Field of the Invention
The present invention relates to a load control device
applicable to a load, such as an illumination device into
which an inrush current flows at a time of a start-up of the
load.
Background of the Invention
As described in Patent Document 1, for example, to
carry out an ON/OFF control of a load, such as an
illumination device or the like, a load control device
(electronic relay) uses a semiconductor switch device, such
as a TRIAC or the like as a switching unit. In such a load
control device, the switching unit is connected in series
between a commercial AC power source and the load. For
example, when an operation handle of a switch is manipulated
by a user, a control unit outputs a gate driving signal to
put a switch device in an electrical conducting state.
Accordingly, power is supplied to a load from the commercial
AC power source to thereby start up the load. If a TRIAC
serves as the switch device, the TRIAC turns into an
electrical non-conducting state by a zero-cross voltage of
the commercial AC power source since the TRIAC is a self-
extinguishing element. Therefore, the gate driving signal
-Ifc

is outputted from the control unit at every half cycle of
the commercial AC power source until the operation handle is
manipulated again.
Meanwhile, when the operation handle is manipulated by
the user, namely, at the startup of the load, a high current
referred to as inrush current flows temporarily in the load.
For example, if it is assumed that the load is an
illumination device using an incandescent lamp, a resistance
of a filament in a room temperature is much lower than a
steady state resistance of the filament, so that there flows
an inrush current, which is equal to or higher than ten
times the steady state current of the illumination device.
The transistor as represented by, e.g., MOSFET, is
characterized in that a current which can flow between the
source and the drain is limited depending on the gate
voltage. For this reason, if a low voltage of the gate
driving signal is inputted to the gate electrode of the
switch device and thus only a current lower than the inrush
current can flow, the illumination device is not immediately
put into the steady state even when the operation handle is
manipulated. Instead, the brightness is gradually increased
as temperature, of the filament is increased. Therefore, in
order to immediately put the illumination device into the
steady state after the operation handle is manipulated, a
higher voltage of the gate driving signal is preferably
inputted to the gate electrode of the switch device to

smoothly flow the inrush current at start-up of the load.
However, if the voltage of the gate driving signal becomes
higher, power consumed by a gate driving unit increases.
In the load control device described in Patent
Document 1, the gate driving unit generates the gate driving
signal at every half cycle of the commercial AC power source
in response to the control signal outputted from the control
unit. Since, the gate driving unit and the control unit
shares a power source either to generate the gate driving
signal or to ensure a driving power for the control unit, it
is practically impossible to vary the voltage of the gate
driving signal in response to the current flowing through
the load.
Further, the load control device described in Patent
Document 1 is a so-called two-wire electronic switch
connected in series between the commercial AC power source
and the load, and the current flows into the load regularly
to ensure an internal power thereof. Accordingly, the
current flows into the load even while the illumination
device is turned off and thus, such a current for ensuring
the internal power needs to be set as small as possible such
that the load is not erroneously turned on. Consequently,
it is required to reduce the power consumed by the control
unit and the gate driving unit as low as possible.
[Patent Document 1] Japanese Patent Application
Publication No. 2007-174576

Summary of the Invention
The present invention provides a load control device
capable of flowing an inrush current at start-up of a load
fully while suppressing power consumed by a control unit and
a gate driving unit.
In accordance with an embodiment of the present
invention, there is provided a load control device
including: a switching unit, which is connected to a power
source and a load in series, including a switch device
having a transistor structure; a control unit configured to
control start-up and stop of the load; a gate driving unit,
which is electrically insulated from the control unit and is
configured to output a gate driving signal to a gate
electrode of the switch device; and a power source unit
configured to ensure power to operate the control unit and
the gate driving unit. Further, the control unit controls
the gate driving unit to supply a higher driving power to
the gate electrode of the switch device for a period of time
starting at the start-up of the load than in a steady state.
Further, the gate driving unit may be electrically
insulated from the control unit by having a photo-coupling
configuration in which a light emitting part and a light
receiving part are provided, and the control unit may
control a current, which flows to turn on a light emitting

element for a period of time, to be higher at the start-up
of the load than in the steady state.
Further, the gate driving unit may be electrically
insulated from the control unit by having a magnetic-
coupling configuration in which a transformer is provided,
and the control unit may control an ON-duty of a driving
signal for switching on and off a primary coil of the
transformer for a period of time to be greater at the start-
up of the load than in the steady state.
Further, the switch device may have a configuration in
which two vertical transistor elements are connected in
series with their parasitic diodes directed in opposite
directions.
Further, the switch device may have a configuration in
which two lateral transistor elements are connected in
series such that the two lateral transistor elements are
driven by the gate driving signal obtained by using a
voltage at a connection node therebetween as a reference.
Further, the switch device may include a bidirectional
switch element having a lateral transistor structure which
uses a GaN/AlGaN structure and has two gate electrodes.
• Further, the gate driving unit may further include a
charge extraction unit configured to extract residual
charges accumulated in the gate electrode of the switch
device; a driving power source unit configured to drive the
charge extraction unit; and a delay circuit which allows the

charge extraction unit not to be operated when the primary
coil of the transformer is switched on and off.
Further, the load control device may be a two-wire
load control device connected in series between the power
source and the load, and the power source may be a
commercial AC power source. The two-wire load control
device may further include the power source unit configured
to ensure power to operate the control unit and the gate
driving unit, and the power source unit is connected in
parallel to both terminals of the switching unit and
operates at every half cycle of the commercial AC power
source to ensure an internal power even while the load is
not operated.
Further, the load control device described above may
further include the power source unit configured to ensure
power to operate the control unit and the gate driving unit,
and a voltage monitoring unit configured to monitor an
output voltage of the power source unit. Further, the
control unit may control an ON-duty of the driving signal at
the start-up of the load, which is greater than in the
steady state, to be equal to an ON-duty in the steady state
based on the monitored output voltage of the power source
unit.
Further, with respect to the gate electrode of the
switch device, the gate driving unit may be configured to
perform a constant current drive for a period of time

starting at the start-up of the load and perform a constant
voltage drive in the steady state.
Further, the switch device may have a configuration in
which the transistor element and a switch element having
contacts are connected to each other in series.
Further, the switch device may have a configuration in
which the transistor element and a switch element having
contacts are connected to each other in parallel.
A switch device having a transistor structure is
characterized in that the more power is supplied to the gate
electrode, the more current flows through the switch device.
In accordance with the present invention, the gate driving
unit supplies a higher driving power to the gate electrode
of the switch device for a predetermined period of time
starting at the start-up of the load than in a steady state.
Therefore, a current amount that can flow through the switch
device is increased, thereby making an inrush current flow
fully at the start-up of the load. Further, after the
predetermined period of time has elapsed, a driving power
corresponding to a current flowing through the load in the
steady state is supplied to the gate electrode of the switch
device, so that it becomes possible to suppress power
consumed by the control unit and the gate driving unit.
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 shows a configuration of a load control device
in accordance with an embodiment of the present invention;
FIG. 2 shows a block diagram of a two-wire load
control device;
FIG. 3 shows a block diagram of a three-wire load
control device;
FIG. 4 shows a change in a gate driving power in the
load control device;
FIG. 5 shows a configuration example in which a
vertical MOSFET is used for a switch device;
FIG. 6 shows a configuration example in which a switch
element having a lateral transistor structure using a
GaN/AlGaN structure is used for the switch device;
FIG. 7 is a plan view showing a configuration of the
switch element having the lateral transistor structure using
the GaN/AlGaN structure;
FIG. 8 is a cross-sectional view taken along line
VIII-VII shown in FIG. 7;
FIG. 9 shows a configuration example in which a
bidirectional switch element having a lateral transistor
structure using a GaN/AlGaN structure is used for the switch
device;

FIG. 10 is a plan view showing a configuration of the
bidirectional switch element having the lateral transistor
structure using the GaN/AlGaN structure;
FIG. 11 is a cross-sectional view taken along line XI-
XI shown in FIG. 10;
FIG. 12 shows a configuration example in which a
MOSFET is used for the switch device of a switching unit,
and the gate driving unit has a photo-coupling
configuration;
FIG. 13 shows a configuration example in which the
bidirectional switch element is used for the switch device,
and the gate driving unit has a magnetic coupling
configuration;
FIG. 14 shows waveforms of a driving signal and the
like in the configuration example shown in FIG. 13;
FIG. 15 shows a configuration example in which, with
respect to the gate electrode of the switch device, a
constant current drive is carried out for a predetermined
period of time from the start-up of the load, while a
constant voltage drive is carried out during the steady
state;
FIG. 16 shows a configuration example in which the
gate driving unit shown in FIG. 15 further includes charge
extraction units each for extracting residual charges;
FIG. 17 shows a modification of the configuration
shown in FIG. 2 in which a voltage monitoring unit is

further included to monitor an output voltage of the power
source unit;
FIG. 18 shows waveforms of a driving signal and the
like in the configuration example shown in FIG. 17;
FIG. 19 shows a modification of the configuration
example shown in FIG. 9;
FIG. 2 0 shows another modification of the
configuration example shown in FIG. 9; and
FIG. 21 shows a usage example of the load control
device.
Detailed Description of the Embodiments
Hereinafter, an embodiment of the present invention
will be described in detail 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
functions and configurations, and a redundant description
thereof will be omitted.
A load control device (e.g., an electronic relay) 1 in
accordance with an embodiment of the present invention will
be described with reference to FIG. 1. The load control
device 1 is an electronic switch in which a switch device
having a transistor structure serves as a switching unit,
and is used to control start-up (turn on) and stop (turn

off) of a load such as an illumination device. FIG. 1 shows
a state where the load control device 1 is attached to a
building wall. A main body 2 of the load control device 1
is attached to a frame 3, and an operation handle 4 is
installed to the main body 2.
On a front surface 21 of the main body 2 of the load
control device 1, there are provided a push-on/push-off
switch 22 and a hinge 23, which is connected to the
operation handle 4. On. a rear surface 41 of the operation
handle 4, there are formed a protrusion 42 to be in contact
with the push-on/push-off switch 22 and a hinge 43 to be
connected to the hinge 23. The operation handle 4 is
generally biased by a spring of the push-on/push-off switch
22 in one direction to be protruded outwardly from the
building wall. Every time the user manipulates the
operation handle 4, the push-on/push-off switch 22 is
cyclically turned on and off.
At a rear surface 24 of the main body 2 of the load
control device 1, there are formed wire inlets 25 into which
core wires 51 of wiring cables 5 made of, e.g., a VVF cable
(Vinyl insulated Vinyl .sheathed Flat-type cable: 600V) are
inserted. Further, although a two-wire load control device
1 is described in FIG. 1 as an example of the load control
device, a three-wire load control device may be used instead
A circuit board 2 6 is provided in the main body 2 of the
load control device 1, and a switching unit, a control unit,

a gate driving unit, a power source unit and the like are
mounted on the circuit board 26.
FIG. 2 shows a block diagram of the load control
device 1 having a two-wire configuration. FIG. 3 shows a
block diagram of the load control device 1 having a three-
wire configuration. The load control device 1 includes a
switching unit 11 connected to a commercial AC power source
6 and a load 7 in series; a control unit 12 which controls
start-up and stop of the load 7; a gate driving unit 13
electrically insulated from the control unit 12; and a power
source unit 14 which ensures power to operate the control
unit 12 and the gate driving unit 13. The power source unit
14 is connected in parallel to both terminals of the
switching unit 11 and operates at every half cycle of the
commercial AC power source 6 to ensure an internal power
even while the load 7 is not operated. The switching unit
11 includes a switch device having a transistor structure.
The gate driving unit 13 generates a gate driving signal,
which is inputted to a gate electrode of the switch device,
in response to a control signal outputted from the control
unit 12.
In case of the two-wire load control device 1 shown in
FIG. 2, the power source unit 14 includes a rectifying unit
14a connected to the commercial AC power source 6 and the
load 7 in series; an OFF-power source unit 14b for ensuring
power when no power is supplied to the load 7; and an 0N-

power source 14c for ensuring power when power is supplied
to the load 7. Since the specific configurations of the
OFF-power source unit 14b and the ON-power source unit 14c
are described in detail in Patent Document 1, the detailed
description thereof will be omitted. Alternatively, in case
of the three-wire load control device 1 shown in FIG. 3, the
power source unit 14 includes a rectifying unit and a
voltage conversion unit (not shown), and power is regularly
supplied thereto from the commercial AC power source 6.
The control unit 12, which includes a CPU, detects
whether the push-on/push-off switch 22 is turned on or off,
or whether a signal is outputted from the push-on/push-off
switch. The push-on/push-off switch 22 may be configured to
maintain "ON" or "OFF" state when switched, or may be
configured to output a pulse signal whenever the operation
handle 4 is manipulated.
The switch device included in the switching unit 11 is
not particularly limited; the switch device may include a
bidirectional switch element such as a TRIAC or the like, or
a combination of two one directional switch elements (e.g.,
two thyristors, two MOSFET, or the like) . The MOSFET is
characterized in that a current that can flow through a
drain-source channel increases as a voltage of the gate
driving signal increases. FIG. 4 shows the change in a gate
driving power in the load control device 1. In this
embodiment, a driving power higher than that in a steady

state (normal stable operation) of the load 7 is supplied
for a predetermined period of time to the gate electrode of
the switch device at the start-up of the load 7, thereby
increasing a current that can flow through the switch device
Accordingly, it becomes possible to have an inrush current
to flow fully at the start-up of the load 7. In addition, a
driving power, which corresponds to a current flowing
through the load 7 in the steady state, is supplied to the
gate electrode of the switch device after the predetermined
period of time has elapsed, thereby reducing power consumed
by the control unit 12 and the gate driving unit 13.
FIG. 5 shows a configuration example in which two
vertical MOSFETs Ql and Q2 are used for the switch device
having the transistor structure, wherein they are connected
in series with their parasitic directed in the opposite
directions. In this case, the gate driving unit 13 controls
the voltage signal, i.e., the voltage of the gate driving
signal, by using a voltage at a node between the two
vertical MOSFETs Ql and Q2 as a reference voltage, to
thereby control a switching operation of the switching unit
11.
FIG. 6 shows a configuration example in which two
switch elements 101 connected in series, each having a
lateral transistor structure using a GaN/AlGaN structure,
are used for the switch device having the transistor
structure. In the similar manner, the gate driving unit 13

controls the voltage signal, i.e., the voltage of the gate
driving signal, by using a voltage at a node between the two
switch elements 101 as a reference voltage to thereby
control a switching operation of the switching unit 11.
Each of the switch elements 101 is a lateral single gate
transistor element. FIG. 7 is a plan view showing a
configuration of the switch element 101, and FIG. 8 is a
cross-sectional view taken along line VIII-VIII shown in FIG
7.
As shown in FIG. 8, a substrate 120 of the switch
element 101 includes a base layer 101a, and a GaN layer 101b
and an AlGaN layer 101c which are stacked on the base layer
101a. In this switch element 101, a two-dimensional
electron gas layer generated at an AlGaN/GaN heterogeneous
interface is used as a channel layer. As shown in FIG. 7,
on a surface 120d of the substrate 120, there are formed a
first electrode D1 and a second electrode D2, which are
connected with the commercial AC power source 6 and the load
7, and an intermediate potential portion S having an
intermediate potential between the potentials of the first
electrode Dl and the potential of the second electrode D2.
Further, a gate electrode G is formed on the intermediate
potential portion S. For example, a Schottky electrode is
used as the gate electrode G.
The first electrode D1 has a comb shape having
electrode portions 111, 112, 113 ••• arranged in parallel to

one another, and the second electrode D2 has a comb shape
having electrode portions 121, 122, 123 ••• arranged in
parallel to one another. The comb-shaped electrode portions
of the first electrode Dl and the comb-shaped electrode
portions of the second electrode D2 are arranged to face
oppositely to each other. The intermediate potential
portion S and the gate electrode G are respectively disposed
between the comb-shaped electrode portions 111, 112, 113
and 121, 122, 123 •••, and they have a shape similar to the
planar shape of the space defined between the electrode
portions.
As shown in FIG. 7, the electrode portion 111 of the
first electrode Dl and the electrode portion 112 of the
second electrode D2 are arranged such that their center
lines in the width direction are aligned with each other.
In addition, the corresponding portion of the intermediate
potential portion S and the corresponding portion of the
gate electrode G are positioned in parallel to the electrode
portion 111 of the first electrode Dl and the electrode
portion 121 of the second electrode D2. Distances in the
width direction from the electrode portion 111 of the first
electrode- D1 and the electrode portion 112 of the second
electrode D2 to the corresponding portions of the
intermediate potential portion S and the gate electrode G
are set such that a predetermined withstand voltage can be
maintained. Distances in the longitudinal direction of the

electrode portion 111 of the first electrode Dl and the
electrode portion 112 of the second electrode D2, i.e.,
perpendicular to the width direction are also set in the
same manner. In addition, such relationships are applied to
those of the other electrode portions 112 and 122, 113 and
123, and so on. That is, the intermediate potential portion
S and the gate electrode G are disposed at positions at
which a predetermined withstand voltage can be maintained
with respect to the first electrode D1 and the second
electrode D2.
The intermediate potential portion S having the
intermediate potential between the potential of the first
electrode Dl and the potential of the second electrode D2,
and the gate electrode G connected to the intermediate
potential portion S to control the intermediate potential
portion S are disposed at positions at which a predetermined
withstand voltage can be maintained with respect to the
first electrode Dl and the second electrode D2. Therefore,
assuming that the first electrode Dl is in a high potential
side and the second electrode D2 is in a low potential side,
when the switch element 101 is turned off (that is, a signal
having a zero voltage is applied to the gate electrode G) ,
the current is completely interrupted between at least the
first electrode D1, and the gate electrode G and the
intermediate potential portion S. In other words, the
current is blocked right under the gate electrode G.

On the other hand, when the switch element 101 is
turned on (that is, a signal having a voltage equal to or
higher than a predetermined threshold is applied to the gate
electrode G) , a current flows through a path of the first
electrode D1, the intermediate potential portion S, and the
second electrode D2 as indicated by the arrow in the FIG 7,
or vice versa.
Since the intermediate potential portion S is disposed
at the position at which a predetermined withstand voltage
can be maintained with respect to the first electrode Dl and
the second electrode D2, it becomes possible to securely
turn on/off the switch element 101 even when the threshold
voltage of the signal applied to the gate electrode G is
lowered to the required minimum level. As a result, a low
on-resistance of the switch device can be achieved. Further,
the switching unit 11 includes the switch element 101
configured in such a way that the reference (GND) of the
control signal is set to have the same potential as the
intermediate potential portion S. Accordingly, it becomes
possible to directly control the commercial AC power source
6 having a high voltage by the control unit 12 that is
driven by a control signal of several voltages. Further, in
the lateral transistor element using, as a channel layer, a
two-dimensional electron gas layer generated at a
heterogeneous interface, there is a trade-off relationship
between increasing the potential of a threshold voltage for

putting the element in a non-conducting state and the on-
resistance in a conducting state. Therefore, 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 1.
FIG. 9 shows a configuration example in which one
bidirectional switch element 300 having a lateral transistor
structure using a GaN/AlGaN structure is used for the switch
device having the transistor structure. The bidirectional
switch element 300 has two gate electrodes and is connected
to the commercial AC power source 6 and the load 7 in series
FIG. 10 is a plan view showing a configuration of the
bidirectional switch element 300, and FIG. 11 is a cross-
sectional view taken along line XI-XI shown in FIG. 10.
As shown in FIG. 11, the bidirectional switch element
300 includes a first electrode D1 and a second electrode D2
formed on a substrate surface, and a first gate electrode G1
and a second gate electrode G2 at least a part of each of
which is formed on the substrate surface, wherein separate
control signals are inputted to the first and the second
gate electrode G1 and G2. Further, the first gate electrode
G1 and the second gate electrode G2 are disposed in such a
way that a predetermined withstand voltage can be maintained
Since the bidirectional switch element 300 is configured to
have a single portion for maintaining a withstand voltage
between the first gate electrode G1 and the second gate

electrode G2, it is possible to implement a bidirectional
switch element with a small loss. Further, the
bidirectional switch element 300 with such a configuration
needs to be controlled based on the voltages of the drain
electrodes D1 and D2, and therefore it is necessary to input
separate drive signals to the respective gate electrodes G1
and G2 (thus, referred to as a dual gate transistor
structure). The bidirectional switch element 300 is
substantially equivalent to the circuit shown in FIG. 5 in
which two vertical MOSFETs are connected in series while
their parasitic diodes are directed in the opposite
directions.
FIG. 12 shows a configuration example in which, for
example, the MOSFETs shown in FIG. 5 are used for the switch
device of the switching unit 11, and the gate driving unit
13 has a photo-coupling configuration. More specifically,
optical MOSFETs are used for the switch device, and the
switching unit 11 and the gate driving unit 13 are
integrated into a single unit. The control unit 12 controls
a current, which flows to turn on a light emitting element
for a predetermined period of time, to be higher at rhe
start-up of the load 7 than the current that flows in a
steady state. Further, in a case where the switch element
having the lateral transistor structure using the GaN/AlGaN
structure shown in FIG. 6 or FIG. 9 is used for the switch
device, a photo-coupler may be connected to the gate

electrode of the switch device. Since the gate driving unit
13 has the photo-coupling configuration, it is possible to
successfully control power generated at the secondary side
(gate electrode side) by controlling the primary side (light
emitting element side).
FIG. 13 shows a configuration example in which the
bidirectional switch element shown in FIG. 9 is used for the
switch device, and the gate driving unit 13 has a magnetic
coupling configuration. In the configuration example of FIG.
13, a primary coil of a transformer 131 is electrically
insulated from two secondary coils of the transformer 131.
Rectifying circuits such as diode bridges and stabilization
circuits for stabilizing rectified voltages of the
rectifying circuits are connected to the secondary coils of
the transformer 131, respectively. FIG. 14 shows waveforms
of a driving signal and the like in the case of using the
gate driving unit 13 having the magnetic coupling
configuration. Under the PWM control of the control unit 12,
ON-duty of the driving signal, by which the primary coil of
the transformer 131 is switched on and off for a
predetermined period of time, is set to be greater at the
start-up of the load 7 than in the steady state. Since the
gate driving unit 13 has the magnetic-coupling configuration,
it is possible to successfully control powers generated at
the secondary coils by controlling the switching duty of the
primary coil of the transformer 131.

FIG. 15 shows a configuration example in which, with
respect to the gate electrode of the switch device, a
constant current drive is carried out for a predetermined
period of time from the start-up of the load 7, and a
constant voltage drive is carried out during the steady
state. As described above, the control unit 12 controls 0N-
duty of the driving signal, by which the primary coil of the
transformer 131 is switched on and off for a predetermined
period of time, to be greater at the start-up of the load 7
than in the steady state. In other words, currents, which
flow through the secondary coils of the transformer 131 for
the predetermined period of time after the start-up of the
load 7, become higher than those that flow in the steady
state, and further a voltage drop occurs across each
resistor R13. When the voltage drop across the resistor R13
becomes greater than a forward voltage drop in a diode D13,
a current will flow through the diode D13. Accordingly, the
current flowing through the gate electrode of the switch
device becomes constant (constant current drive). When the
ON-duty of the driving signal becomes smaller during the
steady state, the current merely flows through the resistor
R13 and a constant voltage is applied to the gate electrode
of the switch device (constant voltage drive). With such
configuration, only necessary amount of the current flows to
the gate electrode of the switch device, thereby reducing
power consumed by the gate drive of the switch device.

FIG. 16 shows another configuration example in which
the gate driving unit 13 shown in FIG. 15 further includes
charge extraction units 132 each for extracting residual
charges accumulated in a capacitor included in the gate
driving unit 13, a parasitic capacitance of the switch
device, and the like; and driving power source units 133
each for supplying a driving power to the corresponding
charge extraction unit 132. As is generally known, the
switch device having the transistor structure has a
parasitic diode, and electric charges are accumulated in the
parasitic diode during the gate drive. The gate driving
unit 13 further includes capacitors C13 as a part of the
components in its configuration.
Due to the accumulated charges in these capacitances,
even if the voltage level of the gate driving signal becomes
low, the gate voltage of the switch device is not
immediately lowered, and the switch device keeps its
conducting state. In this configuration example, each
charge extraction unit 132 is operated at the zero cross
point of the commercial AC power source, and the residual
charges are rapidly extracted out from the gate electrode of
the switch device, thereby putting the switch device in a
non-conducting state rapidly.
Each of the charge extraction units 132 includes
normally-on' type transistor T13. The transistor T13 is
turned off and the charge extraction unit 132 is not

operated when the charges are accumulated in the capacitor
C13. The transistor T13 is turned on and the charge
extraction unit 132 is operated to rapidly extract the
residual charges accumulated in the capacitor C13 and the
parasitic capacitance of the switch device when the voltage
of the commercial AC power source 6 becomes zero (zero cross
point) .
Further, each of the driving power source units 133
has a time constant (delay circuit) which allows its power
not to be zero during a half cycle of the commercial AC
power source 6, and the charge extraction unit 132 is not
operated when the primary coil of the transformer 131 is
switched on and off.
FIG. 17 shows a modification of the configuration
shown in FIG. 2 in which a voltage monitoring unit 15 is
further included to monitor an output voltage of the power
source unit 14. In a case where the load control device 1
is the two-wire load control device as shown in FIG. 2,
charges accumulated in a buffer capacitor (not shown) of the
power source unit 14a are the only power source used for
driving the control unit 12 or the gate driving unit 13. In
the load control device 1, the ON-duty of the driving signal
at the start-up of the load 7 is set to be greater than in
the steady state. As a result, the power consumption is
increased by that amount compared to that in the steady
state, and further the charged power in the buffer capacitor

is rapidly consumed. Therefore, the voltage monitoring unit
15 is further provided to monitor the output voltage of the
power source unit 14, so that, based on the monitored output
voltage of the power source unit 14, the control unit 12
controls the ON-duty of the driving signal at the start-up
of the load, which is greater than in the steady state, to
be equal to an ON-duty in the steady state.
As shown in FIG. 18, the output voltage of the power
source unit 14 is gradually lowered by the standby power of
the control unit 12 and the like, and is sharply lowered
when generating the gate driving signal. Therefore, it is
preferable to set the threshold to the output voltage of the
power source unit 14 such that the ON-duty of the driving
signal is changed to the value of that in the steady state
when the output voltage of the power source unit 14 is equal
to or less than the threshold. The power consumption of the
buffer capacitor may thereby be suppressed. Further, the
voltage monitoring unit 15 is applicable to the third-wire
load control device and is effective in reducing the power
consumed when generating the gate driving signal.
The present invention is not limited to the embodiment
described above, and various changes and modifications may
be made without departing from the scope of the invention.
For example, a power source for supplying power to the load
7 is not limited to the commercial AC power source 6, and a
DC power source may be used. A photovoltaic device having

solar panels and the like may be used as an example of the
DC power source, and the load 7 that is connected to the DC
power source may be, e.g., a battery for use in an electric
vehicle and the like.
FIG. 21 shows a usage example of the load control
device 1 in accordance with the present invention. The load
control device 1 is connected in series to a power
conversion circuit 31 provided for supplying power to a DC
power source 30 and the load 7. Here, the load control
device 1 serves as a relay for controlling a DC power to be
supplied to the power conversion circuit 31. Accordingly,
the load control device 1 can be used as a general relay to
control power to be supplied to the power conversion circuit
31 or power to be directly supplied to the load 7.
Further, the power source unit 14 obtains power
regularly from the commercial AC power source 6 as shown in
FIGs. 2 and 3, but it is not limited thereto. The power
source unit 13 may be configured to obtain power from other
power systems.
FIG. 19 shows a modification of the configuration
example shown in FIG. 9 in which the bidirectional switch
element having the lateral transistor structure using the
GaN/AlGaN structure is used for the switch device. In this
modification, the switch device having the transistor
structure is connected in series to a mechanical relay
(switch element) 400 haying contacts. The mechanical relay

400 performs its switching operation based on the control
signal outputted from the control unit 12. In this
modification, when closing the bidirectional switch element
300, the switch element 400 is closed first and then the
bidirectional switch element 300 is closed. When opening
the bidirectional switch element 300, the bidirectional
switch element 300 is opened first and then the switch
element 400 is opened. With such configuration, by properly
controlling both of the bidirectional switch element 300
having the transistor structure and the switch element
having contacts, which are connected in series to each other,
it becomes possible to suppress an arc generation during the
switching operation. Further, it is possible to improve an
isolation property of a power supply interruption unit 3
when interrupting the supply of power.
Further, FIG. 20 shows another modification of the
configuration example shown in FIG. 9 in which the
bidirectional switch element having the lateral transistor
structure using the GaN/AlGaN structure is used for the
switch device. In this modification, the switch device
having the transistor structure is connected in parallel to
the mechanical relay (switch element) 400 having contacts.
The mechanical relay 400 performs its switching operation
based on the control signal outputted from the control unit
12. In this modification, when closing the bidirectional
switch element 300, the bidirectional switch element 300 is

closed first and then the switch element 400 is closed.
When opening the bidirectional switch element 300, the
switch element 400 is opened first and then the
bidirectional switch element 300 is opened. With such
configuration, by properly controlling both of the
bidirectional switch element 300 having the transistor
structure and the switch element having contacts, which are
connected in parallel to each other, it becomes possible to
suppress an arc generation during the switching operation.
Further, it is possible to allow a large amount of current
to flow in the load 7.
Further, the features illustrated in the configuration
examples and the drawings of the present invention can be
combined with each other in any suitable manner. In
addition, the types of the switch device included in the
switching unit 11, the configurations of the control unit 12
and the gate driving unit 13 are not particularly limited to
those described in the embodiments of the present invention.
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 load control device comprising:
a switching unit, which is connected to a power source
and a load in series, including a switch device having a
transistor structure;
a control unit configured to control start-up and stop
of the load; and
a gate driving unit, which is electrically insulated
from the control unit and is configured to output a gate
driving signal to a gate electrode of the switch device,
wherein the control unit controls the gate driving
unit to supply a higher driving power to the gate electrode
of the switch device for a period of time starting at the
start-up of the load than in a steady state.
2. The load control device of claim 1, wherein the gate
driving unit is electrically insulated from the control unit
by having a photo-coupling configuration in which a light
emitting part and a light receiving part are provided, and
wherein the control unit controls a current, which
flows to turn on a light emitting element for a period of
time, to be higher at the start-up of the load than in the
steady state.
3. The load control device of claim 1, wherein the gate

driving unit is electrically insulated from the control unit
by having a magnetic-coupling configuration in which a
transformer is provided, and
wherein the control unit controls an ON-duty of a
driving signal for switching on and off a primary coil of
the transformer for a period of time to be greater at the
start-up of the load than in the steady state.
4. The load control device of any one of claims 1 to 3,
wherein the switch device has a configuration in which two
vertical transistor elements are connected in series with
their parasitic diodes directed in opposite directions.
5. The load control device of any one of claims 1 to 3,
wherein the switch device has a configuration in which two
lateral transistor elements are connected in series such
that the two lateral transistor elements are driven by the
gate driving signal obtained by using a voltage at a
connection node therebetween as a reference.
6. The load control device of any one of claims 1 to 3,
wherein the switch device includes a bidirectional switch
element having a lateral transistor structure which uses a
GaN/AlGaN structure and has two gate electrodes.
7. The load control device of any one of claims 3 to 6,

wherein the gate driving unit further includes a charge
extraction unit configured to extract residual charges
accumulated in the gate electrode of the switch device; a
driving power source unit configured to drive the charge
extraction unit; and a delay circuit which allows the charge
extraction unit not to be operated when the primary coil of
the transformer is switched on and off.
8. The load control device of any one of claims 1 to 7,
wherein the load control device is a two-wire load control
device connected in series between the power source and the
load, the power source being a commercial AC power source,
and the two-wire load control device further includes a
power source unit configured to ensure power to operate the
control unit and the gate driving unit, and
wherein the power source unit is connected in parallel
to both terminals of the switching unit and operates at
every half cycle of the commercial AC power source to ensure
an internal power even while the load is not operated.
9. The load control device of any one of claims 1 to 7,
further comprising: a power source unit configured to ensure
power to operate the control unit and the gate driving unit,
and a voltage monitoring unit configured to monitor an
output voltage of the power source unit,
wherein the control unit controls an ON-duty of the

driving signal at the start-up of the load, which is greater
than in the steady state, to be equal to an ON-duty in the
steady state based on the monitored output voltage of the
power source unit.
10. The load control device of any one of claims 3 to 7,
with respect to the gate electrode of the switch device, the
gate driving unit is configured to perform a constant
current drive for a period of time starting at the start-up
of the load and perform a constant voltage drive in the
steady state.
11. The load control device of any one of claims 4 to 6,
wherein the switch devi*ce has a configuration in which the
transistor element and a switch element having contacts are
connected to each other in series.
12. The load control device of any one of claims 4 to 6,
wherein the switch device has a configuration in which the
transistor element and a switch element having contacts are
connected to each other in parallel.