blocking.
As in the load control device 50 of the first
conventional example, in a case where the switch element 51a
of the main switching unit 51 has a thyristor structure,
dimming control of the illumination apparatus can be
performed by delaying the conduction of the switch element

51a using a variable resistor. Meanwhile, the triac or
transistor used as the switch element of the main switching
unit is formed of Si, and generally, the current flows in a
vertical direction of the element. In case of the triac,
since there is a PN junction in an electrical conduction
path, loss occurs during the electrical conduction to
overcome the barrier. Further, in case of the transistor,
since it is necessary to connect two elements in a reverse
direction and a low carrier concentration layer being a
withstand voltage maintaining layer has a high resistance,
loss occurs during the electrical conduction. By such loss,
the heat generated from the switch element is large, and a
large heat sink is necessary. Accordingly, it makes it
difficult to achieve miniaturization and high capacity of
the load control device.
Generally, the load control device is housed in a
metal box or the like provided on the wall. However, in the
conventional load control device, because there is a
limitation on miniaturization, the load control device
cannot be used in combination with another sensor, switch or
the like in a box that is generally used nowadays.
Accordingly, in order to install the load control device in
combination with another sensor, switch or the like in a box
with a typical size, there is a demand for further
miniaturization of the load control device.
Further, in the conventional load control device, for

example, in a case where the load is a low capacity load
such as a miniature bulb of the illumination apparatus,
since the main switching unit with large power consumption
is in a conducting state, the power consumed in the load
control device increases and more time is required to charge
a buffer capacitor 59. Accordingly, a time point when the
charging voltage of the buffer capacitor 59 is higher than a
predetermined threshold may exceed the half cycle of the AC
power source, and it is impossible to accurately control an
on/off timing of the main switching unit. Thus, it may
cause a variation in the operation of the load.
Patent document 1: Japanese Patent Application
Publication No. 2007-174409
Patent document 2: Japanese Patent Application
Publication No. 2006-92859
Summary of the Invention
In view of the above, the present invention provides a
load control device capable of preventing breakage or
degradation of an element due to an inrush current generated
when power is supplied to a load.
The present invention also provides a load control
device for performing load control capable of reducing the
number of switch elements, suppressing heat generation in
switch elements to promote miniaturization, accurately

controlling switching timing, reducing power consumption,
preventing a fluctuation, and enhancing lighting control and
the like.
In accordance with a first aspect of the present
invention, there is provided a two-wire load control device
connected in series between an alternating current (AC)
power source and a load, including: a main switching unit
which has a main switch element connected in series to the
AC power source and the load, and controls a supply of power
to the load; a manipulation switch which is manipulated by a
user, and outputs a start-up signal for starting at least
the load; a control unit which is connected to the
manipulation switch and controls opening/closing of the main
switching unit based on a signal transmitted from the
manipulation switch; a first power supply unit, to which
power is supplied from both terminals of the main switching
unit through a rectifying unit, for supplying a stable
voltage to the control unit; a second power supply unit, to
which power is supplied from both terminals of the main
switching unit through the rectifying unit, for supplying
power to the first power supply unit no power is supplied to
the load; and a third power supply unit for supplying power
to the first power supply unit when power is supplied to the
load in a closed state of the main switching unit.
Upon receiving the start-up signal from the
manipulation switch, the control unit outputs an initial

drive signal for putting the main switch element in a
conducting state to the main switching unit before a power
source for supplying power to the first power supply unit is
switched from the second power supply unit to the third
power supply unit.
With such configuration, when the load is started,
power is supplied to the load by putting the main switch
element of the main switching unit in a conducting state,
earlier than ensuring an inner power supply of the load
control device by putting the third power supply unit in a
conducting state. Accordingly, since a high current (inrush
current) generated in start-up of the load flows into the
main switch element of the main switching unit, instead of
making it flow in the third power supply unit, elements
forming the third power supply unit and the like are
protected from high current and prevented from being broken.
Further, since the main switching unit is designed and
manufactured to withstand a high voltage and high current,
it is possible to prevent any immediate breakage due to the
inrush current and a malfunction of the load control device.
In accordance with a second aspect of the present
invention, there is provided a two-wire load control device
connected in series between an AC power source and a load,
including: a main switching unit which includes a switch
element having a transistor structure, and controls a supply
of power to the load; an auxiliary switching unit which

includes a switch element having a thyristor structure, and
controls the supply of power to the load when the main
switching unit is in a non-conducting state; a control unit
which controls opening/closing of the main switching unit
and the auxiliary switching unit; a first power supply unit,
to which power is supplied from both terminals of the main
switching unit through a rectifying unit, for supplying a
stable voltage to the control unit; a second power supply
unit, to which power is supplied from both terminals of the
main switching unit through the rectifying unit, for
supplying power to the first power supply unit when no power
is supplied to the load; a third power supply unit for
supplying power to the first power supply unit when power is
supplied to the load in a closed state of the main switching
unit or the auxiliary switching unit; a voltage detection
unit which detects a voltage inputted to the third power
supply unit; and a zero-cross detection unit which detects a
zero-cross point of a load current.
Further, when power is supplied to the load, the
control unit causes a rise of a main switching unit drive
signal for putting the main switching unit in a conducting
state if the voltage detection unit detects that the voltage
inputted to the third power supply unit reaches a
predetermined threshold within a predetermined standby time
limit after the zero-cross detection unit detects the zero-
cross point of the load current, and starts supplying the

main switching unit drive signal after a predetermined
period, that is shorter than half cycle of the load current,
after the zero-cross detection unit detects the zero-cross
point of the load current.
Further, when power is supplied to the load, the
control unit causes a rise of the main switching unit drive
signal after the standby time limit is elapsed if the
voltage detection unit fails to detect that the voltage
inputted to the third power supply unit reaches a
predetermined threshold within the standby time limit, and
starts supplying the main switching unit drive signal after
a predetermined period, that is shorter than half cycle of
the load current, after the zero-cross detection unit
detects the zero-cross point of the load current.
With such configuration, when the voltage detection
unit detects that the voltage inputted to the third power
supply unit reaches a predetermined threshold, since the
control unit puts the main switching unit in a conducting
state (closed state), power is supplied from the main
switching unit to the load for most of the half cycle of the
alternating current power source. Further, since there is a
limitation on the standby time of the start of conduction of
the main switching unit, for example, if it is overly
delayed for the voltage inputted to the third power supply
unit in a low load to reach a predetermined threshold, the
main switching unit is put in a conducting state after the

standby time limit is elapsed. Accordingly, it is possible
to stably perform the switching operation in the main
switching unit every half cycle, and prevent the lighting
fluctuation from occurring in a low load such as miniature
bulb lighting. Further, since the main switch element
having a transistor structure used in the main switching
unit is in an active state in a low load, the main switch
element has a resistance. However, in the low load, since
the current flowing in the main switch element becomes small,
there is no excessive heating.
In accordance with a third aspect of the present
invention, there is provided a two-wire load control device
connected in series between an AC power source and a load,
including: a main switching unit which includes a switch
element having a transistor structure, and controls a supply
of power to the load; an auxiliary switching unit which
includes a switch element having a thyristor structure, and
controls the supply of power to the load when the main
switching unit is in a non-conducting state; a control unit
which controls opening/closing of the main switching unit
and the auxiliary switching unit; a first power supply unit,
to which power is supplied from both terminals of the main
switching unit through a rectifying unit, for supplying a
stable voltage to the control unit; a second power supply
unit, to which power is supplied from both terminals of the
main switching unit through the rectifying unit, for

supplying power to the first power supply unit when no power
is supplied to the load; a third power supply unit for
supplying power to the first power supply unit when power is
supplied to the load in a closed state of the main switching
unit or the auxiliary switching unit; a voltage detection
unit which detects a voltage inputted to the third power
supply unit; and a current detection unit which detects a
current flowing into the auxiliary switching unit.
Further, when power is supplied to the load, the
auxiliary switching unit is put in a conducting state if the
voltage detection unit detects that the voltage inputted to
the third power supply unit reaches a predetermined
threshold, and the control unit puts the main switching unit
in a conducting state and simultaneously puts the auxiliary
switching unit in a non-conducting state if the current
detection unit detects that the current flowing into the
auxiliary switching unit reaches a predetermined threshold.
With such configuration, if the voltage inputted to
the third power supply unit reaches a predetermined
threshold, the control unit first puts the auxiliary
switching unit in a conducting state (closed state). Then,
if the current flowing in the auxiliary switching unit
reaches a predetermined threshold, the control unit puts the
main switching unit in a conducting state. Accordingly,
power can be supplied from the main switching unit to the
load for most of the half cycle of the alternating current

power source. Meanwhile, in a low load, since the current
flowing in the auxiliary switching unit does not reach a
predetermined threshold, the main switching unit with large
power consumption is not put in a conducting state and the
electrical conduction is performed by the auxiliary
switching unit. Thus, in case of applying, e.g., an
illumination apparatus as the load, it is possible to reduce
the power consumed in the load control device when a
miniature bulb serving as a low load is turned on.
In accordance with a fourth aspect of the present
invention, there is provided a two-wire load control device
connected in series between an AC power source and a load,
including: a main switching unit which includes a switch
element having a transistor structure, and controls a supply
of power to the load; an auxiliary switching unit which
includes a switch element having a thyristor structure, and
controls the supply of power to the load when the main
switching unit is in a non-conducting state; a control unit
which controls opening/closing of the main switching unit
and the auxiliary switching unit; a first power supply unit,
to which power is supplied from both terminals of the main
switching unit through a rectifying unit, for supplying a
stable voltage to the control unit; a second power supply
unit, to which power is supplied from both terminals of the
main switching unit through the rectifying unit, for
supplying power to the first power supply unit when no power

is supplied to the load; a third power supply unit for
supplying power to the first power supply unit when power is
supplied to the load in a closed state of the main switching
unit or the auxiliary switching unit; a voltage detection
unit which detects a voltage inputted to the third power
supply unit; and a manipulation unit which is manipulated by
a user to adjust a current flowing in the load.
Further, the control unit sets a main switching unit
conducting time which is counted in order to put the main
switching unit in a conducting state every half cycle of the
AC power source in response to a manipulation inputted to
the manipulation unit, and the control unit puts the main
switching unit in a conducting state only while a
predetermined period, which is counted from when the voltage
detection unit detects that the voltage inputted to the
third power supply unit reaches a predetermined threshold,
overlaps with the main switching unit conducting time.
With such configuration, when the voltage detection
unit detects that the voltage inputted to the third power
supply unit reaches a predetermined threshold, since the
control unit puts the main switching unit in a conducting
state (closed state), power is supplied from the main
switching unit to the load for most of the half cycle of the
alternating current power source. Further, since the
conduction of the main switching unit is intermittently
controlled by the manipulation inputted to the manipulation

unit, it is possible to reduce the power consumption by
performing a desired operation on the load using the two-
wire load control device. For example, in a case where the
load is an illumination apparatus, the user may manipulate
the manipulation unit such that dimming is performed at a
desired brightness level. Further, since the switch element
of the main switching unit 11 has a transistor structure, it
is possible to achieve miniaturization of the load control
device generating less heat.
Brief Description of the Drawings
The objects and features of the present invention will
become apparent from the following description of
embodiments, given in conjunction with the accompanying
drawings, in which:
FIG. 1 is a circuit diagram showing a configuration of
a load control device in accordance with a first embodiment
of the present invention;
FIG. 2 is a time chart showing waveforms of currents
and control signals in respective parts in an operation of
the load control device in accordance with the first
embodiment;
FIG. 3 is a circuit diagram showing a configuration of
a load control device in accordance with a second embodiment
of the present invention;

FIG. 4 is a time chart showing waveforms of currents
and control signals in respective parts in an operation of
the load control device in accordance with the second
embodiment;
FIG. 5A is a circuit diagram of a main switch element
of the second embodiment having a lateral dual gate
transistor structure in which a withstand voltage
maintaining region is provided at one location;
FIG. 5B is a circuit diagram when two MOSFET type
transistors are connected in a reverse direction in a
comparison example;
FIG. 6 is a plan view of the main switch element
having a dual gate transistor structure;
FIG. 7 is a longitudinal cross-sectional view of the
main switch element having a dual gate transistor structure;
FIG. 8 is a circuit diagram showing a configuration
example of the drive circuit shown in FIG. 3;
FIG. 9 is a circuit diagram showing a specific
configuration example of the drive circuit;
FIG. 10 is a circuit diagram showing a modification
example of the drive circuit shown in FIG. 9;
FIG. 11 is a circuit diagram showing another
modification example of the drive circuit shown in FIG. 9;
FIG. 12 is a circuit diagram showing another specific
configuration example of the drive circuit shown in FIG. 3;
FIG. 13 is a circuit diagram showing a modification

example of the drive circuit shown in FIG. 12;
FIG. 14 is a circuit diagram showing another specific
configuration of the drive circuit shown in FIG. 3;
FIG. 15 is a circuit diagram showing a configuration
of a load control device in accordance with a third
embodiment of the present invention;
FIG. 16 is a plan view of a main switch element of the
third embodiment having a lateral single gate transistor
structure in which a withstand voltage maintaining region is
provided at one location;
FIG. 17 is a longitudinal cross-sectional view of the
main switch element having a single gate transistor
structure;
FIG. 18 is a circuit diagram showing a configuration
of a load control device in accordance with a fourth
embodiment of the present invention;
FIG. 19 is a circuit diagram showing a configuration
example of a main switching unit applied to the load control
device in accordance with the fourth embodiment;
FIG. 2 0 is a circuit diagram showing a configuration
example of a voltage detection unit applied to the load
control device in accordance with the fourth embodiment;
FIG. 21 is a time chart showing, in a high load,
waveforms of signals in respective parts of the load control
device in accordance with the fourth embodiment;
FIG. 22 is a time chart showing, in a low load,

waveforms of signals in respective parts of the load control
device in accordance with the fourth embodiment, in case of
controlling the main switching unit without setting a
standby time limit in a first pulse signal;
FIG. 23 is a time chart showing, in a low load,
waveforms of signals in respective parts of the load control
device in accordance with the fourth embodiment, in case of
controlling the main switching unit by setting a standby
time limit in a first pulse signal;
FIG. 24 is a circuit diagram showing a configuration
of a load control device in accordance with a fifth
embodiment of the present invention;
FIG. 25 is a circuit diagram showing a configuration
of a load control device in accordance with a sixth
embodiment of the present invention;
FIG. 2 6 is a time chart showing, in a high load,
waveforms of signals in respective parts of the load control
device in accordance with the sixth embodiment;
FIG. 27 is a time chart showing, in a low load,
waveforms of signals in respective parts of the load control
device in accordance with the sixth embodiment;
FIG. 28 illustrates a configuration example of the
current detection unit applied to the load control device in
accordance with the sixth embodiment;
FIG. 29 is a circuit diagram showing a configuration
of a load control device in accordance with a seventh

embodiment of the present invention;
FIG. 30 is a time chart showing, in a high load,
waveforms of signals in respective parts of the load control
device in accordance with the seventh embodiment;
FIG. 31 is a time chart showing, in a low load,
waveforms of signals in respective parts of the load control
device in accordance with the seventh embodiment;
FIG. 32 is a circuit diagram showing a configuration
of a load control device in accordance with an eighth
embodiment of the present invention;
FIG. 33 is a time chart showing, in a normal operation,
waveforms of signals in respective parts of the load control
device in accordance with the eighth embodiment;
FIG. 34 is a time chart showing, in a dimming
operation, waveforms of signals in respective parts of the
load control device in accordance with the eighth
embodiment;
FIG. 35 is a circuit diagram showing a configuration
of a load control device in accordance with a ninth
embodiment of the present invention;
FIG. 36 is a time chart showing, in a normal operation,
waveforms of signals in respective parts of the load control
device in accordance with the ninth embodiment;
FIG. 37 is a time chart showing, in a dimming
operation, waveforms of signals in respective parts of the
load control device in accordance with the ninth embodiment;

FIG. 38 illustrates a longitudinal cross-sectional
configuration of a main switch element having a lateral dual
gate transistor structure;
FIG. 39 is a circuit diagram showing a configuration
of a load control device in accordance with a tenth
embodiment of the present invention;
FIG. 40 is a circuit diagram showing a configuration
of a load control device in accordance with an eleventh
embodiment of the present invention;
FIG. 41 is a circuit diagram showing a configuration
of a load control device in accordance with a twelfth
embodiment of the present invention;
FIG. 42 is a circuit diagram showing a configuration
of a drive circuit applied to load control devices in
accordance with thirteenth to fifteenth embodiments of the
present invention;
FIG. 43 is a circuit diagram showing a configuration
of a load control device of a first conventional example;
and
FIG. 44 is a circuit diagram showing a configuration
of a load control device of a second conventional example.
Detailed Description of the Embodiments
Hereinafter, embodiments of the present invention will
be described with reference to the accompanying drawings

which form a part hereof. Throughout the specification and
drawings, like reference numerals will be given to like
parts having substantially the same function and
configuration, and redundant description thereof will be
omitted.
(First Embodiment)
A load control device in accordance with a first
embodiment of the present invention will be described with
reference to FIGS. 1 and 2. FIG. 1 is a circuit diagram
showing a configuration of a load control device 1A in
accordance with the first embodiment of the present
invention. FIG. 2 is a time chart showing waveforms of
currents and control signals in respective parts thereof. A
case where a triac is used as a main switch element of a
main switching unit as in a conventional case will be
described in the first embodiment. Further, a load 3 may be
an apparatus using a motor such as a ventilator or an
illumination apparatus, but it is not limited thereto.
As shown in FIG. 1, the load control device 1A
connected in series between a commercial AC power source 2
and a load 3 includes a main switching unit 11 to control
the supply of power to the load 3, a rectifying unit 12, and
a control unit 13 controlling the entire load control device
1A. The load control device 1A further includes a first
power supply unit 14 which supplies a stable power to the
control unit 13, a second power supply unit 15 which

supplies power to the first power supply unit 14 when no
power is supplied to the load 3, and a third power supply
unit 16 which supplies power to the first power supply unit
14 when power is supplied to the load 3. Also, the load
control device 1A includes an auxiliary switching unit 17
which supplies to a gate of the main switch element a
sufficient amount of a current to put a main switch element
11a of the main switching unit 11 in a conducting state, and
the like.
The main switching unit 11 includes a triac configured
as the main switch element 11a (hereinafter, referred to as
"triac 11a" if necessary). Further, the control unit 13 is
configured to directly output a drive signal (pulse signal)
to the main switch element 11a of the main switching unit 11
without passing through the third power supply unit 16.
More specifically, when a manipulation switch (SW) 4 for
starting the load 3 is turned on, the control unit 13
outputs a drive signal to be directly inputted to the gate
of the triac 11a. Accordingly, since an inrush current
generated immediately after start-up of the load 3 flows
into the triac 11a of the main switching unit 11, elements
such as the third power supply unit 16 and the auxiliary
switching unit 17 are protected from high current.
Next, an operation of the load control device 1A in
accordance with the first embodiment of the present
invention will be described with reference to FIG. 2. In an

OFF state of the load control device 1A in which no power is
supplied to the load 3, a voltage applied from the
commercial AC power source 2 to the load control device 1A
is supplied to the second power supply unit 15 via the
rectifying unit 12. In an OFF state of the load 3, a ripple
current that is full-wave rectified by the rectifying unit
12 is inputted to the second power supply unit 15. Only
when a voltage applied thereto is higher than a Zener
voltage of a Zener diode 15a, the Zener voltage is inputted
to the first power supply unit 14. If the voltage that is
full-wave rectified by the rectifying unit 12 is lower than
the Zener voltage, a buffer capacitor 14a connected between
input terminals of the first power supply unit 14 serves as
a power source to supply power to the first power supply
unit 14. The buffer capacitor 14a repeats charging and
discharging. Further, in this case, the current flowing
into the load 3 is a micro-current small enough not to cause
a malfunction of the load 3. It is set such that the
consumption current of the control unit 13 is small and the
impedance of the second power supply unit 15 is set to be
maintained high. Further, the above description is not
illustrated in FIG. 2 since it is substantially the same as
the conventional case.
Meanwhile, when the manipulation switch (SW) 4 is
turned on to start to drive the load 3 and a start-up signal
is outputted from the manipulation switch 4, the control

unit 13 directly outputs an initial drive signal having one
pulse to the main switching unit 11. Accordingly, the triac
11a of the main switching unit 11 is put in a conducting
state and power is supplied to the load 3. As well known,
although an inrush current generated when the power is
inputted to the load 3 such as illumination apparatus and
motor is much larger than a load current flowing into the
load 3 in a normal state, the main switching unit 11 is
designed and manufactured to withstand the high current.
Accordingly, even though the inrush current flows in the
triac 11a or the like, an element such as triac 11a is
prevented from being broken.
Further, when a start-up signal is outputted from the
manipulation switch 4, the control unit 13 outputs a first
main switching unit drive signal, and simultaneously outputs
a drive enable signal for putting a switch element 16c of
the third power supply unit 16 in a conducting state. The
drive enable signal is continuously outputted until the
manipulation switch 4 is turned off.
The triac 11a is a self-hold element, which maintains,
once a pulse signal is inputted to the gate, a conducting
state until the input voltage becomes 0 V (zero-cross point).
Since the triac 11a is in a conducting state, the rectified
voltage of the rectifying unit 12 becomes almost zero.
Meanwhile, the second power supply unit 15 and the third
power supply unit 16 are put in a non-conducting state, and

there flows no current therein. Accordingly, power is
supplied to the first power supply unit 14 from the buffer
capacitor 14a and the terminal voltage of the buffer
capacitor 14a is reduced gradually.
When the voltage of the commercial AC power source
becomes 0 V, the triac 11a is subjected to the self-arc-
extinction and the rectified voltage of the rectifying unit
12 increases. Further, when the input voltage of the first
power supply unit 14, i.e., the terminal voltage of the
buffer capacitor 14a, becomes lower than the output voltage
of the third power supply unit 16, the third power supply
unit 16 starts the supply of power to the first power supply
unit 14, and at the same time, starts charging the buffer
capacitor 14a. When charging of the buffer capacitor 14a is
completed and the terminal voltage thereof becomes
substantially equal to the output voltage of the third power
supply unit 16, the current flowing in the third power
supply unit 16 is commutated to a Zener diode 16a, a
thyristor 17a of the auxiliary switching unit 17, and the
triac 11a of the main switching unit 11, and the triac 11a
is put in a conducting state. Accordingly, power of a
normal state is supplied to the load 3 from the main
switching unit 11. Then, a self power reserve for the
circuit of the load control device 1A, a conducting
operation of the auxiliary switching unit 17 and a
conducting operation of the main switching unit 11 are

repeated every half cycle of AC current.
Further, as shown in FIG. 2, a timing of outputting
the initial drive signal may not coincide with the zero-
cross point of the commercial AC power source. In order to
make them coincide, a zero-cross detection circuit may be
provided such that the initial driving signal is outputted
when the zero-cross detection circuit detects a zero-cross
point. The same can be applied to the following embodiments.
(Second Embodiment)
Next, a load control device in accordance with a
second embodiment of the present invention will be described
with reference to FIGS. 3 to 7. A main switch element used
in a load control device IB in accordance with the second
embodiment of the present invention is different from the
conventional triac in that it has a lateral dual gate
transistor structure having one withstand voltage
maintaining region is provided at one location. FIG. 3 is a
circuit diagram showing a configuration of the load control
device IB in accordance with the second embodiment of the
present invention. FIG. 4 is a time chart showing waveforms
of currents and control signals in respective parts thereof.
FIG. 5A is a circuit diagram of a main switch element having
a lateral dual gate transistor structure in which a
withstand voltage maintaining region is provided at one
location, which is used as a main switch element lib of a
main switching unit 11 in the second embodiment. FIG. 5B is

a circuit diagram when two MOSFET type transistors are
connected in a reverse direction in a comparison example.
FIG. 6 is a plan view of a main switch element having a
lateral dual gate transistor structure. FIG. 7 is a
longitudinal cross-sectional view taken along line VH-VH of
FIG. 6.
In the configuration of FIG. 5B, source electrodes S
of two transistors are connected to each other and also
grounded (the lowest potential portion). A withstand
voltage is not required between the source electrode S and
the gate electrodes Gl and G2, and a withstand voltage is
required to be maintained between the gate electrodes Gl and
G2 and the drain electrodes Dl and D2. Accordingly, the
withstand voltage maintaining region (e.g., having a width
of a withstand voltage maintaining distance) needs to be
provided at two locations. Since the two transistors are
operated by a gate signal provided using the source
electrode as a reference, they can be driven by inputting
the same drive signal to the gate electrodes Gl and G2 of
the respective transistors.
In contrast, as shown in FIGS. 6 and 7, a main switch
element having a lateral dual gate transistor structure is a
bidirectional element that can reduce its loss by providing
a withstand voltage maintaining region at one location.
That is, each of the drain electrodes Dl and D2 is formed on
a GaN layer, and each of the gate electrodes Gl and G2 is

formed on an AlGaN layer. In a state where a voltage is not
applied to the gate electrodes Gl and G2, there occurs a
void of electrons in a two-dimensional electron gas layer
generated at a hetero interface between AlGaN and GaN below
the gate electrodes Gl and G2 and there flows no current
therein. Meanwhile, when a voltage is applied to the gate
electrodes Gl and G2, a current flows at the hetero
interface between AlGaN and GaN from the drain electrode Dl
to the drain electrode D2 (or vice versa) . A withstand
voltage is required to be maintained between the gate
electrodes Gl and G2, so that it is required to provide a
predetermined distance. However, a withstand voltage is not
required between the drain electrode Dl and the gate
electrode Gl and between the drain electrode D2 and the gate
electrode G2. Accordingly, the drain and gate electrodes Dl
and Gl may overlap with each other and the drain and gate
electrodes D2 and G2 may overlap with each other through an
insulating layer In. Further, the element having such
configuration needs to be controlled by using the voltages
of the drain electrodes Dl and D2 as references, and it is
necessary to input a drive signal into each of gate
electrodes Gl and G2 (thus, it is referred to as a dual gate
transistor structure).
The load control device IB shown in FIG. 3 includes
the main switch element lib of the main switching unit 11
having a dual gate transistor structure (schematically shown

in the drawing). Accordingly, only while a control signal
is inputted to each of the gate electrodes Gl and G2, the
main switch element lib of the main switching unit 11 is in
a conducting state. Accordingly, it is necessary to
generate a first pulse signal for driving the main switch
element lib. In the configuration example shown in FIG. 3,
a third power supply unit 16 includes a voltage detection
unit 18 which detects a voltage inputted to the third power
supply unit 16. Also, a control unit 13 includes a first
pulse output unit (main switching unit drive signal output
unit) 21 which outputs a first pulse signal in response to a
detection signal from the voltage detection unit 18, and a
second pulse output unit 22 which outputs a second pulse
signal for putting a thyristor 17a of an auxiliary switching
unit 17 in a conducting state for a predetermined period
after the main switching unit 11 is put in a non-conducting
state. Further, differently from the first embodiment, the
auxiliary switching unit 17 carries out the supply of power
to the load 3 when the load current is low.
Next, an operation of the load control device IB in
accordance with the second embodiment of the present
invention will be described with reference to FIG. 4. When
the manipulation switch (SW) 4 is turned on to start to
drive the load 3 and a start-up signal is outputted from the
manipulation switch 4, an initial drive signal having a
predetermined pulse width is outputted from a main control

part 20 of the control unit 13 to the main switching unit 11
directly or through the first pulse output unit 21.
Accordingly, the main switch element lib of the main
switching unit 11 is put in a conducting state and power is
supplied to the load 3. As well known, although an inrush
current generated when power is inputted to the load 3 such
as illumination apparatus and motor is much larger than a
load current flowing into the load 3 in a normal state, the
main switch element lib is designed and manufactured to
withstand the high current. Accordingly, even though the
inrush current flows in the main switch element lib, an
element such as the main switch element lib is prevented
from being broken. Further, since the drive enable signal
is substantially the same as that of the first embodiment,
and a description thereof will be omitted.
The main switch element lib of the second embodiment
is put in a conducting state only while a specific voltage
is applied to the gate electrodes Gl and G2 in a different
way from the triac. Accordingly, the pulse width of the
initial drive signal is larger than 1/4 cycle and smaller
than 1/2 cycle of the commercial AC power source, and is set
to be longer than the first pulse signal. If the initial
drive signal is absent (drops), the main switching unit 11
is put in a non-conducting state (open state). Accordingly,
the second pulse output unit 22 outputs a second pulse
signal to put the auxiliary switching unit 17 in a

conducting state (closed state) only for a second
predetermined period (e.g., several hundred u seconds).
Consequently, the main switching unit 11 is put in a non-
conducting state and the load current is commutated to the
auxiliary switching unit 17, and power is supplied to the
load 3 from the thyristor 17a of the auxiliary switching
unit 17. Since the thyristor 17a is a self-arc-extinction
type switch element, the thyristor 17a is automatically put
in a non-conducting state when a voltage value of the load
current becomes 0 V (zero-cross point).
If both the main switching unit 11 and the auxiliary
switching unit 17 are put in a non-conducting state, the
rectified voltage of a rectifying unit 12 begins to increase,
and the current flows in the third power supply unit 16 to
start charging a buffer capacitor 14a. As described above,
the voltage detection unit (charging monitoring unit) 18 is
provided in the third power supply unit 16 to detect an
input voltage of the third power supply unit 16 or a
terminal voltage of the buffer capacitor 14a (i.e., full
charging of the buffer capacitor 14a) . If the voltage
detection unit 18 detects that the input voltage of the
third power supply unit 16 or the terminal voltage of the
buffer capacitor 14a reaches a predetermined threshold, the
voltage detection unit 18 outputs a specific detection
signal. When the first pulse output unit 21 of the control
unit 13 receives the detection signal from the voltage

detection unit 18, in order to put the main switching unit
11 in a conducting state (closed state) for a first
predetermined period, the first pulse output unit 21 outputs
a first pulse signal (main switching unit drive signal) to a
drive circuit 10 for putting the main switching unit 11 in a
conducting state.
Further, in FIG. 3, the first pulse output unit (main
switching unit drive signal output unit) 21 is configured by
hardware with a dedicated IC and the like and is provided as
a part of the control unit 13 to directly output the first
pulse signal in response to the detection signal from the
voltage detection unit 18. However, it is not limited
thereto. For example, it may be configured such that the
output of the voltage detection unit 18 is inputted to the
main control part 20 including a CPU and the like and the
first pulse signal is outputted by software.
If the first pulse signal is absent (drops), the main
switching unit 11 is put in a non-conducting state (open
state). Accordingly, the second pulse output unit 22
outputs a second pulse signal to put the auxiliary switching
unit 17 in a conducting state (closed state) only for a
second predetermined period (e.g., several hundred u
seconds). The thyristor 17a of the auxiliary switching unit
17 is put in a conducting state such that power is supplied
to the load 3 until the thyristor 17a is subjected to the
self-arc-extinction. Then, a self power reserve for the

circuit of the load control device IB, a conducting
operation of the auxiliary switching unit 17 and a
conducting operation of the main switching unit 11 are
repeated every half cycle of alternating current.
Since these operations are performed with respect to
the load current, although the main switching unit 11
includes the main switch element lib having a transistor
structure, it is possible to achieve a two-wire load control
device which is applicable to any one of a fluorescent lamp,
incandescent lamp and the like without being limited to
those having a power factor of 1. Further, since the main
switching unit 11 includes the main switch element lib
having a lateral dual gate transistor structure, a withstand
voltage maintaining region in the transistor is limited to
one location. Accordingly, it is possible to reduce the
amount of heat generated by the main switch element when
power is supplied to the load, thereby achieving both
miniaturization and high capacity of the load control device.
Further, although FIG. 3 illustrates the example of
providing a current detection unit 2 6 for detecting the
current flowing into the auxiliary switching unit 17, this
is to protect the auxiliary switching unit 17 from being
broken by performing an operation of switching a load
current path from the auxiliary switching unit 17 to the
main switching unit 11 when the frequency is deviated or
overload is connected. Accordingly, the current detection

unit 26 is not positively necessary and may be provided if
necessary.
FIG. 8 is a circuit diagram showing a configuration
example of the drive circuit 10. The drive circuit 10 for
driving the main switching unit 11 includes diodes 101a and
101b having two diodes corresponding to the dual gates of
the main switch element lib and connected to a first power
supply unit 14 of the load control device IB, capacitors
102a and 102b having one ends connected to respective power
lines and the other ends connected to the diodes 101a and
101b, and drive switch elements 103a and 103b connected
between gate terminals of the main switch element lib of the
main switching unit 11 and connection points between the
diodes 101a and 101b and the capacitors 102a and 102b. The
drive switch elements 103a and 103b are turned on/off based
on a signal transmitted from the control unit 13. Further,
each of the drive switch elements 103a and 103b has a
configuration in which a switch portion is isolated from a
control portion. The configuration of each of the drive
switch elements 103a and 103b is not particularly limited
thereto. As will be described later, various types of
elements, e.g., an optically coupled semiconductor switch
element such as photocoupler and photorelay may be used.
With such configuration, the first power supply unit
14 of the load control device IB is connected to the other
ends of the capacitors 102a and 102b having respective one

ends connected to the power lines via the diodes 101a and
101b. Accordingly, a simple power source using the
potential of the power lines as a reference is configured by
the capacitors 102a and 102b. The capacitor connected to
the side having a low voltage is charged by the current
flowing into the power line having a low voltage from the
power line having a high voltage via an inner power supply
of the load control device IB to thereby charge the
capacitors 102a and 102b. In this case, since the capacitor
connected to the side having a high voltage is not charged,
charging of the capacitor is repeated every one cycle of the
power frequency. The capacitor on the opposite side is
charged at a timing reverse to that in the above
relationship between the potentials of power lines.
In a case where the main switch element lib having a
lateral dual gate transistor structure is switched from an
OFF state to an ON state, a voltage provided using
connection point connected to the power line (see FIG. 5A)
needs to be applied to the gate of the main switch element
lib. In this case, when the drive switch element 103a or
103b connected to the gate electrode of the main switch
element lib of the main switching unit 11 is put in a
conducting state based on a signal transmitted from the
control unit 13, since a voltage, which is charged in each
of the capacitors by using the power line as a reference is
applied to the gate terminal of the main switch element lib,

the main switch element lib is put in a conducting state
(closed state). Once the main switch element lib is put in
a conducting state, since a voltage between terminals of the
main switch element lib becomes very small, the conducting
state can be maintained by a voltage applied from the power
source of the load control device IB via the diodes 101a and
101b and the drive switch elements 103a and 103b.
Since the drive circuit 10 is non-isolated from the
first power supply unit 14 in this embodiment, it is
possible to supply a driving power with high efficiency.
The capacitors 102a and 102b may have a small size or a
small capacity since it is preferable to temporarily fix the
potential of the gate electrode when the main switch element
lib is switched from an OFF state to an ON state. Further,
power is supplied to the drive circuit 10 from a power
supply unit having a relatively stable input or output, such
as the first power supply unit 14.
FIG. 9 illustrates a specific configuration example of
the drive circuit 10, wherein an optically coupled
semiconductor switch element such as a photocoupler and a
photorelay is used as the drive switch elements 103a and
103b. When a drive signal is inputted from the control unit
13, an optical signal is outputted from a light emitting
part of the optically coupled semiconductor switch element.
When the optical signal is inputted to a light receiving
part, the light receiving part is put in a conducting state

and the current (drive signal) from the first power supply
unit 14 flows therein. Since the light emitting part is
electrically isolated from the light receiving part, a drive
signal is not inputted to the gate electrode of the main
switch element lib unless light is outputted from the light
emitting part. Accordingly, it is possible to easily and
surely turn on/off each of the drive switch elements 103a
and 103b connected to the gate electrodes of the main switch
element lib while maintaining electrical isolation on the
basis of the drive signal transmitted from the control unit
13.
FIG. 10 illustrates a modification example of the
drive circuit 10 shown in FIG. 9. In this modification
example, the light emitting parts of the drive switch
elements 103a and 103b using the optically coupled
semiconductor switch elements such as photocouplers and
photorelays are connected in series. Accordingly, the
current flowing into the drive circuit 10 can be reduced by
about 1/2, thereby reducing the power consumption in the
drive circuit 10.
FIG. 11 illustrates another modification example of
the drive circuit 10 shown in FIG. 9. In this modification
example, the light emitting parts of the drive switch
elements 103a and 103b using the optically coupled
semiconductor switch elements such as photocouplers and
photorelays are connected in series. Further, capacitors

104a and 104b are connected between the power lines each of
which is used as a reference of the gate electrode and
connection points between the gate electrodes of the main
switch element lib of the main switching unit 11 and the
drive switch elements 103a and 103b. Further, the
capacitors 104a and 104b may be added to the configuration
example of the drive circuit 10 shown in FIG. 9.
By adding the capacitors 104a and 104b as shown in the
modification example, when the drive switch elements 103a
and 103b are turned on/off, the capacitors 104a and 104b
make it possible to mitigate a sudden change in voltage
applied to the gate electrodes of the main switch element
lib and to prevent the main switch element lib from being
rapidly turned on and off. Consequently, it is possible to
reduce the noise generated when the main switch element lib
of the main switching unit 11 is turned on/off, thereby
reducing the size of the noise filter or omitting the noise
filter. That is, compared to the conventional configuration
illustrated in FIG. 43, a coil or capacitor serving as the
noise filter may be omitted.
With regard to the coil serving as the noise filter,
the coil becomes large-sized as the rated current of the
load control device increases. Accordingly, if the coil can
be omitted, it is possible to achieve miniaturization of the
load control device. With regard to the capacitor serving
as the noise filter, it has less restriction on the size of

the load control device compared to the coil. However, the
presence of the capacitor leads to a reduction in impedance
of the load control device in an OFF state of the load
control device, and it is undesirable for an OFF state of
the load control device. Further, an alternating current
flows through the capacitor even in an OFF state of the load
control device. Accordingly, a malfunction of the load may
occur in an OFF state. Thus, in the two-wire load control
device, it is preferable to omit the capacitor serving as
the noise filter from the load control device.
FIG. 12 is a circuit diagram showing another specific
configuration example of the drive circuit 10. The drive
circuit 10 includes two optically coupled semiconductor
switch elements 201 and 202 such as photocouplers
corresponding to the dual gates of the main switch element
lib, and the like. A drive signal is inputted from the
control unit 13 to each of light emitting parts 201a and
2 02a of the optically coupled semiconductor switch elements
201 and 202. Upon receiving the drive signal, each of the
light emitting parts 201a and 202a of the optically coupled
semiconductor switch elements 201 and 2 02 converts the power
into optical energy and outputs the optical energy. When
light from the light emitting parts 201a and 202a is
incident on light receiving parts 201b and 202b of the
optically coupled semiconductor switch elements 201 and 202,
photoelectric conversion is performed in each of the light

receiving parts 201b and 202b, to convert the optical energy
into electric energy (i.e., generate power). Each of the
light receiving parts 201b and 202b is connected such that
the power is generated therefrom to apply a positive
potential to the gate of the main switch element lib of the
main switching unit 11 by using as a reference each of the
connection points respectively connected to the AC power
source (commercial AC power source) and the load (see FIG.
5A) .
The light emitting parts 201a and 202a of the
optically coupled semiconductor switch elements 201 and 202
emit light based on the drive signal outputted from the
control unit 13. Accordingly, it is possible to easily
input the drive signal to the gate electrodes of the main
switch element lib of the main switching unit 11 having a
different reference potential, and put the main switch
element lib of the main switching unit 11 in a conducting
state (closed state) . Further, since each of the light
emitting parts 201a and 202a of the optically coupled
semiconductor switch elements 201 and 202 is electrically
isolated from each of the light receiving parts 201b and
202b thereof, a drive signal is not inputted to the gate
electrode of the main switch element lib unless light is
outputted from the light emitting parts 201a and 202a. That
is, the gate electrode of the main switch element lib is
supplied with a power that is electrically isolated from the

control unit 13 (or the first power supply unit 14 of the
load control device IB) and is different from the drive
signal outputted from the control unit 13. Further, it is
possible to easily and surely turn on/off each of the
optically coupled semiconductor switch elements 201 and 202
connected to the gate electrode of the main switch element
lib while maintaining electrical isolation on the basis of
the drive signal transmitted from the control unit 13.
FIG. 13 illustrates a modification example of the
drive circuit 10 shown in FIG. 12. In this modification
example, the light emitting parts 201a and 202a of the
optically coupled semiconductor switch elements 201 and 202
such as photocouplers are connected in series. Accordingly,
the current flowing into the drive circuit 10 can be reduced
by about 1/2, thereby reducing the power consumption of the
drive circuit 10.
FIG. 14 is a circuit diagram showing another specific
configuration of the drive circuit 10. In this
configuration example, the drive circuit 10 includes a
transformer (electromagnetic coupling element) 203 such as a
high-frequency isolation transformer to transmit power by
electromagnetic coupling, rectifier circuits 204a and 204b,
an oscillation circuit 205 and the like. A primary coil
203a of the transformer 203 is connected to the oscillation
circuit 205, and the oscillation circuit 205 is connected to
the control unit 13. When a drive signal transmitted from

the control unit 13 is inputted to the oscillation circuit
205, the oscillation circuit 205 performs oscillation to
generate an alternating current power only while the drive
signal is applied. When the alternating current generated
by the oscillation circuit 205 flows in the primary coil
203a of the transformer 203, an electromotive force is
generated in secondary coils 203b and 203c by
electromagnetic induction. Since the electromotive force
generated in the secondary coils 203b and 203c of the
transformer 203 is an alternating current, it is rectified
by the rectifier circuits 204a and 204b to be inputted to
the gate electrodes of the main switch element lib of the
main switching unit 11. Further, the rectifier circuits
204a and 204b are connected to apply a positive potential to
the gate electrodes of the main switch element lib by using
as a reference the connection points respectively connected
to the commercial AC power source and the load. Further,
since the primary coil 203a and the secondary coils 203b and
203c of the transformer 203 are electrically isolated from
each other, a drive signal is not inputted to the gate
electrodes of the main switch element lib unless the current
flows in the primary coil 203a of the transformer 203. That
is, the gate electrodes of the main switch element lib are
supplied with a power that is electrically isolated from the
control unit 13 and is different from the drive signal
outputted from the control unit 13.

As described above, since an alternating current power
is generated by the oscillation circuit 205 by using the
drive signal outputted from the control unit 13 as a trigger,
it is possible to generate a desired power in the secondary
coils 203b and 203c of the transformer 203 by appropriately
setting the oscillation frequency and amplitude of the
oscillation circuit 205, the numbers of turns of the primary
coil 203a and the secondary coils 203b and 203c of the
transformer 203, and the like. Accordingly, even in a
current type main switch element in which the gate of the
main switch element lib of the main switching unit 11
requires a current value equal to or greater than a
predetermined value, it can be stably driven. Further, the
driving power of the oscillation circuit 205 is supplied
from any power supply unit of the load control device.
Although not shown in the drawing, the oscillation circuit
2 05 may be omitted such that the control unit 13 directly
outputs a pulse signal having a predetermined frequency and
predetermined amplitude.
(Third Embodiment)
Next, a load control device in accordance with a third
embodiment of the present invention will be described with
reference to FIGS. 15 to 17. A main switch element used in
a load control device 1C in accordance with the third
embodiment has a lateral single gate transistor structure in
which a withstand voltage maintaining region is provided at

two locations, which is different from the conventional
triac or the dual gate transistor structure. FIG. 15 is a
circuit diagram showing a configuration of the load control
device 1C in accordance with the third embodiment of the
present invention. FIG. 16 is a plan view of the main
switch element having a lateral single gate transistor
structure. FIG. 17 is a longitudinal cross-sectional view
taken along line XVU-XVII of FIG. 16.
Compared to the second embodiment using the main
switch element lib having a dual gate transistor structure
shown in FIG. 3, in the third embodiment using a main switch
element lie having a single gate transistor structure shown
in FIG. 15, a first drive signal or a first pulse signal
outputted from the main control part 20 or the first pulse
output unit 21 is directly inputted to each of two elements
having a single gate transistor structure. Accordingly, the
drive circuit 10 is unnecessary. The other configuration of
the load control device 1C is the substantially same as that
of the load control device IB of FIG. 3 in accordance with
the second embodiment.
As shown in FIG. 17, a substrate 120 of the main
switch element lie includes a conductive layer 120a and a
GaN layer 120b and an AlGaN layer 120c stacked on the
conductive layer 120a. The main switch element lie uses, as
a channel layer, a two-dimensional electron gas layer
generated at a hetero interface between AlGaN and GaN. As

shown in FIG. 16, formed on a surface 120d of the substrate
120 are a first drain electrode Dl and a second drain
electrode D2 respectively connected in series to the
commercial AC power source 2 and the load 3, and a midpoint
potential portion S having a midpoint potential with respect
to the potentials of the first drain electrode Dl and the
second drain electrode D2. Further, a control electrode
(gate) G is formed on the midpoint potential portion S. For
example, a Schottky electrode is used as the control
electrode G.
The first drain electrode Dl has a comb shape
including a plurality of electrodes 111, 112, 113
arranged in parallel to each other, and the second drain
electrode D2 has a comb shape including a plurality of
electrodes 121, 122, 123 ... arranged in parallel to each
other. The electrodes 111, 112, 113 ... arranged in a comb
shape are disposed to face the electrodes 121, 122, 123 ...
arranged in a comb shape. The midpoint potential portion S
and the control electrode G are respectively arranged
between the electrodes 111, 112, 113 ... and 121, 122, 123 ...
arranged in a comb shape. The midpoint potential portion S
and the control electrode G are similar in a planar shape of
a space formed between the electrodes (approximately fish
spine shape).
Next, a lateral transistor structure of the switch
element lie will be described. As shown in FIG. 16, the

electrode 111 of the first drain electrode Dl and the
electrode 121 of the second drain electrode D2 are arranged
such that their central lines in the width direction are
located on the same line. A corresponding portion of the
midpoint potential portion S and a corresponding portion of
the control electrode G are provided in parallel to the
electrode 111 of the first drain electrode Dl and the
electrode 121 of the second drain electrode D2 respectively.
In the width direction, the distances between the electrode
111 of the first drain electrode Dl, the electrode 121 of
the second drain electrode D2, the corresponding portion of
the midpoint potential portion S and the corresponding
portion of the control electrode G are set as distances
capable of maintaining a predetermined withstand voltage.
The same is applied to a direction perpendicular to the
width direction, i.e., a length direction of the electrode
111 of the first drain electrode Dl and the electrode 121 of
the second drain electrode D2. Further, such relationship
is also applied to the other electrodes 112 and 122, 113 and
123. That is, the midpoint potential portion S and the
control electrode G are arranged at positions capable of
maintaining a predetermined withstand voltage with respect
to the first drain electrode Dl and the second drain
electrode D2.
As described above, the midpoint potential portion S
having a midpoint potential with respect to the potential of

the first drain electrode Dl and the potential of the second
drain electrode D2 and the control electrode G connected to
the midpoint potential portion S to control the midpoint
potential portion S are arranged at positions capable of
maintaining a predetermined withstand voltage with respect
to the first drain electrode Dl and the second drain
electrode D2. Accordingly, for example, in a case where the
first drain electrode Dl is on the high potential side and
the second drain electrode D2 is on the low potential side,
when the main switch element lie is turned off, i.e., when a
signal of 0 V is applied to the control electrode G, the
current is surely interrupted between at least the first
drain electrode Dl, the control electrode G and the midpoint
potential portion S (the current is inhibited immediately
below the control electrode (gate) G). Meanwhile, when the
main switch element lie is turned on, i.e., when a signal
having a voltage equal to or greater than a predetermined
threshold is applied to the control electrode G, as
represented by arrows in FIG. 16, the current flows in a
path of the first drain electrode Dl (electrodes 111, 112,
113 ... ) , the midpoint potential portion S, and the second
drain electrode D2 (electrodes 121, 122, 123 ... ) . The same
can be applied to the reverse case.
As described above, by forming the midpoint potential
portion S at a position capable of maintaining a
predetermined withstand voltage with respect to the first

drain electrode Dl and the second drain electrode D2,
although a threshold voltage of a signal applied to the
control electrode G is reduced to the lowest level, the
switch element lie can be surely turned on/off, and it is
possible to achieve a low temperature resistance. Further,
by configuring the main switching unit 11 using the switch
element lie, the ground (GND) of the control signal is set
to have the same potential as the midpoint potential portion
S. Accordingly, the commercial AC power source having a
high voltage can be directly controlled by the control unit
13 which is driven by a control signal of several voltages.
Further, since it is not affected by the voltage drop due to
the diode of the rectifying unit 12, although a threshold
voltage for converting the conducting state (closed
state)/non-conducting state (open state) of the main
switching unit 11 is low, it is possible to surely maintain
the non-conducting state (open state). Further, in the
lateral transistor element using, as a channel layer, a two-
dimensional electron gas layer generated at a hetero, there
is a trade-off relationship between the high potential of
the threshold voltage for putting the element in a non-
conducting state and the on resistance in a conducting state.
Accordingly, the on resistance can be maintained at a low
level by reducing the threshold voltage, thereby achieving
the small size and high capacity of the load control device
1C.

(Fourth Embodiment)
A load control device in accordance with a fourth
embodiment of the present invention will be described. FIG.
18 is a circuit diagram showing a configuration of a load
control device ID in accordance with the fourth embodiment
of the present invention. FIG. 19 is a circuit diagram
showing a configuration example of the main switching unit
11 applied to the load control device ID. FIG. 20 is a
circuit diagram showing a configuration example of the
voltage detection unit 18 applied to the load control device
ID. FIGS. 21 and 23 are time charts showing waveforms of
signals in respective parts of the load control device ID.
The load control device ID of the fourth embodiment
shown in FIG. 18 connected in series between the AC power
source 2 and the load 3 includes a main switching unit 11 to
control the supply of power to a drive circuit 10 and the
load 3, a rectifying unit 12, and a control unit 13
controlling the entire load control device ID. The load
control device ID further includes a first power supply unit
14 which supplies a stable power to the control unit 13, a
second power supply unit 15 which supplies power to the
first power supply unit 14 when no power is supplied to the
load 3, and a third power supply unit 16 which supplies
power to the first power supply unit 14 when power is
supplied to the load 3. Also, the load control device ID
includes an auxiliary switching unit 17 which allows a

micro-current in the load current to flow therethrough, and
the like. The drive circuit 10 drives the main switching
unit 11 in response to a pulse signal outputted from the
control unit 13. Further, the third power supply unit 16
includes a voltage detection unit 18 which detects a voltage
inputted to the third power supply unit 16, and a zero-cross
detection unit 19 which detects a zero-cross point of the
load current. The main switching unit 11 has a main switch
element lid (see FIG. 19) having a single gate transistor
structure, and the auxiliary switching unit 17 has an
auxiliary switch element 17a having a thyristor structure.
Further, the control unit 13 includes a main control part 20
including a CPU and the like, a first pulse output unit 21,
a second pulse output unit 22 and a third pulse output unit
23.
After receiving a charging completion signal of a
buffer capacitor 14a from the voltage detection unit 18, the
first pulse output unit 21 outputs a first pulse to put the
main switching unit 11 in a conducting state only for a
first predetermined period. That is, the first pulse rises
when receiving the charging completion signal from the
voltage detection unit 18, and drops after the first
predetermined period. Further, in a low load, the first
pulse output unit 21 makes the first pulse drop when
receiving a second pulse inputted from the second pulse
output unit 22 even before the first predetermined period

has elapsed.
The second pulse output unit 22 outputs the second
pulse such that the close state of the main switching unit
11 is limited to last for a second predetermined period
after the zero-cross detection unit 19 has detected a zero-
cross point of the power supply current. That is, the
second pulse rises when receiving a zero-cross detection
signal from the zero-cross detection unit 19, and drops
after the second predetermined period. The third pulse
output unit 23 outputs a third pulse signal from a
predetermined period to put the auxiliary switching unit 17
in a conducting state only for a third predetermined period
after detecting a non-conducting state (open state) of the
main switching unit 11. That is, the third pulse rises
after detecting the non-conducting state (open state) of the
main switching unit 11, and drops after the third
predetermined period.
Even in an OFF state of the load control device ID in
which no power is supplied to the load 3, a current flows in
the second power supply unit 15 from the power source 2
through the rectifying unit 12. Accordingly, although a
micro-current flows in the load 3, the current is suppressed
to a low level to avoid a malfunction in the load 3.
Accordingly, the impedance of the second power supply unit
15 is maintained at a high level.
When power is supplied to the load 3, the impedance of

the third power supply unit 16 is reduced such that a
current is made to flow in the inner circuit of the load
control device ID and the buffer capacitor 14a is charged.
As described above, the voltage detection unit (charging
monitoring unit) 18 is provided in the third power supply
unit 16 to detect a voltage inputted .to the third power
supply unit 16, i.e., a charging voltage of the buffer
capacitor 14a.
As illustrated in FIG. 20, the voltage detection unit
18 includes a Zener diode 18a, a transistor 18b and the like.
When the voltage inputted to the third power supply unit 16
exceeds the Zener voltage of the Zener diode 18a, the
transistor 18b is put in a conducting state such that a
detection signal indicating this status is inputted to the
control unit 13 (first pulse output unit 21). When
receiving the detection signal from the voltage detection
unit 18, the control unit 13 puts the main switching unit 11
in a conducting state (closed state) for a first
predetermined period. In FIGS. 18 and 20, the first pulse
output unit 21 is configured by hardware with a dedicated IC
and the like and is provided as a part of the control unit
13 to directly output the first pulse signal in response to
the detection signal from the voltage detection unit 18.
However, it is not limited thereto, and it may be configured
such that the output of the voltage detection unit 18 is
inputted to the main control part 20 including a CPU and the

like, and the first pulse signal is outputted by software.
It is preferable that the first predetermined period for
putting the main switching unit 11 in a conducting state is
set to be a time period slightly shorter than half cycle of
the commercial frequency power source.
Next, when an operation of putting the main switching
unit 11 in a non-conducting state (open state) is started
after the first predetermined period has elapsed, the
control unit 13 puts the auxiliary switching unit 17 in a
conducting state (closed state) only for a third
predetermined period (e.g., several hundred fx seconds).
This operation may be performed such that the auxiliary
switching unit 17 is put in a non-conducting state slightly
later than the main switching unit 11. Alternatively, a
pulse signal having a period longer by only the third
predetermined period than that of the first pulse signal
outputted from the main control part 20 to the main
switching unit 11 may be outputted to the auxiliary
switching unit 17. Alternatively, a delay circuit may be
configured by using a diode or capacitor.
By these operations, after the charging of the buffer
capacitor 14a is completed, power is supplied from the main
switching unit 11 to the load 3 for most of half cycle of
the commercial AC current. Then, after the conducting
current is reduced, power is supplied from the auxiliary
switching unit 17 to the load 3. Further, since the

auxiliary switching unit 17 has the auxiliary switch element
17a having a thyristor structure, the auxiliary switching
unit 17 is put in a non-conducting state (open state) when
the current value becomes zero (zero-cross point). When the
auxiliary switching unit 17 is put in a non-conducting state
(open state), since the current flows through the third
power supply unit 16 again, the above operations are
repeated every half cycle of the commercial AC power source.
In a case where a low load such as a miniature bulb is
connected to the load 3, the charging rate of the buffer
capacitor 14a is reduced and the charging is not completed
during half cycle of the power supply current. Accordingly,
a switching operation of the main switching unit 11
performed every half cycle may not be stabilized.
Accordingly, in the present invention, a standby time limit
is set to output a charging completion signal from the
voltage detection unit 18 when the first pulse output unit
21 makes the first pulse rise. That is, the first pulse
output unit 21 makes the first pulse rise after a
predetermined standby time limit has elapsed after receiving
a zero-cross detection signal from the zero-cross detection
unit 19.
FIG. 21 illustrates signal waveforms in respective
parts of the load control device ID in a high load. FIGS.
22 and 23 illustrate signal waveforms in respective parts of
the load control device ID in a low load. Further, FIG. 22

illustrates a case (comparison example) where the main
switching unit 11 is controlled while a standby time limit
is not set for the first pulse signal. FIG. 23 illustrates
a case (present embodiment) where the main switching unit 11
is controlled while a standby time limit is set for the
first pulse signal.
In a high load, i.e., when the connected load 3 has a
high capacity, as shown in FIG. 21, the buffer capacitor 14a
is charged for a short period. After the charging is
completed, power is supplied from the main switching unit 11
to the load 3 for most of half cycle of the commercial AC
power source. In this case, since the first predetermined
period is set to put the main switching unit 11 in a non-
conducting state before a time point (zero-cross point) when
the current value becomes zero, the main switching unit 11
is not put in a conducting state beyond the zero-cross point.
However, in a low load, i.e., when the connected load
3 has a low capacity, since the load current is small, a lot
of time is required for charging. Accordingly, as shown in
FIG. 22, the time from when the zero-cross detection unit 19
detects the zero-cross until the voltage detection unit 18
detects completion of the charging becomes long, and the
rise of the first pulse is delayed. Although the charging
of the buffer capacitor 14a is completed in a short period
of time after half cycle has elapsed after the zero-cross
detection unit 19 detects the zero-cross in FIG. 22, the

time longer than one cycle may be required for completion of
charging the buffer capacitor 14a. As described above, when
the rise of the first pulse is delayed, the start of
conduction of the main switching unit 11 is delayed.
Accordingly, the switching operation performed every half
cycle is not stabilized, and the lighting fluctuation occurs
in a miniature bulb connected as a load.
Accordingly, in the present invention, the standby
time limit is set to output a charging completion signal
from the voltage detection unit 18 when the first pulse
output unit 21 makes the first pulse rise. Specifically,
the first pulse output unit 21 makes the first pulse rise
after a predetermined standby time limit has elapsed after
receiving a zero-cross detection signal from the zero-cross
detection unit 19 as shown in FIG. 23. Further, the first
pulse output unit 21 receives the drop of the second pulse
outputted from the second pulse output unit 22 even before
the first predetermined period has elapsed, and makes the
first pulse drop. The first pulse signal outputted from the
first pulse output unit 21 is, as a main switching unit
drive signal, inputted to the drive circuit 10 to drive the
main switching unit 11.
Then, the third pulse output unit 23 having received
the first pulse signal outputs a third pulse signal for
putting the auxiliary switching unit 17 in a conducting
state only for a third predetermined period to the auxiliary

switching unit 17 when the main switching unit 11 is put in
a non-conducting state, and supplies power from the
auxiliary switching unit 17 to the load 3.
Further, in case of applying the voltage detection
unit 18 having the configuration shown in FIG. 20, a voltage
detection signal is not detected at the voltage detection
unit 18 during a time period until 1/2 cycle after 1/4 of
the power source cycle at which the current from the
alternating current power source is at a maximum level.
Accordingly, in order to suppress the delay of the start of
conduction of the main switching unit and stabilize the
operation, it is preferable to set the standby time limit to
be equal to or smaller than 1/4 of the power source cycle.
In the load control device ID in accordance with the
fourth embodiment of the present invention, when the voltage
detection unit 18 detects that the voltage inputted to the
third power supply unit 16 reaches a predetermined threshold,
the control unit 13 puts the main switching unit 11 in a
conducting state (closed state) for a first predetermined
period, and therefore, power is supplied from the main
switching unit 11 to the load for most of the half cycle of
the alternating current power source. Further, since there
is a limitation on the standby time for the start of
conduction of the main switching unit 11, for example, if it
is overly delayed for the voltage inputted to the third
power supply unit 16 in a low load to reach a predetermined

threshold, the main switching unit 11 is put in a conducting
state after the standby time limit. Accordingly, it is
possible to stably perform the switching operation of the
main switching unit 11 every half cycle, and prevent the
lighting fluctuation from occurring in a low load such as
miniature bulb lighting. Further, since the main switch
element lid having a transistor structure used in the main
switching unit 11 is in an active state in a low load, the
main switch element lid has a resistance. However, in the
low load, since the current flowing in the main switch
element lid becomes small, there is no excessive heating.
Further, when the main switching unit 11 is in a non-
conducting state after the first predetermined period, the
auxiliary switching unit 17 is put in a conducting state
only for a third predetermined period such that power is
supplied to the load 3 from the auxiliary switching unit 17.
Since these operations are performed with respect to the
load current, although the main switching unit 11 includes
the main switch element lid having a transistor structure,
it is possible to achieve a two-wire load control device
which is applicable to any one of a fluorescent lamp,
incandescent lamp and the like without being limited to
those having a power factor of 1. Further, it is possible
to suppress the noise generated in the operation of the load
control device to a low level, thereby achieving a load
control device having a small size and wide applicable load

range.
(Fifth Embodiment)
A load control device in accordance with a fifth
embodiment of the present invention will be described. FIG.
2 4 is a circuit diagram showing a configuration of a load
control device IE in accordance with the fifth embodiment of
the present invention. The load control device IE is
different from the load control device ID in accordance with
the fourth embodiment in that the load control device IE
further includes a current detection unit 26, and an OR
circuit 25b, and the other configuration of the load control
device IE is substantially the same as that of the load
control device ID. An AND circuit 25a is operated by a
first pulse signal outputted from a first pulse output unit
21 and a second pulse signal outputted from a second pulse
output unit 22. The current detection unit 2 6 detects the
current flowing into an auxiliary switching unit 17. The OR
circuit 25b is operated based on a signal outputted from the
current detection unit 2 6 and a signal outputted from the
AND circuit 25a.
The first pulse outputted from the first pulse output
unit 21 and the second pulse outputted from the second pulse
output unit 22 are inputted to the AND circuit 25a. The AND
circuit 25a calculates a logical product of the first pulse
and the second pulse and outputs the logical product to the
OR circuit 25b.

The auxiliary switching unit 17 is originally intended
to detect the zero-cross point of the current, not primarily
intended to provide electrical conduction, and is expected
to include a small-sized switch element. However, when the
frequency is deviated in the commercial AC power source, or
when the load control device is to be operated at both
frequencies of 50 Hz and 60 Hz, the time until the zero-
cross point of the current after the main switching unit is
put in a non-conducting state becomes long. Accordingly,
the electrical conduction in the auxiliary switching unit 17
is started before the load current becomes sufficiently
small. Further, in a case where an overload is connected as
the load, although the electrical conduction time of the
auxiliary switching unit 17 remains same, the electrical
conduction loss increases. Accordingly, the switch element
forming the auxiliary switching unit 17 may be broken.
Accordingly, in the fifth embodiment, the current flowing in
the auxiliary switching unit 17 is detected by the current
detection unit 26, and when the current exceeding an
allowable value flows in the auxiliary switching unit 17, a
main switching unit 11 is put in a conducting state (closed
state) again only for a short period (fourth predetermined
period). Then, when the main switching unit 11 is put in a
non-conducting state (open state), the auxiliary switching
unit 17 is put in a conducting state again.
Specifically, when the current detection unit 26

detects that a current exceeding the allowable value flows
in the auxiliary switching unit 17, it outputs a signal
indicating such status to the OR circuit 25b. When the OR
circuit 25b receives a signal outputted from the AND circuit
25a or a signal outputted from the current detection unit 26,
the OR circuit 25b puts the main switching unit 11 in a
conducting state only for a short period to protect the
auxiliary switching unit 17. As described above, by
repeatedly converting the main switching unit 11 and the
auxiliary switching unit 17, it is possible to prevent any
breakage in the switch element of the auxiliary switching
unit 17 and also to improve responsiveness with respect to
the type of the commercial AC power source or responsiveness
with respect to the overload.
In the load control device IE of the fifth embodiment,
when the current detection unit 26 detects that the current
exceeding the allowable value flows in the auxiliary
switching unit 17, the main switching unit is put in a
conducting state (closed state) and then put in a non-
conducting state. Accordingly, it is possible to prevent
the switch element of the auxiliary switching unit 17 from
being broken, and to form the auxiliary switching unit 17
using a small switch element. Thus, it is possible to
achieve miniaturization of the load control device, thereby
improving responsiveness with respect to the type of the
commercial AC power source or responsiveness with respect to

the overload.
(Sixth Embodiment)
A load control device in accordance with a sixth
embodiment of the present invention will be described. FIG.
25 is a circuit diagram showing a configuration of a load
control device IF in accordance with the sixth embodiment of
the present invention. Further, FIGS. 26 and 27 are time
charts showing waveforms of signals in respective parts of
the load control device IF.
The load control device IF of the sixth embodiment
shown in FIG. 25 connected in series between the AC power
source 2 and the load 3 includes a main switching unit 11 to
control the supply of power to a drive circuit 10 and the
load 3, a rectifying unit 12, and a control unit 13
controlling the entire load control device IF. The load
control device IF further includes a first power supply unit
14 which supplies a stable power to the control unit 13, a
second power supply unit 15 which supplies power to the
first power supply unit 14 when no power is supplied to the
load 3, and a third power supply unit 16 which supplies
power to the first power supply unit 14 when power is
supplied to the load 3. Also, the load control device IF
includes an auxiliary switching unit 17 which allows a
micro-current in the load current to flow therethrough, and
the like. The drive circuit 10 drives the main switching
unit 11 in response to a pulse signal outputted from the

control unit 13. Further, the third power supply unit 16
includes a voltage detection unit 18 which detects a voltage
inputted to the third power supply unit 16. The main
switching unit 11 has a main switch element lid (see FIG.
19) having a single gate transistor structure, and the
auxiliary switching unit 17 has an auxiliary switch element
17a having a thyristor structure. The voltage detection
unit 18 includes a Zener diode, transistor and the like.
When a voltage inputted to the third power supply unit 16
exceeds a Zener voltage of the Zener diode, the transistor
is put in a conducting state such that a detection signal
indicating such status is inputted to the auxiliary
switching unit 17. Further, the control unit 13 includes a
main control part 20 including a CPU and the like, and a
first pulse output unit 21. In FIG. 25, the first pulse
output unit 21 is configured by hardware with a dedicated IC
and the like. However, it is not limited thereto, and it
may be configured such that each pulse signal is outputted
by software from the main control part 20. [0050] (Invention
3)
Even in an OFF state of the load control device IF in
which no power is supplied to the load 3, a current flows in
the second power supply unit 15 from the power source 2
through the rectifying unit 12. Accordingly, although a
micro-current flows in the load 3, the current is suppressed
to a low level to avoid a malfunction in the load 3.

Accordingly, the impedance of the second power supply unit
15 is maintained at a high level.
When power is supplied to the load 3, the impedance of
the third power supply unit 16 is reduced and a current is
made to flow in the inner circuit of the load control device
IF such that a buffer capacitor 14a is charged. As
described above, the voltage detection unit (charging
monitoring unit) 18 is provided in the third power supply
unit 16 to detect a voltage inputted to the third power
supply unit 16, i.e., a charging voltage of the buffer
capacitor 14a.
As illustrated in FIG. 26, in a case where a high
capacity load is connected as the load 3, since the current
flowing in the third power supply unit 16 becomes larger,
the buffer capacitor 14a is charged for a short period.
Further, if the voltage detection unit 18 detects that a
voltage inputted to the third power supply unit 16 (i.e.,
terminal voltage of the buffer capacitor 14a) reaches a
predetermined threshold, a voltage detection signal is
inputted to the auxiliary switch element 17a of the
auxiliary switching unit 17 to put the auxiliary switching
unit 17 in a conducting state. The current flowing in the
auxiliary switching unit 17 is detected by a current
detection unit 26. If the current detection unit 26 detects
that the current flowing in the auxiliary switching unit 17
reaches a predetermined overcurrent threshold, the current

detection unit 26 outputs an overcurrent detection signal to
the first pulse output unit 21.
The auxiliary switching unit 17 is originally intended
to detect the zero-cross point of the current to thereby
surely cause the load current to become zero every half
cycle of the alternating current, but not primarily intended
to provide electrical conduction, and may be expected to
include a small-sized switch element. Accordingly, if the
current flowing in the auxiliary switching unit 17 becomes
excessive, the switch element forming the auxiliary
switching unit 17 may be broken. Accordingly, in the
present invention, the current flowing in the auxiliary
switching unit 17 is detected by the current detection unit
2 6, and when the high capacity load 3 is connected and the
current exceeding an allowable value flows in the auxiliary
switching unit 17, the conduction is converted from the
auxiliary switching unit 17 to the main switching unit 11 to
supply power to the load 3, thereby protecting the auxiliary
switching unit 17 from the overcurrent.
That is, the first pulse output unit 21 having
received the overcurrent detection signal immediately
outputs the first pulse signal for putting the main
switching unit 11 in a conducting state to the gate terminal
of the main switch element lid of the main switching unit 11.
After receiving the overcurrent detection signal, the first
pulse signal is outputted in a first predetermined period to

drive the main switching unit 11. As described above, the
main switching unit 11 is put in a conducting state and the
auxiliary switching unit 17 is put in a non-conducting state
to thereby protect the auxiliary switching unit 17 from the
overcurrent. Further, power is supplied from the main
switching unit 11 to the load 3 in the first predetermined
period, which is most of the half cycle of the commercial AC
power source. In this case, since the first predetermined
period is set to put the main switching unit 11 in a non-
conducting state before a time point (zero-cross point) when
the current value becomes zero, the main switching unit 11
is not put in a conducting state beyond the zero-cross point.
Meanwhile, in a case where a low capacity load is
connected as the load 3 as shown in FIG. 27, since the
current flowing in the auxiliary switching unit 17 does not
reach a predetermined overcurrent threshold, the main
switching unit 11 with large power consumption is not put in
a conducting state and the electrical conduction is
continuously performed by the auxiliary switching unit 17.
Further, the auxiliary switching unit 17 is put in a non-
conducting state at the next zero-cross point, and the
current flows into the third power supply unit 16 again.
Accordingly, the above operation is repeated every half
cycle of the commercial AC power source.
FIG. 28 illustrates a configuration example of the
current detection unit 2 6 applied to the load control device

IF in accordance with the sixth embodiment. In a case where,
e.g., a low capacity inverter is connected as the load 3,
the current passing through the current detection unit 26 is
small, but a peak value is large. In this case, if the
current detection unit 26 is configured to simply detect the
current value, conversion from the auxiliary switching unit
17 to the main switching unit 11 is frequently carried out,
and therefore, the power consumption may not be effectively
reduced. Accordingly, in this embodiment, as shown in FIG.
28, the current detection unit 26 is configured to include a
resistor 26e, an RC integrating circuit having a capacitor
26f, a transistor 26g and the like. The waveform of the
current passing through the auxiliary switching unit 17 is
attenuated to detect the energy of the passing current.
In the load control device IF in accordance with the
sixth embodiment of the present invention, in a high load,
if the voltage inputted to the third power supply unit 16
reaches a predetermined threshold, first, the control unit
13 puts the auxiliary switching unit 17 in a conducting
state (closed state). Then, if the current flowing in the
auxiliary switching unit 17 reaches a predetermined
overcurrent threshold, the control unit 13 puts the main
switching unit 11 in a conducting state. Accordingly, power
can be supplied from the main switching unit 11 to the load
for most of the half cycle of the alternating current power
source. Meanwhile, in a low load, since the current flowing

in the auxiliary switching unit 17 does not reach a
predetermined overcurrent threshold, the main switching unit
11 with large power consumption is not put in a conducting
state and the electrical conduction is performed by the
auxiliary switching unit 17. Thus, in case of applying,
e.g., an illumination apparatus as the load 3, it is
possible to reduce the power consumed in the load control
device when a miniature bulb is turned on.
Further, in case of applying the circuit shown in FIG.
28 as the current detection unit 26, the energy of the
current passing through the current detection unit 2 6 can be
detected by the RC integrating circuit. Accordingly, even
in a case where, e.g., a low capacity inverter is connected
as the load 3, wherein the current passing through the
auxiliary switching unit 17 is small, but a peak value is
large, it is possible to suppress frequent conduction
conversion to the main switching unit 11, thereby further
reducing the power consumption.
(Seventh Embodiment)
A load control device in accordance with a seventh
embodiment of the present invention will be described. FIG.
29 is a circuit diagram showing a configuration of a load
control device 1G in accordance with the seventh embodiment
of the present invention. Further, FIGS. 30 and 31 are time
charts showing waveforms of signals in respective parts of
the load control device 1G. The load control device 1G is

different from the load control device IF in accordance with
the sixth embodiment in that the load control device 1G
further includes a zero-cross detection unit 19, a second
pulse output unit 22, a third pulse output unit 23, an AND
circuit 25a, a current detection unit 26 and an OR circuit
25b, and the other configuration of the load control device
1G is substantially the same as that of the load control
device IF. FIG. 29 illustrates a configuration in which the
second pulse output unit 22 and the third pulse output unit
23 are configured by hardware with a dedicated IC and the
like. However, it is not limited thereto, and they may be
configured such that each pulse signal is outputted by
software from a main control part 20 including a CPU and the
like.
The zero-cross detection unit 19 detects a zero-cross
of a load current, and outputs a zero-cross detection signal
to the third pulse output unit 23. The second pulse output
unit 22 receives a voltage detection signal outputted from a
voltage detection unit 18, and outputs, as an auxiliary
switching unit drive signal, a second pulse signal for a
second predetermined period to an auxiliary switch element
17a of an auxiliary switching unit 17. The third pulse
output unit 23 receives the zero-cross detection signal
outputted from the zero-cross detection unit 19, and outputs
a third pulse signal for a third predetermined period to a
first pulse output unit 21 and the AND circuit 25a. The

first pulse output unit 21 receives an overcurrent detection
signal in the auxiliary switching unit 17 from the current
detection unit 26, and then outputs a first pulse to put a
main switching unit 11 in a conducting state only for a
first predetermined period, in the same way as the first
pulse output unit 21 of the sixth embodiment. Further, if
the charging completion of a buffer capacitor 14a is delayed,
when receiving the third pulse outputted from the third
pulse output unit 23 even before the first predetermined
period has elapsed, the first pulse output unit 21 makes the
first pulse drop.
The AND circuit 25a calculates a logical product of
the first pulse signal outputted from the first pulse output
unit 21 and the third pulse signal outputted from the third
pulse output unit 23 and outputs a logical product to the OR
circuit 25b. The OR circuit 25b calculates a logical sum of
the overcurrent detection signal outputted from the current
detection unit 2 6 and the signal outputted from the AND
circuit 25a, and outputs, as a main switching unit drive
signal, the logical sum to a drive circuit 10 and the second
pulse output unit 22.
As illustrated in FIG. 30, in a case where a high
capacity load is connected as the load 3, a buffer capacitor
14a is charged for a short period in the same way as in the
load control device IF of the sixth embodiment. Further, if
the voltage detection unit 18 detects that a voltage

inputted to a third power supply unit 16 reaches a charging
completion voltage, a voltage detection signal is outputted
to the second pulse output unit 22. The second pulse output
unit 22 having received the voltage detection signal outputs,
as an auxiliary switching unit drive signal, the second
pulse signal to the auxiliary switch element 17a of the
auxiliary switching unit 17 to put the auxiliary switching
unit 17 in a conducting state. Then, if the current
detection unit 2 6 detects that the current flowing in the
auxiliary switching unit 17 reaches a predetermined
overcurrent threshold, the current detection unit 26 outputs
an overcurrent detection signal to the first pulse output
unit 21.
The first pulse output unit 21 having received the
overcurrent detection signal outputs the first pulse signal
for putting the main switching unit 11 in a conducting state
to the AND circuit 25a. The first pulse signal outputted
from the first pulse output unit 21 and the third pulse
signal outputted from the third pulse output unit 23 are
inputted to the AND circuit 25a. The AND circuit 25a
calculates a logical product thereof, and outputs, as a main
switching unit drive signal, a logical product to the OR
circuit 25b. The main switching unit drive signal outputted
from the AND circuit 25a passes through the OR circuit 25b
and the drive circuit 10 and is inputted to the gate
terminal of a main switch element lid of the main switching

unit 11. Accordingly, the main switching unit 11 is put in
a conducting state while the first predetermined period
overlaps with the third predetermined period.
Further, the main switching unit drive signal
outputted from the AND circuit 25a passes through the OR
circuit 25b and is inputted to the second pulse output unit
22. The second pulse output unit 22 receives the drop of
the main switching unit drive signal indicating that the
main switching unit 11 is in a non-conducting state, and
outputs, as an auxiliary switching unit drive signal, the
second pulse to the auxiliary switch element 17a of the
auxiliary switching unit 17, thereby putting the auxiliary
switching unit 17 in a conducting state again. That is,
when an operation of putting the main switching unit 11 in a
non-conducting state (open state) is started after the first
predetermined period has elapsed, a control unit 13 puts the
auxiliary switching unit 17 in a conducting state only for a
second predetermined period (e.g., several hundred JJ.
seconds) . This operation may be performed such that the
auxiliary switching unit 17 is put in a non-conducting state
slightly later than the main switching unit 11. Further,
since the auxiliary switch element 17a has a thyristor
structure, the auxiliary switching unit 17 is put in a non-
conducting state at the next zero-cross point. When the
auxiliary switching unit 17 is put in a non-conducting state
(open state), a current flows into the third power supply

unit 16 again. Accordingly, the above operation is repeated
every half cycle of the commercial AC power source.
Meanwhile, as illustrated in FIG. 31, in a case where
a low capacity load is connected as the load 3, since the
current flowing in the auxiliary switching unit 17 does not
reach a predetermined overcurrent threshold, the main
switching unit 11 with large power consumption is not put in
a conducting state and the electrical conduction is
continuously performed by the auxiliary switching unit 17.
Further, the auxiliary switching unit 17 is put in a non-
conducting state at the next zero-cross point, and the
current flows into the third power supply unit 16 again.
Accordingly, the above operation is repeated every half
cycle of the commercial AC power source.
Further, in a case where a very low capacity load is
connected as the load 3, the charging rate of the buffer
capacitor 14a is reduced and the voltage detection signal
may not be outputted from the voltage detection unit 18
during half cycle of the commercial AC power source.
Accordingly, in this embodiment, there is a limitation on a
standby time during which the second pulse output unit 22
awaits the voltage detection signal outputted from the
voltage detection unit 18 . It may be configured such that
the second pulse is outputted from the second pulse output
unit 22 after the standby time limit is elapsed, regardless
of the presence of a voltage detection signal. With such

configuration, if it is overly delayed, for the voltage
inputted to the third power supply unit 16 to reach a
predetermined threshold, the auxiliary switching unit 17 is
put in a conducting state after the standby time limit.
Accordingly, it is possible to stably perform the switching
operation of the auxiliary switching unit 17 every half
cycle, and prevent the lighting fluctuation occurring in a
miniature bulb or the like.
As described above in the sixth embodiment, the
auxiliary switching unit 17 is originally intended to detect
the zero-cross point of the current, but not primarily
intended to provide electrical conduction, and may include a
small-sized switch element. However, when the frequency is
deviated in the commercial AC power source, or when the load
control device is to be operated at both frequencies of 50
Hz and 60 Hz, the time until the zero-cross point of the
current after the main switching unit is put in a non-
conducting state becomes long. Accordingly, the electrical
conduction of the auxiliary switching unit is started before
the load current becomes sufficiently small. Further, in a
case where an overload is connected as the load 3, although
the electrical conduction time of the auxiliary switching
unit 17 remains to be same, the electrical conduction loss
increases. Accordingly, the switch element forming the
auxiliary switching unit 17 may be broken.
Accordingly, in the seventh embodiment, in FIG. 30,

even when the operation of the main switching unit 11 is
converted into the operation of the auxiliary switching unit
17, the current flowing in the auxiliary switching unit 17
is detected by the current detection unit 26, and when a
current exceeding an allowable value is found to flow in the
auxiliary switching unit 17, the main switching unit 11 is
put in a conducting state (closed state) again only for a
short period (fourth predetermined period). Then, when the
main switching unit 11 is put in a non-conducting state
(open state) , the auxiliary switching unit 17 is put in a
conducting state again.
Specifically, the current detection unit 26 which
detects that the current exceeding the allowable value flows
in the auxiliary switching unit 17 outputs the overcurrent
detection signal to the OR circuit 25b. When the OR circuit
25b receives a signal outputted from the AND circuit 25a or
a signal outputted from the current detection unit 26, the
OR circuit 25b puts the main switching unit 11 in a
conducting state only for a short period to protect the
auxiliary switching unit 17. As described above, by
repeatedly converting the main switching unit 11 and the
auxiliary switching unit 17, it is possible to prevent
breakage in the switch element of the auxiliary switching
unit 17.
In the load control device 1G in accordance with the
seventh embodiment of the present invention, after the third

predetermined period, that is shorter than the half cycle,
from the detection of the zero-cross point of the load
current, the main switching unit 11 is put in a non-
conducting state. Accordingly, for example, in a low load,
although a timing of starting the conduction of the main
switching unit 11 is delayed due to the late charging
completion of the buffer capacitor 14a, the main switching
unit 11 can be surely put in a non-conducting state before
the load current becomes zero. Accordingly, the main
switching unit 11 is not put in a conducting state beyond
the zero-cross point, and the operation of the load control
device performed every half cycle is stabilized. Further,
when the main switching unit 11 is put in a non-conducting
state, the auxiliary switching unit 17 is put in a
conducting state only for a predetermined period.
Accordingly, in a high load, after power is supplied to the
load 3 from the main switching unit 11 for most of the half
cycle of the commercial AC power source, the electrical
conduction current is reduced, and then, power is supplied
to the load from the auxiliary switching unit 17. Since
these operations are performed with respect to the load
current, although the main switching unit 11 includes a
switch element having a transistor structure, it is possible
to achieve a two-wire load control device which is
applicable to any one of a fluorescent lamp, incandescent
lamp and the like without being limited to those having a

power factor of 1. Further, it is possible to suppress the
noise generated in the operation of the load control device
to a low level, thereby achieving a load control device
having a small size and wide applicable load range.
Further, when the current detection unit 26 detects
that a current exceeding the allowable value flows in the
auxiliary switching unit 17, the main switching unit 11 is
put in a conducting state (closed state) and then put in a
non-conducting state. Accordingly, it is possible to
prevent the switch element of the auxiliary switching unit
17 from being broken, and to form the auxiliary switching
unit 17 using a small switch element. Thus, it is possible
to achieve miniaturization of the load control device,
thereby improving responsiveness with respect to the type of
the commercial AC power source or responsiveness with
respect to the overload.
(Eighth Embodiment)
A load control device in accordance with an eighth
embodiment of the present invention will be described. FIG.
32 is a circuit diagram showing a configuration of a load
control device 1H in accordance with the eighth embodiment
of the present invention. Further, FIGS. 33 and 34 are time
charts showing waveforms of signals in respective parts of
the load control device 1H.
The load control device 1H of the eighth embodiment
shown in FIG. 32 connected in series between the AC power

source 2 and the load 3 includes a main switching unit 11 to
control the supply of a power to a drive circuit 10 and the
load 3, a rectifying unit 12, and a control unit 13
controlling the entire load control device 1H. The load
control device 1H further includes a first power supply unit
14 which supplies a stable power to the control unit 13, a
second power supply unit 15 which supplies power to the
first power supply unit 14 when no power is supplied to the
load 3, and a third power supply unit 16 which supplies
power to the first power supply unit 14 when power is
supplied to the load 3. Also, the load control device 1H
includes an auxiliary switching unit 17 which allows a
micro-current in the load current to flow therethrough, an
AND circuit 27, a manipulation unit 28 manipulated by a user,
and the like. The drive circuit 10 drives the main
switching unit 11 in response to a pulse signal outputted
from the control unit 13. Further, the third power supply
unit 16 includes a voltage detection unit 18 which detects a
voltage inputted to the third power supply unit 16, and a
zero-cross detection unit 19 which detects a zero-cross
point of the load current. The main switching unit 11 has a
main switch element lid (see FIG. 19) having a single gate
transistor structure, and the auxiliary switching unit 17
has an auxiliary switch element 17a having a thyristor
structure. Further, the control unit 13 includes a main
control part 20 including a CPU and the like, a first pulse

output unit 21, a second pulse output unit 22, and a dimming
control pulse output unit 24.
The main control part 20 sets a main switching unit
conducting time which is counted in order to put the main
switching unit 11 in a conducting state in the half cycle of
an alternating current power source in response to a
manipulation inputted to the manipulation unit 28. The main
control part 20 controls the drive circuit 10 by counting
the main switching unit conducting time through the dimming
control pulse output unit 24, thereby intermittently
controlling the current flowing in the load 3. After
receiving the charging completion signal of a buffer
capacitor 14a from the voltage detection unit 18, the first
pulse output unit 21 outputs a first pulse to put the main
switching unit 11 in a conducting state only for a first
predetermined period. That is, the first pulse rises when
receiving the charging completion signal from the voltage
detection unit 18, and drops after the first predetermined
period.
After detecting that the main switching unit 11 is put
in a non-conducting state (open state), the second pulse
output unit 22 outputs a second pulse signal for a
predetermined period to put the auxiliary switching unit 17
in a conducting state only for a second predetermined period.
That is, the second pulse rises when detecting that the main
switching unit 11 is put in a non-conducting state (open

state), and drops after the second predetermined period.
The dimming control pulse output unit 24 counts the main
switching unit conducting time set by the main control part
20 and outputs a dimming control pulse to the AND circuit 27.
The manipulation unit 28 is manipulated by the user to
adjust the current flowing in the load 3. The manipulation
unit 28 is provided with a volume switch to allow the user
to adjust the current flowing in the load 3 and the like.
In a case where, e.g., an illumination apparatus is
connected as the load 3, the user may perform dimming by '
manipulating the manipulation unit 28. Further, similarly,
in a case where a driving motor of a ventilation fan is
connected as the load 3, the user may adjust an air volume
by manipulating the manipulation unit 28.
Even in an OFF state of the load control device 1H in
which no power is supplied to the load 3, a current flows in
the second power supply unit 15 from the power source 2
through the rectifying unit 12. Accordingly, although a
micro-current flows in the load 3, the current is suppressed
to a low level to avoid a malfunction in the load 3.
Accordingly, the impedance of the second power supply unit
15 is maintained at a high level.
When power is supplied to the load 3, the impedance of
the third power supply unit 16 is reduced and the current is
made to flow in the inner circuit of the load control device
1H, thereby charging the buffer capacitor 14a. As described

above, the voltage detection unit (charging monitoring unit)
18 is provided in the third power supply unit 16 to detect a
voltage inputted to the third power supply unit 16, i.e., a
charging voltage of the buffer capacitor 14a. When the
charging of the buffer capacitor 14a is completed, the third
power supply unit 16 is turned off. Then, in
synchronization with the operation of the main switching
unit 11, the third power supply unit 16 is turned on again
while lowering the impedance.
The voltage detection unit 18 includes, e.g., a Zener
diode, a transistor and the like. When the voltage inputted
to the third power supply unit 16 exceeds a Zener voltage of
the Zener diode, the transistor is put in a conducting state
such that a detection signal indicating this status is
inputted to the control unit 13 (first pulse output unit 21).
In a normal operation, when receiving the detection signal
from the voltage detection unit 18, the control unit 13 puts
the main switching unit 11 in a conducting state (closed
state) for a first predetermined period. In FIG. 32, the
first pulse output unit 21 is configured by hardware with a
dedicated IC and the like and is provided as a part of the
control unit 13 to directly output the first pulse signal in
response to the detection signal from the voltage detection
unit 18. However, it is not limited thereto, and it may be
configured such that the output of the voltage detection
unit 18 is inputted to the main control part 20 including a

CPU and the like, and the first pulse signal is outputted by
software. It is preferable that the first predetermined
period for putting the main switching unit 11 in a
conducting state is set to be a time period slightly shorter
than half cycle of the commercial AC frequency power source.
Next, when an operation of putting the main switching
unit 11 in a non-conducting state (open state) is started
after the first predetermined period has elapsed, the
control unit 13 puts the auxiliary switching unit 17 in a
conducting state (closed state) only for a second
predetermined period (e.g., several hundred fx seconds).
This operation may be performed such that the auxiliary
switching unit 17 is put in a non-conducting state slightly
later than the main switching unit 11. Alternatively, a
pulse signal having a period longer by only the second
predetermined period than that of the first pulse signal
outputted from the main control part 20 to the main
switching unit 11 may be outputted to the auxiliary
switching unit 17. Alternatively, a delay circuit may be
configured by using a diode or capacitor.
By these operations, after the charging of the buffer
capacitor 14a is completed, power is supplied from the main
switching unit 11 to the load 3 for most of half cycle of
the commercial AC current. Then, after the conducting
current is reduced, power is supplied from the auxiliary
switching unit 17 to the load 3. Further, since the

auxiliary switching unit 17 has the auxiliary switch element
17a having a thyristor structure, the auxiliary switching
unit 17 is put in a non-conducting state (open state) when
the current value becomes zero (zero-cross point). When the
auxiliary switching unit 17 is put in a non-conducting state
(open state), since the current flows into the third power
supply unit 16 again, the above operations are repeated
every half cycle of the commercial AC power source.
FIG. 33 illustrates waveforms of signals in respective
parts of the load control device 1H in a normal operation.
FIG. 34 illustrates waveforms of signals in respective parts
of the load control device 1H in a dimming operation. In
the normal operation, i.e., when dimming of the illumination
apparatus serving as the load 3 is not performed, as
illustrated in FIG. 33, a high signal is always outputted
from the dimming control pulse output unit 24. Accordingly,
after the charging of the buffer capacitor 14a is completed,
power is supplied from the main switching unit 11 to the
load 3 for most of half cycle of the commercial AC power
source. In this case, since the first predetermined period
is set to put the main switching unit 11 in a non-conducting
state before a time point (zero-cross point) when the
current value becomes zero, the main switching unit 11 is
not put in a conducting state beyond the zero-cross point.
Then, the second pulse output unit 22 having received
the first pulse signal outputs the second pulse signal for

putting the auxiliary switching unit 17 in a conducting
state only for a second predetermined period to the
auxiliary switching unit 17 when the main switching unit 11
is put in a non-conducting state, such that power is
supplied from the auxiliary switching unit 17 to the load 3.
Meanwhile, in the dimming operation, i.e., when the
manipulation unit 28 is manipulated by the user to perform
dimming of the illumination apparatus serving as the load 3,
as shown in FIG. 34, a dimming control pulse signal is
outputted from the dimming control pulse output unit 24.
The dimming control pulse signal has a low signal outputted
in the main switching unit non-conducting time and a high
signal outputted in the main switching unit conducting time.
The main switching unit non-conducting time is counted after
the zero-cross detection unit 19 detects the zero-cross
point. The main switching unit conducting time is
continuously counted after counting the main switching unit
non-conducting time.
The dimming control pulse signal outputted from the
dimming control pulse output unit 24 is inputted to the AND
circuit 27. The AND circuit 27 calculates a logical product
of the first pulse outputted from the first pulse output
unit 21 and the dimming control pulse signal outputted from
the dimming control pulse output unit 2 4 to generate a main
switching unit drive signal, and outputs the main switching
unit drive signal to the main switching unit 11 through the

drive circuit 10. Accordingly, the main switching unit 11
is put in a conducting state only while the first
predetermined period, which is counted from when the voltage
detection unit 18 detects that the voltage inputted to the
third power supply unit 16 reaches a predetermined threshold,
overlaps with the main switching unit conducting time, which
is counted from when the zero-cross detection unit 19
detects the zero-cross. The current flowing in the load 3
is intermittently controlled to perform dimming of the load
3. Further, since the subsequent operations of the second
pulse output unit 22 and the auxiliary switching unit 17 are
the same as those in the normal operation, a description
thereof will be omitted.
In the load control device 1H in accordance with the
eighth embodiment of the present invention, in the normal
operation, when the voltage detection unit 18 detects that
the voltage inputted to the third power supply unit 16
reaches a predetermined threshold, since the control unit 13
puts the main switching unit 11 in a conducting state
(closed state) for a first predetermined period, power is
supplied from the main switching unit 11 to the load for
most of the half cycle of the alternating current power
source. Further, in the dimming operation, since the
conduction of the main switching unit 11 is intermittently
controlled by the manipulation inputted to the manipulation
unit 28, it is possible to reduce the power consumption by

performing a desired operation on the load by using the two-
wire load control device. For example, in a case where the
load 3 is an illumination apparatus, the user may manipulate
the manipulation unit 28 such that dimming is performed at a
desired brightness level. Further, after the zero-cross
detection unit 19 detects the zero-cross point, the main
switching unit non-conducting time is counted, and then the
main switching unit conducting time is counted. Accordingly,
by appropriately setting the main switching unit non-
conducting time, it may be configured such that the time
until the voltage inputted to the third power supply unit 16
reaches a predetermined threshold does not overlap with the
main switching unit conducting time. Accordingly, the
intermittent conduction control of the load may be performed
accurately in response to the operation of the user.
Further, since the main switch element lid of the main
switching unit 11 has a transistor structure, it is possible
to achieve miniaturization of the load control device
generating less noise and less heat.
Further, when the main switching unit 11 is put in a
non-conducting state after the first predetermined period,
the auxiliary switching unit 17 is put in a conducting state
only for the third predetermined period to supply power from
the auxiliary switching unit 17 to the load 3. Accordingly,
although a transistor is used as the main switch element lid
of the main switching unit 11, it is possible to achieve a

phase control not requiring an interruption of the current.
Further, the noise generated in the operation of the load
control device can be suppressed at a low level, and the
switching loss becomes small, thereby achieving a small-
sized apparatus.
(Ninth Embodiment)
A load control device in accordance with a ninth
embodiment of the present invention will be described. FIG.
35 is a circuit diagram showing a configuration of a load
control device II in accordance with the ninth embodiment of
the present invention. Further, FIGS. 36 and 37 are time
charts showing waveforms of signals in respective parts of
the load control device II. The load control device II is
different from the load control device 1H in accordance with
the eighth embodiment in that the load control device II
further includes a third pulse output unit 23, an AND
circuit 25a, a current detection unit 26 and an OR circuit
25b, and the other configuration of the load control device
II is substantially the same as that of the load control
device IF.
In a case where a low capacity load such as a
miniature bulb is connected as the load 3, since the load
current is small, a lot of time is required for charging a
buffer capacitor 14a. Accordingly, the time from when a
zero-cross detection unit 19 detects the zero-cross until a
voltage detection unit 18 detects completion of the charging

becomes long, and the rise of the first pulse is delayed.
The first predetermined period is set considering the above-
described case where the high capacity load is connected.
Accordingly, if the rise of the first pulse is overly
delayed, the first pulse drops after the load current
exceeds the zero-cross point. Thus, in a case where a main
switching unit 11 is controlled by using only ' the first
pulse and the dimming control pulse, in a low load, the main
switching unit 11 is put in a conducting state beyond the
zero-cross point, and the charging operation every half
cycle is not stabilized.
Accordingly, in this embodiment, as shown in FIGS. 36
and 37, the open state of the main switching unit 11 is
limited to a third predetermined period by using a third
pulse outputted from the third pulse output unit 23. The
third pulse output unit 23 outputs the third pulse such that
the open state of the main switching unit 11 is limited to a
third predetermined period after the zero-cross detection
unit 19 has detected a zero-cross point of the power supply
current. That is, the third pulse rises when receiving a
zero-cross detection signal from the zero-cross detection
unit 19, and drops after the third predetermined period that
is shorter than the half cycle of the load current. The AND
circuit 25a calculates a logical product of the first pulse
signal outputted from a first pulse output unit 21 and the
third pulse signal outputted from the third pulse output

unit 23 and outputs a logical product to a AND circuit 27.
The OR circuit 25b calculates a logical sum of the signal
outputted from the current detection unit 2 6 and the signal
outputted from the AND circuit 27 to generate a main
switching unit drive signal, and outputs the main switching
unit drive signal to the main switching unit 11 through a
drive circuit 10.
By these operations, the main switching unit 11 is put
in a closed state only while the first predetermined period
during which the first pulse rises, the third predetermined
period during which the third pulse rises, and the main
switching unit conducting time during which the dimming
control pulse rises overlap with each other. As described
above, since the third pulse rises at a timing when the
zero-cross detection unit 19 detects the zero-cross point,
and drops in the third predetermined period, being shorter
than the half cycle of the load current, although the timing
of detecting the charging completion of the buffer capacitor
14a, i.e., the timing of starting the first predetermined
period is deviated later, the main switching unit 11 is not
in a closed state beyond the zero-cross point of the power
supply frequency. Accordingly, it is possible to surely
perform charging every half cycle, thereby stabilizing the
operation.
Further, an auxiliary switching unit 17 is originally
intended to detect the zero-cross point of the current, not

primarily intended to provide electrical conduction, and may
include a small-sized switch element. However, when the
frequency is deviated in the commercial AC power source, or
when the load control device is to be operated at both
frequencies of 50 Hz and 60 Hz, the time until the zero-
cross point of the current after the main switching unit is
put in a non-conducting state becomes long. Accordingly,
the electrical conduction of the auxiliary switching unit is
started before the load current becomes sufficiently small.
Further, in a case where an overload is connected as the
load, although the electrical conduction time of the
auxiliary switching unit remains to be same, the electrical
conduction loss increases. Accordingly, the switch element
forming the auxiliary switching unit 17 may be broken.
Accordingly, in the ninth embodiment, the current flowing in
the auxiliary switching unit 17 is detected by the current
detection unit 26, and when the current exceeding an
allowable value is found to flow in the auxiliary switching
unit 17, the main switching unit 11 is put in a conducting
state (closed state) again only for a short period (fourth
predetermined period). Then, when the main switching unit
11 is put in a non-conducting state (open state) , the
auxiliary switching unit 17 is put in a conducting state
again.
Specifically, the current detection unit 26 which
detects that the current exceeding the allowable value flows

in the auxiliary switching unit 17 outputs a signal
indicating such status to the OR circuit 25b. When the OR
circuit 25b receives a signal outputted from the AND circuit
25a or a signal outputted from the current detection unit 26,
the OR circuit 25b puts the main switching unit 11 in a
conducting state only for a short period to protect the
auxiliary switching unit 17. As described above, by
repeatedly converting the main switching unit 11 and the
auxiliary switching unit 17, it is possible to prevent
breakage of an auxiliary switch element 17a of the auxiliary
switching unit 17 and also to improve responsiveness with
respect to the type of the commercial AC power source or
responsiveness with respect to the overload.
In the load control device II of the ninth embodiment,
after the third predetermined period has elapsed even in the
first predetermined period, a control unit 13 puts the main
switching unit 11 in a non-conducting state. Accordingly,
for example, in a low load, although a timing of starting
the first predetermined period is delayed, the main
switching unit 11 is put in a non-conducting state before
the load current becomes zero. Accordingly, since the main
switching unit 11 is not put in a conducting state beyond
the zero-cross point of the load current, charging can be
surely performed during the half cycle of the AC power
source, and the operation performed every half cycle can be
stabilized. Further, when the current detection unit 26

detects that the current exceeding the allowable value flows
in the auxiliary switching unit 17, the main switching unit
is put in a conducting state (closed state) and then put in
a non-conducting state. Accordingly, it is possible to
prevent the switch element of the auxiliary switching unit
17 from being broken, and to form the auxiliary switching
unit 17 by using a small switch element. Thus, it is
possible to achieve miniaturization of the load control
device, thereby improving responsiveness with respect to the
type of the commercial AC power source or responsiveness
with respect to the overload.
Further, in the load control devices ID to II in
accordance with the fourth to ninth embodiments of the
present invention, the configurations of the main switch
element and the drive circuit thereof are not limited to the
above-described embodiments, and the modification examples
of the above-described embodiments may be applied. For
example, as the main switch element having a dual gate
transistor structure shown in FIG. 5A and the drive circuit
thereof, the drive circuit 10 shown in FIG. 12 or the
modification example of the drive circuit 10 of FIG. 12,
which is shown in FIG. 13, may be applied to the above
embodiments. FIG. 38 illustrates a longitudinal cross-
sectional configuration of the main switch element having a
lateral dual gate transistor structure, which is a
bidirectional element that can reduce its loss by providing

a withstand voltage maintaining region at one location. In
this configuration, it is possible to reduce the amount of
heat generated by the main switch element when power is
supplied to the load 3, thereby achieving both
miniaturization and high capacity of the load control device.
Further, instead of the drive circuit 10 shown in FIG.
12, the drive circuit 10 shown in FIG. 14 may be applied to
the drive circuit of the above embodiments.
Further, instead of the drive circuit 10 shown in FIG.
12, the drive circuit 10 shown in FIG. 8 and the detailed
configuration example or the modification example of the
drive circuit of FIG. 8, which is shown in FIG. 9, 10, or 11,
may be applied to the above embodiments.
(Tenth to Twelfth Embodiments)
Next, load control devices in accordance with the
tenth to twelfth embodiments of the present invention will
be described. The load control device using a drive circuit
10 shown in FIGS. 8 to 11 has a circuit configuration in
which no current is allowed to flow by a diode of a
rectifying unit 12 when a drive signal is applied to a main
switch element lid of a main switching unit 11. Accordingly,
an operation may be performed only for a voltage type
element in which a gate (gate terminal) of a main switch
element lid does not require a current value equal to or
greater than a predetermined value. However, in the tenth
to twelfth embodiments, a stable operation may be performed

even for a current type element in which the main switch
element lid of the main switching unit 11 requires a current
value equal to or greater than a predetermined value.
As illustrated in FIGS. 39, 40 and 41, in load control
devices 1J, IK and 1L in accordance with the tenth to
twelfth embodiments, synchronous switching elements 220a and
220b are connected between the AC line of the rectifying
unit 12 and the minus side output of the rectifying unit 12
serving as a basis of the circuit, and synchronous switching
elements 220a and 220b are turned on in synchronization with
an operation of putting the main switching unit 11 in a
closed state. When the synchronous switching elements 220a
and 220b are closed in synchronization with an operation of
putting the main switching unit 11 in a closed state, a path
is formed to flow the current through the gate of the main
switch element lid of the main switching unit 11 from a
first power supply unit 14 in the load control devices 1J,
IK and 1L. Accordingly, a stable operation may be performed
even if the gate of the main switch element lid is a dual
gate element requiring a current. Further, the other
configurations or basic operations of the load control
devices 1J, IK and 1L are substantially the same as those of
the load control devices ID to II using the drive circuit 10
shown in FIGS. 8 to 11. Further, the configuration of the
drive circuit 10 is not particularly limited, and may adopt
the basic configuration of the load control device or each

modification example.
(Thirteenth to Fifteenth Embodiments)
Next, load control devices in accordance with the
thirteenth to fifteenth embodiments of the present invention
will be described. The load control devices in accordance
with the thirteenth to fifteenth embodiments are different
from the load control devices in accordance with the tenth
to twelfth embodiments in that a drive circuit 10 shown in
FIG. 42 is used instead of the drive circuits 10 shown in
FIGS. 39, 40 and 41.
In the load control devices in accordance with the
thirteenth to fifteenth embodiments, the drive circuit 10 of
a main switching unit 11 includes high withstand voltage
diodes 301a and 301b connected to a first power supply unit
14 of the load control device, capacitors 302a and 302b
having one ends connected to respective power lines and the
other ends connected to the diodes 301a and 301b, and self-
arc extinction type drive switch elements 305a and 305b such
as photothyristors and phototriacs connected between gate
terminals of a main switch element lid of the main switching
unit 11 and connection points between the diodes 301a and
301b and the capacitors 302a and 302b.
In the thirteenth and fifteenth embodiments, when the
charging completion detection is performed by a voltage
detection unit 18 provided in a third power supply unit 16,
the main switching unit 11 is put in a closed state. In the

fourteenth embodiment, when the overcurrent detection is
performed by a current detection unit 2 6 connected to an
auxiliary switching unit 17, the main switching unit 11 is
put in a closed state. In this case, a signal is inputted
to put the drive switch elements 305a and 305b connected to
the gate electrodes of the main switch element lid of the
main switching unit 11. However, since each of the drive
switch elements 305a and 305b has a thyristor or triac
structure, each of the drive switch elements 305a and 305b
may be driven only by a trigger signal. Accordingly, the
driving power of each of the drive switch elements 305a and
305b may be smaller than that in each of the above-described
embodiments. Further, each of the drive switch elements
305a and 305b may be in a non-conducting state only by
opening a corresponding one of the synchronous switching
elements 220a and 220b provided in a rectifying unit 12,
thereby reducing the driving power for opening/closing the
main switching unit 11. In the two-wire load control device,
since it is an important object to enable load control while
stably ensuring a power supply, it is preferable in the
stable operation of the load that the driving power of the
load control device is small.
The present invention is not limited to the
configurations of the above-described embodiments, and may
be applied to a load control device using a MOSFET element
or other switch element.

Further, the present invention is not limited to the
configurations of the above-described embodiments, and may
be configured to control the main switching unit 11 at least
such that when power is supplied to the load, a main
switching unit drive signal rises if the voltage detected by
the voltage detection unit 18 does not reach a predetermined
threshold within the standby time limit, and the main
switching unit drive signal is started after a predetermined
period shorter than the half cycle of the load current after
a zero-cross detection unit 19 detects a zero-cross point of
the load current.
Further, the present invention is not limited to the
configurations of the above-described embodiments, and may
be configured at least such that when power is supplied to
the load, the auxiliary switching unit 17 is first in a
conducting state if the voltage detection unit 18 detects
that the voltage inputted to the third power supply unit 16
reaches a predetermined threshold; the main switching unit
11 is then in a conducting state if the current detection
unit 2 6 detects that the current flowing in the auxiliary
switching unit 17 reaches a predetermined threshold; and the
auxiliary switching unit 17 is continuously in a conducting
state if the current flowing in the auxiliary switching unit
17 does not reach a predetermined threshold.
Further, the present invention is not limited to the
configurations of the above-described embodiments, and may

be configured to control dimming at least such that the main
switching unit conducting time counted to put the main
switching unit 11 in a conducting state during the half
cycle of the AC power source is set in response to the
manipulation inputted to a manipulation unit 28, and the
main switching unit 11 is put in a conducting state only
while the first predetermined period, which is counted from
when the voltage detection unit 18 detects that the voltage
inputted to the third power supply unit 16 reaches a
predetermined threshold, overlaps with the main switching
unit conducting time. Further, the present invention can be
variously modified, and for example, the output of the zero-
cross detection unit 19 may be inputted to a main control
part 20 including a CPU and the like to thereby output the
second pulse in software.
While the invention has been shown and described with
respect to the embodiments, it will be understood by those
skilled in the art that various changes and modification may
be made without departing from the scope of the invention as
defined in the following claims.

We Claim:.
1. A two-wire load control device connected in series
between an alternating current (AC) power source and a load,
comprising:
a main switching unit which has a main switch element
connected in series to the AC power source and the load, and
controls a supply of power to the load;
a manipulation switch which is manipulated by a user,
and outputs a start-up signal for starting at least the
load;
a control unit which is connected to the manipulation
switch and controls opening/closing of the main switching
unit based on a signal transmitted from the manipulation
switch;
a first power supply unit, to which power is supplied
from both terminals of the main switching unit through a
rectifying unit, for supplying a stable voltage to the
control unit;
a second power supply unit, to which power is supplied
from both terminals of the main switching unit through the
rectifying unit, for supplying power to the first power
supply unit no power is supplied to the load; and
a third power supply unit for supplying power to the
first power supply unit when power is supplied to the load
in a closed state of the main switching unit,

wherein upon receiving the start-up signal from the
manipulation switch, the control unit outputs an initial
drive signal for putting the main switch element in a
conducting state to the main switching unit before a power
source for supplying power to the first power supply unit is
switched from the second power supply unit to the third
power supply unit.
2. The load control device of claim 1, wherein the main
switch element is a triac, and the initial drive signal is a
pulse signal having a predetermined pulse width, the pulse
signal being inputted to a gate of the triac.
3. The load control device of claim 1, wherein the main
switch element is an element having a transistor structure,
and the initial drive signal is a pulse signal having a
pulse width equal to or larger than 1/4 cycle of the
commercial AC power source and smaller than 1/2 cycle of the
commercial AC power source, the pulse signal being inputted
to a gate of the transistor structure.
4. The load control device of claim 3, further comprising
an auxiliary switching unit which includes an auxiliary
switch element" having a thyristor structure, and controls
the supply of power to the load when the main switching unit
is in a non-conducting state.

5. The load control device of claim 4, further
comprising:
a buffer capacitor which supplies power to the first
power supply unit when any of the second power supply unit
and the third power supply unit fails to supply power to the
first power supply unit; and
a voltage detection unit which detects an input
voltage of the third power supply unit or a terminal voltage
of the buffer capacitor when power is supplied to the load
in the closed state of the main switching unit,
wherein when power is supplied to the load, the
control unit outputs a first pulse signal for putting the
main switching unit in a conducting state for a
predetermined period to the main switching unit if the
voltage detection unit detects that the input voltage of the
third power supply unit or the terminal voltage of the
buffer capacitor reaches a predetermined threshold, and
outputs a second pulse signal for putting the auxiliary
switching unit in a conducting state when the main switching
unit is put in a non-conducting state by absence of the
first pulse signal.
6. A two-wire load control device connected in series
between an AC power source and a load, comprising:
a main switching unit which includes a switch element

having a transistor structure, and controls a supply of
power to the load;
an auxiliary switching unit which includes a switch
element having a thyristor structure, and controls the
supply of power to the load when the main switching unit is
in a non-conducting state;
a control unit which controls opening/closing of the
main switching unit and the auxiliary switching unit;
a first power supply unit, to which power is supplied
from both terminals of the main switching unit through a
rectifying unit, for supplying a stable voltage to the
control unit;
a second power supply unit, to which power is supplied
from both terminals of the main switching unit through the
rectifying unit, for supplying power to the first power
supply unit when no power is supplied to the load;
a third power supply unit for supplying power to the
first power supply unit when power is supplied to the load
in a closed state of the main switching unit or the
auxiliary switching unit;
a voltage detection unit which detects a voltage
inputted to the third power supply unit; and
a zero-cross detection unit which detects a zero-cross
point of a load current,
wherein when power is supplied to the load, the
control unit causes a rise of a main switching unit drive

signal for putting the main switching unit in a conducting
state if the voltage detection unit detects that the voltage
inputted to the third power supply unit reaches a
predetermined threshold within a predetermined standby time
limit after the zero-cross detection unit detects the zero-
cross point of the load current, and starts supplying the
main switching unit drive signal after a predetermined
period, that is shorter than half cycle of the load current,
after the zero-cross detection unit detects the zero-cross
point of the load current, and
wherein when power is supplied to the load, the
control unit causes a rise of the main switching unit drive
signal after the standby time limit is elapsed if the
voltage detection unit fails to detect that the voltage
inputted to the third power supply unit reaches a
predetermined threshold within the standby time limit, and
starts supplying the main switching unit drive signal after
a predetermined period, that is shorter than half cycle of
the load current, after the zero-cross detection unit
detects the zero-cross point of the load current.
7. The load control device of claim 6, wherein the
standby time limit is equal to or smaller than 1/4 of a
power source cycle.
8. A two-wire load control device connected in series

between an AC power source and a load, comprising:
a main switching unit which includes a switch element
having a transistor structure, and controls a supply of
power to the load;
an auxiliary switching unit which includes a switch
element having a thyristor structure, and controls the
supply of power to the load when the main switching unit is
in a non-conducting state;
a control unit which controls opening/closing of the
main switching unit and the auxiliary switching unit;
a first power supply unit, to which power is supplied
from both terminals of the main switching unit through a
rectifying unit, for supplying a stable voltage to the
control unit;
a second power supply unit, to which power is supplied
from both terminals of the main switching unit through the
rectifying unit, for supplying power to the first power
supply unit when no power is supplied to the load;
a third power supply unit for supplying power to the
first power supply unit when power is supplied to the load
in a closed state of the main switching unit or the
auxiliary switching unit;
a voltage detection unit which detects a voltage
inputted to the third power supply unit; and
a current detection unit which detects a current
flowing into the auxiliary switching unit,

wherein when power is supplied to the load, the
auxiliary switching unit is put in a conducting state if the
voltage detection unit detects that the voltage inputted to
the third power supply unit reaches a predetermined
threshold, and
wherein the control unit puts the main switching unit
in a conducting state and simultaneously puts the auxiliary
switching unit in a non-conducting state if the current
detection unit detects that the current flowing into the
auxiliary switching unit reaches a predetermined threshold.
9. The load control device of claim 8, further comprising
a zero-cross detection unit which detects a zero-cross point
of a load current,
wherein after putting the main switching unit in a
conducting state, the control unit puts the main switching
unit in a non-conducting state after a predetermined period,
that is shorter than half cycle of the load current, after
the zero-cross detection unit detects the zero-cross point
of the load current.
10. The load control device of claim 9, wherein after
putting the main switching unit in a non-conducting state,
the control unit puts the auxiliary switching unit in a
conducting state for a predetermined period.

11. The load control device of claim 10, wherein the
control unit first puts the main switching unit in a
conducting state if the current detection unit detects that
the current flowing in the auxiliary switching unit reaches
a predetermined threshold, and then puts the auxiliary
switching unit in a conducting state when the main switching
unit turns into a non-conducting state.
12. The load control device of any one of claims 8 to 11,
wherein the current detection unit includes an integrating
circuit.
13. The load control device of any one of claims 8 to 12,
wherein when power is supplied to the load, if the voltage
detection unit fails to detect that the voltage inputted to
the third power supply unit reaches a predetermined
threshold within a predetermined standby time limit, the
control unit puts the auxiliary switching unit in a
conducting state after the standby time limit is elapsed.
14. A two-wire load control device connected in series
between an AC power source and a load, comprising:
a main switching unit which includes a switch element
having a transistor structure, and controls a supply of
power to the load;
an auxiliary switching unit which includes a switch

element having a thyristor structure, and controls the
supply of power to the load when the main switching unit is
in a non-conducting state;
a control unit which controls opening/closing of the
main switching unit and the auxiliary switching unit;
a first power supply unit, to which power is supplied
from both terminals of the main switching unit through a
rectifying unit, for supplying a stable voltage to the
control unit;
a second power supply unit, to which power is supplied
from both terminals of the main switching unit through the
rectifying unit, for supplying power to the first power
supply unit when no power is supplied to the load;
a third power supply unit for supplying power to the
first power supply unit when power is supplied to the load
in a closed state of the main switching unit or the
auxiliary switching unit;
a voltage detection unit which detects a voltage
inputted to the third power supply unit; and
a manipulation unit which is manipulated by a user to
adjust a current flowing in the load,
wherein the control unit sets a main switching unit
conducting time which is counted in order to put the main
switching unit in a conducting state every half cycle of the
AC power source in response to a manipulation inputted to
the manipulation unit, and

wherein the control unit puts the main switching unit
in a conducting state only while a predetermined period,
which is counted from when the voltage detection unit
detects that the voltage inputted to the third power supply
unit reaches a predetermined threshold, overlaps with the
main switching unit conducting time.
15. The load control device of claim 14, further
comprising a zero-cross detection unit which detects a zero-
cross point of a load current,
wherein after the zero-cross detection unit detects
the zero-cross point, the control unit counts a main
switching unit non-conducting time for putting the main
switching unit in a non-conducting state in response to the
manipulation inputted to the manipulation unit, and then
counts the main switching unit conducting time.
16. The load control device of any one of claims 6, 7, 14
and 15, wherein the control unit puts the auxiliary
switching unit in a conducting state only for a
predetermined period when a state of the main switching unit
is a non-conducting state.
17. The load control device of claim 16, further
comprising a current detection unit which detects a current
flowing into the auxiliary switching unit,

wherein the control unit first puts the main switching
unit in a conducting state if the current flowing in the
auxiliary switching unit is equal to or larger than a
predetermined threshold, and then puts the auxiliary
switching unit in a conducting state when the main switching
unit turns into a non-conducting state.
18. The load control device of any one of claims 6 to 17,
further comprising a drive circuit for driving the main
switching unit,
wherein the main switching unit includes a main switch
element which is connected in series to the AC power source
and the load,
wherein the main switch element has a lateral dual
gate transistor structure having two gates, to each of which
a control voltage is applied, with respect to connection
points respectively connected to the AC power source and the
load, and
wherein the lateral dual gate transistor structure has
a withstand voltage maintaining region at one location.
19. The load control device of claim 18, wherein the drive
circuit supplies, on the basis of a drive signal transmitted
from the control unit, power electrically isolated from the
control unit to each of the gates of the main switch element
by using as a reference a potential of each of the

connection points respectively connected to the AC power
source and the load, and drives the main switch element.
20. The load control device of claim 19, wherein the drive
circuit includes two optically coupled semiconductor switch
elements corresponding to the dual gates of the main switch
element and have light emitting parts and light receiving
parts;
wherein each of the light emitting parts is connected
to the control unit and receives a drive signal inputted
from the control unit, and each of the light receiving parts
performs photoelectric conversion when light emitted from
each of the light emitting parts is incident thereon; and
wherein each of the light emitting parts is connected
such that power is generated in each of the light receiving
parts to apply a positive potential to each of the gates of
the main switch element by using as a reference each of the
connection points as the reference respectively connected to
the AC power source and the load.
21. The load control device of claim 19, wherein the drive
circuit includes a transformer having a primary coil
connected to the control unit, and two secondary coils
corresponding to the dual gates of the main switch element
and connected to the gates of the main switch element
through rectifier circuits, and

wherein power, obtained by rectifying an electromotive
force generated in each of the secondary coils when
alternating current flows in the primary coil on the basis
of the drive signal transmitted from the control unit,
applies a positive potential to each of the gates of the
main switch element by using as a reference each of the
connection points respectively connected to the AC power
source and the load.
22. The load control device of claim 18, wherein the drive
circuit includes two diodes corresponding to the dual gates
of the main switch element and connected to the first power
supply unit, capacitors having one ends connected to
respective power lines and the other ends connected to the
diodes, and drive switch elements connected between the
gates of the main switch element of the main switching unit
and connection points between the diodes and the capacitors,
and
wherein the drive circuit supplies driving power to
the main switching unit by putting the drive switch elements
in a conducting state based on a signal transmitted from the
control unit.
23. The load control device of claim 22, wherein the drive
switch elements of the drive circuit are optically coupled
semiconductor switch elements having light emitting parts

each of which emits light by a drive signal transmitted from
the control unit and light receiving parts each of which
receives the light emitted from the respective light
emitting parts to be in a conducting state, and
wherein driving power is supplied to the main
switching unit using power of the first power supply unit by
putting the light emitting parts in a conducting state.
24. The load control device of claim 20 or 23, wherein the
light emitting parts of the two optically coupled
semiconductor switch elements of the drive circuit are
connected in series to each other.
25. The load control device of any one of claims 22 to 24,
wherein the drive circuit includes capacitors connected
between power lines each of which is used as a reference of
each of the gates and connection points between the gates of
the main switch element and the drive switch elements.
26. The load control device of any one of claims 18 and 22
to 25, further comprising synchronous switching elements
connected between a point connected to an AC line of the
rectifying unit and a minus output point of the rectifying
unit, wherein an operation of closing the synchronous
switching elements is performed in synchronization with an
operation of closing the main switching unit.

27. The load control device of claim 2 6, wherein the drive
switch elements have a thyristor or triac structure, and are
driven based on a signal isolated from any of the power
supply units of the load control device.

ABSTRACT

A load control device includes: a main switching unit
which has a main switch element connected in series to an AC
power source and a load and controls the supply of power to
the load; a manipulation switch that outputs a start-up
signal for starting at least the load; a control unit which
controls the opening and closing of the main switching unit;
a first power source unit supplying a stable voltage to the
control unit; and a second and a third power source unit
each supplying power to the first power source unit. The
load control device is characterized in that upon receiving
the start-up signal, the control unit outputs an initial
drive signal, for closing the main switch element, to the
main switching unit before a power source supplying power to
the first power source unit is switched from the second to
the third power source unit.