Field of the Invention
The present invention relates to a two-wire load
control device.
Background of the Invention
Conventionally, in order to control the ON/OFF of a
load such as a lighting apparatus, a ventilation fan or the
like, a load control device (an electronic switch), in which
contacts are replaced with a two-wire switch configured to
be mechanically closed or opened and a non-contact switch
device such as a triac is employed, has been put to
practical use (see, e.g., Japanese Patent Application
Publication No. 2008-97535). Such a load control device
generally employs a two-wire connection to reduce a wire and
is connected in series between a commercial power source (an
AC power source) and a load. In the case of the load
control device connected between the commercial power source
and the load, how to acquire its own circuit power is an
issue.
Fig. 10 shows the circuit configuration of a
conventional two-wire load control device 50 that is
connected in series between a commercial power source 2 and
a load 3. This load control device 50 includes primary and
auxiliary switching units 51 and 57 configured to control
the ON and OFF of the load 3, a control unit 53 configured
to control the conduction of the primary and auxiliary
switching units 51 and 57, and a power supply circuit
configured to supply a driving power to the control unit 53.
The power supply circuit includes a rectifying unit 52, a
first power supply unit 54 configured to stabilize supply of
a power to the control unit 53, a second power supply unit
55 configured to supply a power to the first power supply
unit 54 when the power supply to the load 3 is stopped, and
a third power supply unit 56 configured to supply a power to
the first power supply unit 54 when the power supply to the
load 3 is performed. The auxiliary switching unit 57
includes, e.g., a thyristor 57a, which functions to allow a
main circuit current to flow into the load 3 when the
capacity of the load 3 is small and also only a current that
is lower than the holding current required to maintain the
conduction of the triac (main switch device) 51a of the
primary switching unit 51 flows.
The second power supply unit 55 is a constant voltage
circuit that includes, e.g., a resistor configured to limit
a current, a Zener diode {ccnstant voltage diode) 55a
configured to clip a voltage and the like. A ripple current
which has been full-wave rectified by the rectifying unit 52
is inputted into the second power supply unit 55. Further,
only when the voltage value of the inputted ripple current
is higher than the Zener voltage of the Zener diode 55a, a
current flows therethrough. A part of the current flows
into the first power supply unit 54 to be supplied as a
power of the control unit 53 and is charged in a buffer
capacitor 54a connected to the input terminal of the first
power supply unit 54. When the voltage of the ripple
current full-wave rectified by the rectifying unit 52 is
lower than the Zener voltage, the buffer capacitor 54a
becomes a power source, and thus supplies a power to the
first power supply unit 54. Accordingly, the buffer
capacitor 54a repeats charging and discharging.
In other words, even when the load 3 is in an OFF
state, a current flows into the load 3 via the Zener diode
55a and the rectifying unit 52. In this case, the current
flowing into the load 3 needs to have a small magnitude that
prevents an erroneous operation of the load 3. Further, the
current consumption of the control unit 53 is set to be kept
small and the impedance of the second power supply unit 55
is set to be kept high. Further, the first power supply
unit 54 functions as a voltage stabilization unit.
Meanwhile, when an operating handle SW 4 that
activates the load 3 is manipulated, the control unit 53
outputs a control signal to make the switch device 56c of
the third power supply unit 56 to be conductive, whereby the
buffer capacitor 54a is charged. When the buffer capacitor
54a is charged, the current passes through the Zener diode
56a, the thyristor 57a of the auxiliary switching unit 57,
and the triac 51a of the primary switching unit 51 in
sequence. When the triac 51a becomes ON, the rectification
voltage of the rectifying unit 52 becomes almost zero, and
thus, the second power supply unit 55 becomes non-conductive
and no current flows. The same is true of the third power
supply unit 56.
While the second power supply unit 55 and the third
power supply unit 56 are non-conductive, the first power
supply unit 54 is supplied with a power from the buffer
capacitor 54a, and thus, the input voltage of the first
power supply unit 54, i.e., the terminal voltage of the
buffer capacitor 54a, is gradually decreased. Meanwhile,
when the current flowing into the triac 51a becomes 0, the
triac 51a is caused to enter an open state {a non-conductive
state) by self arc-extinguishing and a voltage is generated
in the rectifying unit 52. When the voltage increases above
the terminal voltage of the buffer capacitor 54a, the buffer
capacitor 54a starts to be charged. Since the impedance of
the second power supply unit 55 is set to be a value
sufficiently higher than that of the third power supply unit
56, the second power supply unit 55 does not contribute to
the operation of the load control device 50 while the load 3
is ON.
Once the primary switching unit 51 has become
conductive (a closed state), it continuously flows the
current. However, when the commercial current reaches a
zero-cross point, the triac 51a is self arc-extinguished,
and the primary switching unit 51 becomes non-conductive (an
open state). When the primary switching unit 51 becomes
non-conductive, an operation of acquiring the circuit power
by the load control device 50, in which the current flows
from the rectifying unit 52 through the third power supply
unit 56 to the first power supply unit 54, is performed.
That is, in every half period of AC, the operation of
acquiring the circuit power by the load control device 50,
and the conduction of the auxiliary switching unit 57 and
the conduction of the primary switching unit 51 are
repeated.
However, in order to reduce the power consumption,
replacement to LED (Light-Emitting Diode) lamps has been
conducted. Since an LED device emits a light by using DC, a
power supply circuit configured to convert AC into DC is
provided in the LED lamp. However, there are power supply
circuits for some loads, such as inexpensive LED lamps,
which have no countermeasures against noise (e.g., the
parallel connection of a capacitor or the like between the
terminals of a power supply circuit) . When an LED lamp
without noise countermeasures is connected as a load to the
two-wire load control device 50, a current flows into the
load because of the acquisition of the load control device
50's own circuit power even when the load needs to be in an
OFF state. Therefore, there is a possibility of the
erroneous operation of the load (e.g., flickering of the LED
lamp). Further, in the conventional load control device 50,
a voltage is stepped down by the Zener diode 55a, and thus,
an energy corresponding to the voltage step-down is consumed
by thermal conversion. Accordingly, the conventional load
control device 50 does not contribute to the improvement of
energy efficiency.
Summary of the Invention
In view of the above, the present invention provides a
two-wire load control device capable of reducing a standby
power of a load control device (the power consumption of an
internal power source) while a load is turned off, and
preventing an erroneous operation of a load (the erroneous
light emission of an LED lamp) attributable to a leakage
current when the load, e.g., the LED lamp or the like,
without countermeasures against noise, is connected.
In accordance with an aspect of the present invention,
there is provided a two-wire load control device connected
in series between a commercial power source and a load
including: an off power supply unit configured to acquire an
internal power when the load is turned off, wherein the off
power supply unit includes a plurality of capacitors of
which series and parallel connections are switched based on
a level of input voltage. Charging and discharging of the
plurality of the capacitors are repeated and a power
obtained by discharging of the plurality of capacitors is
used as the internal power.
In accordance with another aspect of the present
invention, there is provided a two-wire load control device
connected in series between a commercial power source and a
load including: a primary switching unit configured such
that main electrodes of a main switch device are connected
in series to the commercial power source and the load, and
configured to control power supply to load; a rectifying
unit connected between the main electrodes of the main
switch device; a control unit configured to control ON and
OFF of the load in response to a signal from an outside; a
first power supply unit configured to reliably supply a
power to the control unit; a second power supply unit
configured to supply a power to the first power supply unit
when a power is supplied from both ends of the primary
switching unit via the rectifying unit and the load is
turned off; and a third power supply unit configured to
supply power to the first power supply unit when a power is
supplied from both ends of the primary switching unit via
the rectifying unit and the load is turned on.
The first power supply unit is a DC/DC converter
configured to step down an input DC current so that an
output voltage decreases below an input voltage. The second
power supply unit includes a plurality of capacitors, a
series/parallel switching circuit configured to switch
between series and parallel connections of the plurality of
capacitors, a first switch connected to an output terminal
for the first power supply unit and a first switch
controller configured to control ON (a closed state) and OFF
(an open state) of the first switch.
When a voltage inputted to the second power supply
unit is higher than a predetermined voltage, the
series/parallel switching circuit allows the plurality of
capacitors to be connected in series and charge the
plurality of capacitors, and the first switch controller
turns the first switch off (an open state) . When the
voltage inputted to the second power supply unit is equal to
or lower than the predetermined voltage, the series/parallel
switching circuit allows the plurality of capacitors to be
connected in parallel and discharge the plurality of
capacitors, and the first switch controller turns the first
switch on (a closed state), so that charging and discharging
of the plurality of capacitors are repeated, thereby
stepping down the voltage inputted from the rectifying unit
to a predetermined level and then outputting resulting
voltage.
In accordance with the above-described configuration,
in the second power supply unit (an off power supply unit)
that is the internal power source of the load control device
when the load is turned off, the peak voltage of input
voltage pulsating current is stepped down based on the
number of capacitors that are connected in series. When
voltage is stepped down by the second power supply unit (the
off power supply unit), energy loss attributable to thermal
conversion is considerably small compared to the case using
a Zener diode, and thus the standby power of a load control
device (the power consumption of an internal power source)
can be reduced. Furthermore, since a current flowing into
the load via the second power supply unit (off power supply
unit) while the load is turned off is further reduced, the
possibility of the load being erroneously operated is
reduced even when a load, such as an LED lamp without
countermeasures against noise, is connected.
The second power supply unit may further include a
voltage clamp circuit configured to clamp the voltage
inputted from the rectifying unit to a predetermined value,
thereby preventing a voltage above the predetermined voltage
from being applied to the plurality of capacitors that are
connected in series.
The series/parallel switching circuit may include a
second switch connected to terminals of the plurality of
capacitors and configured to switch between series and
parallel connections of the plurality of capacitors and a
second switch controller configured to control a connection
state of the second switch.
The plurality of capacitors may be three or more in
number, and the second switch controller varies the number
of the plurality of capacitors that are connected in series.
The second power supply unit may further include a
peak voltage detection unit configured to detect a peak
voltage of voltage from the commercial power source or the
rectifying unit, and the second switch controller varies the
number of the plurality of capacitors that are connected in
series by the second switch based on a peak voltage of the
commercial power source.
The series/parallel switching circuit preferably
includes first diodes connected in series between the
plurality of capacitors and second diodes connected such
that a current flows in an opposite direction to a direction
in which the current flows during the charging.
The plurality of capacitors may be three or more in
number, the second power supply unit may further include a
third switch connected in parallel to at least one of the
plurality of capacitors and a third switch controller
configured to control ON {a closed state) and OFF (an open
state) of the third switch, and the number of the plurality
of capacitors connected in series may be varied by
controlling the ON (closed state) and OFF (open state) of
the third switch.
The second power supply unit may further include a
peak voltage detection unit configured to detect a peak
voltage of voltage inputted from the commercial power source
or the rectifying unit, and the third switch controller
preferably varies the number of the plurality of capacitors
connected in series by the third switch based on the peak
voltage of the commercial power source.
The second power supply unit may further include a
current limiting device configured to limit an amount of
current with which the plurality of capacitors is charged
when the plurality of capacitors are connected in series.
The current limiting device may vary the amount of
current, the second power supply unit may further include an
output voltage detection unit configured to detect a voltage
outputted from the second power supply unit to the first
power supply unit and a current limiting device controller
configured to control the amount of current by the current
limiting device; and the current limiting device controller
preferably controls the amount of current by the current
limiting device based on the voltage outputted from the
second power supply unit which is detected by the output
voltage detection unit.
The second power supply unit may further include a
peak voltage detection unit configured to detect a peak
voltage of voltage inputted from the commercial power source
or the rectifying unit, and the first switch controller
preferably controls a time for which the first switch is
opened based on the peak voltage.
The first switch and the first switch controller may
be formed of semiconductor devices configured to be
conductive in response to an input of a predetermined
control signal, and a voltage outputted from the rectifying
unit may be inputted to the semiconductor devices as the
control signal.
The first switch and the first switch controller may
be formed of semiconductor devices configured to be
conductive in response to input of a predetermined control
signal, and a voltage outputted from the voltage clamp
circuit may be inputted to the semiconductor devices as the
control signal.
The first switch controller may control a time for
which the first switch is opened based on the voltage
outputted from the second power supply unit.
The voltage clamp circuit may include a plurality of
constant voltage diodes that are connected in series, and an
intermediate conjunction of the plurality of constant
voltage diodes connected in series is connected to an input
unit of the first power supply unit, so that a part of
current to flow the plurality of constant voltage diodes
connected in series is caused to flow into the first power
supply unit.
The voltage clamp circuit may include a plurality of
constant voltage diodes connected in series and a switch
device connected in parallel to at least one of the constant
operation of each component of the two-wire load control
device in accordance with the second embodiment of the
present invention;
Fig. 5 is a circuit diagram showing a configuration of
a two-wire load control device in accordance with a third
embodiment of the present invention;
Fig. 6 is a circuit diagram showing a configuration of
a two-wire load control device in accordance with a
modification of the second embodiment;
Fig. 7 is a circuit diagram showing a configuration of
a two-wire load control device in accordance with another
modification;
Fig. 8 is a circuit diagram showing a configuration of
a two-wire load control device in accordance with still
another modification;
Fig. 9 is a circuit diagram showing a configuration of
a two-wire load control device in accordance with still
another modification; and
Fig. 10 is a circuit diagram showing a circuit
configuration of a conventional two-wire load control
device.
Detailed Description of the Embodiments
Hereinafter, embodiments of the present invention will
be described in detail with reference to the accompanying
drawings which form a part hereof. The same reference
symbols are assigned to the same or like components
throughout the drawings, and redundant descriptions thereof
will be omitted.
{First Embodiment)
A two-wire load control device 1A 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 the configuration of the two-wire load
control device 1A, and Fig. 2 is a timing chart illustrating
the voltage and operation of each component. The load
control device 1A is connected in series to a commercial
power source 2 and a load 3. Like the conventional example,
the load control device 1A includes primary and auxiliary
switching units 11 and 17 configured to control the ON and
OFF of the load 3, a control unit 13 configured to control
the conduction of the primary and auxiliary switching units
11 and 17, and a power supply circuit configured to supply a
driving power to the control unit 13.
The power supply circuit includes a rectifying unit
12, a first power supply unit 14 configured to stabilize the
supply of power to the control unit 13, a second power
supply unit 15 configured to supply a power to the first
power supply unit 14 when the power supply to the load 3 is
stopped, and a third power supply unit 16 configured to
supply a power to the first power supply unit 14 when the
power supply to the load 3 is performed. Since the
auxiliary switching unit 17 includes, e.g., a thyristor 17a,
and thus supplies a current of desired magnitude to the gate
of triac (the main switch device) 11a to make the main
switch device 11a of the primary switching unit 11
conductive. The first power supply unit 14 is a DC /DC
converter that steps down an input DC current so that an
output voltage is lower than an input voltage. Since all
components except for the second power supply unit 15 are
the same as the corresponding components of the conventional
example, descriptions thereof will be omitted.
The second power supply unit 15 includes a plurality
of {e.g., three) capacitors 151a to 151c, and a plurality of
diodes 152a to 152g connected between the terminals of the
capacitors 151a to 151c. Further, a first switch (FET) 153
is connected to the output terminal 15b of the second power
supply unit 15, and the input voltage of the second power
supply unit 15 is applied to the control electrode of the
first switch 153 (gate electrode of FET). Since a full-wave
rectified ripple current (i.e., the input voltage of the
second power supply unit 15) is outputted from the
rectifying unit 12, as shown in Fig. 2, it is assumed that
the first switch 153 becomes ON (closed state) and the input
voltage of the second power supply unit 15 is 0 V.
As the input voltage of the second power supply unit
15 increases, a current flows into the first power supply
unit 14 via the diode 152a and the first switch 153. When
the input voltage of the second power supply unit 15
increases above a predetermined voltage, the first switch
153 becomes OFF (open state) and the supply of power to the
first power supply unit 14 is stopped, and thus a power is
supplied from the buffer capacitor 14a to the first power
supply unit 14.
When the first switch 153 becomes OFF (open state),
the diode 152a, the capacitor 151a, the diode 152b, the
capacitor 151b, the diode 152c, and the capacitor 151c are
connected in series to each other, and thus the current
flows to the ground via the series circuit thereof. During
the period, the capacitors 151a to 151c are respectively
charged, and the terminal voltage of each of the capacitors
151a to 151c is a voltage that is obtained by dividing the
peak voltage of input voltage by the number of capacitors
under a condition that the capacitors (parts) of the same
specifications are used. The diodes 152a, 152b and 152c
function as first diodes that connect the capacitors 151a to
151c in series.
When the input voltage of the second power supply unit
15 becomes equal to or lower than the predetermined voltage,
the first switch 153 becomes ON (closed state) again, and
the current flows into the first power supply unit 14 via
the current limiting resistor diode 152a and the first
switch 153. When the input voltage of the second power
supply unit 15 decreases below the terminal voltages of the
capacitors 151a to 151c, charges stored in the capacitors
151a to 151c start to be discharged and flow into the first
power supply unit 14 via the first switch 153. That is,
power shortage attributable to decrease in the input voltage
of the second power supply unit 15 is compensated by the
discharging of the capacitors 151a to 151c, and the circuit
configuration of the second power supply unit 15 shown in
Fig. 1 forms a so-called valley fill circuit.
Further, since the peak voltage of the input voltage
is divided by the series circuit of the plurality of
capacitors 151a to 151c and a voltage above the
predetermined voltage is not outputted by the first switch
153, the second power supply unit 15 functions as a step-
down circuit. The diodes 152a to 152g connect the
capacitors 151a to 151c in parallel and function as second
diodes that cause a current to flow in an opposite direction
to a direction in which the current flows during charging.
Further, the diodes 152a to 152g and the first switch 153
function as a series/parallel switching circuit that
switches between the series and parallel connections of the
capacitors 151a to 151c. Furthermore, the control electrode
of the first switch 153 (the gate electrode of the FET) and
the input voltage of the second power supply unit 15
function as a first switch controller that controls the ON
(closed state) and OFF (open state) of the first switch 153.
Further, the number of capacitors of the second power
supply unit 15 is preferably two or more, but is not limited
to a particular number. Furthermore, the first switch and
the first switch controller preferably turns the first
switch off (an open state) when the voltage inputted to the
second power supply unit 15 is higher than a predetermined
voltage, and turns the first switch on (a closed state) when
the voltage inputted to the second power supply unit 15 is
equal to or lower than the predetermined voltage. The first
switch is not limited to the FET. For example, it may be a
switch that is controlled by a microcomputer.
In accordance with the configuration of the first
embodiment, energy loss due to thermal conversion is
considerably small compared to that of the conventional
example constructed with the constant voltage circuit using
a Zener diode, thereby reducing the standby power of the
load control device 1A. Therefore, in the state in which
the load 3 is turned off, the current flowing into the load
3 via the second power supply unit 15 is further reduced,
and the erroneous operation of the load {the erroneous light
emission of an LED lamp) can be prevented even when a load,
such as an LED lamp which has no countermeasure against
noise, is connected.
(Second Embodiment)
A two-wire load control device IB in accordance with a
second embodiment of the present invention will be described
with reference to Figs. 3 and 4. Fig. 3 is a circuit
diagram showing the configuration of the two-wire load
control device IB, and Fig. 4 is a timing chart showing the
voltage and operation of each component. The second power
supply unit 15 of the load control device IB is configured
such that a voltage clamp circuit (a constant voltage
circuit) including a Zener diode (a constant voltage diode}
154 and a semiconductor switch device 155 is connected with
a front end of a plurality of diodes 151a to 151c that are
connected in series to clamp an input voltage, in addition
to the configuration of the first embodiment.
The square wave voltage based on the Zener voltage of
the Zener diode 154 is outputted from the voltage clamp
circuit, and the first switch 153 is turned on and off
almost in synchronization with the square wave. When the
first switch 153 becomes ON (a closed state), the voltage
outputted from the voltage clamp circuit is almost OV, and
thus only charges discharged from the capacitors 151a to
151c are supplied to the first power supply unit 14. The
voltage outputted from the second power supply unit 15 forms
a substantial square wave that has the voltage obtained by
dividing the peak voltage of input voltage by the number of
capacitors, as its peak voltage.
The second power supply unit 15 in accordance with the
second embodiment includes the voltage clamp circuit
(constant voltage circuit) including the Zener diode 154 and
the semiconductor switch device 155, as the conventional
example. However, the current outputted from the voltage
clamp circuit is used only to charge the capacitors 151a to
151c and does not flow directly into the first power supply
unit 14, and thus the value of the current flowing through
the clamp circuit is very small. Further, the output
voltage of the voltage clamp circuit is divided and stepped
down by the plurality of capacitors 151a to 151c.
Accordingly, compared to the conventional example, the Zener
voltage of the Zener diode 154 can be increased, and energy
loss due to thermal conversion is further reduced.
Furthermore, different from the configuration of the first
embodiment, the voltage applied to parts, such as capacitors
diodes or the like, is stepped down by the voltage clamp
circuit, thereby ensuring the withstanding voltage of the
parts.
(Third Embodiment)
A two-wire load control device 1C in accordance with a
third embodiment of the present invention will be described
with reference to Fig. 5. Fig. 5 is a circuit diagram
showing the configuration of the two-wire load control
device 1C. In the third embodiment, a series/parallel
switching circuit for switching between the series and
parallel connections of a first switch 153 and a plurality
of capacitors and a control unit thereof are implemented
using ICs. The series/parallel switching circuit includes a
second switch 15 6 connected to the terminals of the
capacitors 151a to 151c and configured to switch between the
series and parallel connections of the capacitors, and a
second switch controller 157 configured to control the
connection status of the second switch 156. The second
switch controller 157 may also function as a first switch
controller that controls the ON (closed state) and OFF {open
state) of the first switch.
Further, when the number of capacitors is three or
more, the second switch controller 157 may be configured to
arbitrarily vary the number of capacitors that are connected
in series. Alternatively, a peak voltage detection unit 158
may be provided to detect a peak voltage of the voltage
inputted from the commercial power source 2 or the
rectifying unit 12, thereby automatically varying the number
of capacitors that are connected in series according to,
e.g., the peak voltage of the input voltage. As is well
known, the voltages of commercial power source 2 are
classified into a 100 to 120V system and a 200 to 240V
system. In accordance with this configuration, the same
load control device 1C may be used in different voltage
systems, such as a 100V system, a 200V system and the like,
which are commercial powers.
Further, when the second switch controller 157 also
functions as the first switch controller, the time for which
the first switch 153 is opened may be controlled based on
the peak voltage of the peak voltage detection unit 158.
Alternatively, an output voltage detection unit 162 (see
Fig. 7) may be provided to detect the voltage outputted from
the second power supply unit 15 to the first power supply
unit 14 and to control the time for which the first switch
153 is opened based on the output voltage of the second
power supply unit 15.
For example, when the voltage inputted to the second
power supply unit 15 or the voltage outputted from the
second power supply unit 15 is higher than a predetermined
threshold value, control is performed such that the time for
which the first switch 153 is opened is reduced, thereby
controlling the amount of current outputted from the second
power supply unit 15 to be constant. Further, it may be
configured to vary the threshold value depending on the peak
voltage.
(Other Modifications)
Fig. 6 shows the configuration of a two-wire load
control device ID in accordance with a modification of the
second embodiment shown in Fig. 3. In this modification,
when the number of capacitors that are connected in series
is three or more, a third switch 159 is connected in
parallel to at least one of the plurality of capacitors 151a
to 151c, and a third switch controller 160 configured to
control the ON (closed state) and OFF (open state) of the
third switch 159 is provided. With this, the number of
capacitors connected in series can be varied. Further, the
peak voltage detection unit 158 may be provided to detect
the peak voltage of the voltage inputted from a commercial
power source 2 or a rectifying unit 12 and to automatically
vary the number of capacitors that are connected in series
based on the peak voltage of the input voltage.
Fig. 7 is a circuit diagram showing the configuration
of a two-wire load control device IE in accordance with
another modification. In the two-wire load control device
IE, a current limiting device 161, such as a resistor or the
like, is connected in series to the series circuit of a
plurality of capacitors 151a to 151c. The current with
which the capacitors 151a to 151c are charged may be limited
by the current limiting device 161. Further, the amount of
current is varied by using a variable resistor as the
current limiting device 161, and an output voltage detection
unit 162 is provided to detect the voltage outputted from
the second power supply unit 15 to the first power supply
unit 14. Further, a current limiting device controller 163
is provided to control the amount of current varied by the
current limiting device 161.
With this configuration, the amount of current is
controlled by the current limiting device 161 based on the
voltage outputted from the second power supply unit 15.
Furthermore, although Fig. 7 is illustrated based on the
configuration of the second embodiment shown in Fig. 3, it
is not limited to the modification of the second embodiment,
but the current limiting device may be added to the
configuration of other embodiments (this is the same for the
following modified embodiments, as long as there is no
special incompatibility) .
Fig. 8 is a circuit diagram showing the configuration
of a two-wire load control device 1F in accordance with
still another modification.
In the two-wire load control device 1F, a plurality of
Zener diodes 154a and 154b (whose number is not limited to
two) that are connected in series is used as the Zener
diodes of a voltage clamp circuit, and the intermediate
voltage of Zener voltage is inputted to the output terminal
15b of a second power supply unit 15. While the current
flowing through the Zener diodes of the voltage clamp
circuit flows into the load 3 via the ground, the current
flowing into the load 3 may be reduced by causing a part of
the current to flow into a first power supply unit 14.
Fig. 9 is a circuit diagram showing the configuration
of a two-wire load control device 1G in accordance with
still another modification.
In the two-wire load control device 1F, a plurality of
Zener diodes 154a and 154b (whose number is not limited to
two) that are connected in series is used as the Zener
diodes of a voltage clamp circuit, and a switch device 164
connected in parallel to at least one (e.g., the Zener diode
154b) of the Zener diodes and a fourth switch controller 165
configured to control the ON (closed state) and OFF {open
state) of the switch device 164 are provided. In accordance
with this configuration, Zener voltage may be converted
based on the peak voltage of a commercial power source 2 to
which the two-wire load control device 1G is connected, and
thus the voltage output from the voltage clamp circuit may
be converted to a constant value or an arbitrary value.
Further, although in each of the embodiments, the
constant voltage circuit including the Zener diode and the
semiconductor switch device has been illustrated as the
voltage clamp circuit, the prevent invention is not limited
thereto, but any one of other step-down circuits using a
transformer or a capacitor may be used. Further, a
plurality of sets of series circuits of a plurality of
capacitors may be provided and the series and parallel
connections of the plurality of sets of series circuits of
the plurality of capacitors may be switched. Furthermore,
the rectifying unit 12 is not necessarily a full-wave
rectifier circuit, but may be a half-wave rectifier circuit.
If the rectifying unit 12 is a half-wave rectifier circuit,
the same effect can be achieved by providing two sets of
half-wave rectifier circuits and second power supply units
and connecting the two sets of half-wave rectifier circuits
and second power supply units in parallel, thereby shifting
the phase of current flowing through each of the circuits by
a half period. Alternatively, it may be possible to be
configured to connect a plurality of second power supply
units in series.
While the invention has been shown and described with
respect to the embodiments, the present invention is not
limited to the above-described embodiments, and 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 a commercial power source and a load, comprising:
an off power supply unit configured to acquire an
internal power when the load is turned off,
wherein the off power supply unit includes a plurality
of capacitors of which series and parallel connections are
switched based on a level of input voltage, and
wherein charging and discharging of the plurality of
the capacitors are repeated and a power obtained by
discharging of the plurality of capacitors is used as the
internal power.
2. A two-wire load control device connected in series
between a commercial power source and a load, comprising:
a primary switching unit configured such that main
electrodes of a main switch device are connected in series
to the commercial power source and the load, and configured
to control power supply to load;
a rectifying unit connected between the main
electrodes of the main switch device;
a control unit configured to control ON and OFF of the
load in response to a signal from an outside;
a first power supply unit configured to reliably
supply a power to the control unit;
a second power supply unit configured to supply a
power to the first power supply unit when a power is
supplied from both ends of the primary switching unit via
the rectifying unit and the load is turned off; and
a third power supply unit configured to supply power
to the first power supply unit when a power is supplied from
both ends of the primary switching unit via the rectifying
unit and the load is turned on;
wherein the first power supply unit is a DC/DC
converter configured to step down an input DC current so
that an output voltage decreases below an input voltage;
wherein the second power supply unit includes a
plurality of capacitors, a series/parallel switching circuit
configured to switch between series and parallel connections
of the plurality of capacitors, a first switch connected to
an output terminal for the first power supply unit and a
first switch controller configured to control ON (a closed
state) and OFF (an open state) of the first switch;
wherein when a voltage inputted to the second power
supply unit is higher than a predetermined voltage, the
series/parallel switching circuit allows the plurality of
capacitors to be connected in series and charge the
plurality of capacitors, and the first switch controller
turns the first switch off (an open state); and
wherein when the voltage inputted to the second power
supply unit is equal to or lower than the predetermined
voltage, the series/parallel switching circuit allows the
plurality of capacitors to be connected in parallel and
discharge the plurality of capacitors, and the first switch
controller turns the first switch on (a closed state), so
that charging and discharging of the plurality of capacitors
are repeated, thereby stepping down the voltage inputted
from the rectifying unit to a predetermined level and then
outputting resulting voltage.
3. The two-wire load control device of claim 2, wherein
the second power supply unit further includes a voltage
clamp circuit configured to clamp the voltage inputted from
the rectifying unit to a predetermined value, thereby
preventing a voltage above the predetermined voltage from
being applied to the plurality of capacitors that are
connected in series.
4. The two-wire load control device of claim 2 or 3,
wherein the series/parallel switching circuit includes a
second switch connected to terminals of the plurality of
capacitors and configured to switch between series and
parallel connections of the plurality of capacitors and a
second switch controller configured to control a connection
state of the second switch.
5. The two-wire load control device of claim 4, wherein
the plurality of capacitors is three or more in number, and
the second switch controller varies the number of the
plurality of capacitors that are connected in series.
6. The two-wire load control device of claim 5, wherein
the second power supply unit further includes a peak voltage
detection unit configured to detect a peak voltage of
voltage from the commercial power source or the rectifying
unit, and
the second switch controller varies the number of the
plurality of capacitors that are connected in series by the
second switch based on a peak voltage of the commercial
power source.
7. The two-wire load control device of any one of claims 2
to 4, wherein the series/parallel switching circuit includes
first diodes connected in series between the plurality of
capacitors and second diodes connected such that a current
flows in an opposite direction to a direction in which the
current flows during the charging.
8. The two-wire load control device of claim 7, wherein
the plurality of capacitors is three or more in number, the
second power supply unit further includes a third switch
connected in parallel to at least one of the plurality of
capacitors and a third switch controller configured to
control ON (a closed state) and OFF (an open state) of the
third switch, and the number of the plurality of capacitors
connected in series is varied by controlling the ON (closed
state) and OFF (open state) of the third switch.
9. The two-wire load control device of claim 8, wherein
the second power supply unit further includes a peak voltage
detection unit configured to detect a peak voltage of
voltage inputted from the commercial power source or the
rectifying unit, and the third switch controller varies the
number of the plurality of capacitors connected in series by
the third switch based on the peak voltage of the commercial
power source.
10. The two-wire load control device of any one of claims 2
to 9, wherein the second power supply unit further includes
a current limiting device configured to limit an amount of
current with which the plurality of capacitors is charged
when the plurality of capacitors are connected in series.
11. The two-wire load control device of claim 10, wherein
the current limiting device varies the amount of current,
the second power supply unit further includes an
output voltage detection unit configured to detect a voltage
outputted from the second power supply unit to the first
power supply unit and a current limiting device controller
configured to control the amount of current by the current
limiting device, and
the current limiting device controller controls the
amount of current by the current limiting device based on
the voltage outputted from the second power supply unit
which is detected by the output voltage detection unit.
12. The two-wire load control device of claim 2 or 3,
wherein the second power supply unit further includes a peak
voltage detection unit configured to detect a peak voltage
of voltage inputted from the commercial power source or the
rectifying unit, and the first switch controller controls a
time for which the first switch is opened based on the peak
voltage.
13. The two-wire load control device of claim 2, wherein
the first switch and the first switch controller are formed
of semiconductor devices configured to be conductive in
response to an input of a predetermined control signal, and
a voltage outputted from the rectifying unit is inputted to
the semiconductor devices as the control signal.
14. The two-wire load control device of claim 3, wherein
the first switch and the first switch controller are formed
of semiconductor devices configured to be conductive in
response to input of a predetermined control signal, and a
voltage outputted from the voltage clamp circuit is inputted
to the semiconductor devices as the control signal.
15. The two-wire load control device of claim 12, wherein
the second power supply unit further includes an output
voltage detection unit configured to detect a voltage
outputted from the second power supply unit to the first
power supply unit, and
the first switch controller controls a time for which
the first switch is opened based on the voltage outputted
from the second power supply unit.
16. The two-wire load control device of claim 3, wherein
the voltage clamp circuit includes a plurality of constant
voltage diodes that are connected in series, and an
intermediate conjunction of the plurality of constant
voltage diodes connected in series is connected to an input
unit of the first power supply unit, so that a part of
current to flow the plurality of constant voltage diodes
connected in series is caused to flow into the first power
supply unit.
17. The two-wire load control device of claim 3, wherein
the voltage clamp circuit includes a plurality of constant
voltage diodes connected in series and a switch device
connected in parallel to at least one of the constant
voltage diodes,
the load control device further comprises a peak
voltage detection unit configured to detect a peak voltage
of voltage inputted from the commercial power source or the
rectifying unit and a fourth switch controller configured to
control ON (a closed state) and OFF (an open state) of the
switch device, and
the fourth switch controller varies a voltage of the
constant voltage diode based on the peak voltage.