JP2013109641A - Two-wire system load control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-wire system load control device capable of dealing with various uses from a load through which heavy current flows to a load through which only minute current flows.SOLUTION: A two-wire system load control device includes a first switch element 12 for a large current load such as a latch type relay, and a second switch element 30 for a small current load such as a triac, and a load current value detection part 34. First, the second switch element 30 is used to turn on a load 3, and when a load current value becomes a predetermined threshold or more, it is switched to the first switch element 12 while the load 3 is continuously to be turned on.

Description

  The present invention relates to a two-wire load control device for controlling on and off of a load such as a lighting device.

  2. Description of the Related Art Conventionally, a load control device using a semiconductor switch element such as a triac for controlling on and off of a lighting device or the like is known. Among such load control devices using semiconductor switch elements, the two-wire load control device is connected in series between the AC power source and the load, and therefore wiring work is simple. On the other hand, it is necessary to secure a power source for driving the semiconductor switch element and the control circuit (CPU or the like) even when the load is turned off. Therefore, even when a rectifier circuit is connected in parallel to the semiconductor switch element and the load is turned off, a weak current that does not actually turn on or malfunction is passed through the load, and the buffered capacitor is charged with the rectified current, The power supply when the load is off (off power supply unit) is secured. On the other hand, even when the load is turned on, after the semiconductor switch element self-extinguishes at the zero crossing point of the AC power supply, until the voltage of the AC power supply reaches the gate drive voltage of the semiconductor switch element, The open / close portion of the semiconductor switch element is not conductive. Therefore, during that time, the current flowing from the AC power source to the load flows through the rectifier circuit. Therefore, by charging the buffer capacitor with the rectified DC power, a power supply (on power supply unit) when the load is on is secured (see Patent Document 1).

  There are various types of lighting devices such as a chandelier type that uses many incandescent bulbs, a fluorescent lamp, and an LED bulb. A semiconductor switch element such as a triac requires a small amount of power to control conduction and non-conduction (switching), and the semiconductor switch element can be driven by the power charged in the buffer capacitor as described above. On the other hand, the semiconductor switch element is not very suitable for a load that requires a large current because of the large power loss due to the switching part. On the other hand, a switch element having a mechanically driven switching contact, such as a latch relay, has a small power loss due to its switching part and is suitable for a load that requires a large current. On the other hand, in order to make the mechanical switching contact conductive and non-conductive, it is necessary to drive an electromagnet device, for example, and it cannot be switched at high speed, and the switch element as described above is temporarily made nonconductive. In such a case, it is not possible to use an on-power supply unit that secures electric power in the meantime. Therefore, a separate power source using a current transformer or the like is required.

JP 2008-97535 A

  The present invention has been made to solve the above-described problems of the conventional example, and is a two-wire load capable of controlling on and off of various loads from a load through which a large current flows to a load through which only a small current flows. An object is to provide a control device.

In order to achieve the above object, a two-wire load control device according to the present invention includes:
Two input terminals respectively connected to an AC power source and a load;
A first switch element connected between the two input terminals;
A second switch element connected in parallel with the first switch element between the two input terminals, the allowable load current of which is smaller than the allowable load current of the first switch element;
An off-power supply unit that secures DC power using an AC current flowing from the AC power source through the load when the first switch element and the second switch element are not conducted together;
An on-power supply unit that secures direct-current power using alternating current flowing from the alternating-current power supply through the load when either the first switch element or the second switch element is made conductive;
Controlled on and off of the first switch element and the second switch element based on operation information input from the outside, driven by DC power output from the off power source and on power source And a control unit that selects and conducts either the first switch element or the second switch element when the load is turned on.

  Further, the control unit detects a load current value flowing from the AC power source to the load when the load is on, and the switch element that is currently conducted is appropriate for the detected load current value. When it is determined that the switch element that is currently conducting is inappropriate for the detected load current value, the switch element that is currently conducting is made non-conductive and the other switch element is made conductive. It is preferable to make it.

  Alternatively, it is preferable that the control unit selects one of the first switch element and the second switch element when turning on the load based on the operation information.

Further, the first switch element is a relay type switch element provided with a switching contact that is mechanically opened and closed,
The second switch element is a semiconductor switch element that does not include a mechanically opened / closed contact,
A current transformer is connected between one of the switching contacts of the first switch element and one of the two input terminals;
The on-power supply unit is
A first on-power supply unit connected to a secondary side of the current transformer and securing a DC power using an alternating current flowing on the secondary side of the current transformer;
It is preferable to include a second on-power supply unit that is connected to the opening / closing unit of the second switch element and secures DC power using an AC current flowing from the AC power source through the load.

  Also, a first auxiliary power supply unit that is provided between the off power supply unit or the on power supply unit and the control unit and supplies DC power to the control unit, and the first switch element is changed from a non-conductive state to a conductive state. It is preferable to further include a second auxiliary power supply unit that supplies DC power for driving the first switch element when switched.

The control unit includes a plurality of control circuits having different drive voltages,
The off power supply unit and the on power supply unit each have a plurality of voltage systems with different drive voltages corresponding to the drive voltages of the plurality of control circuits,
The first auxiliary power supply unit is provided in a voltage system having a high drive voltage among the plurality of voltage systems, and the second auxiliary power supply unit is provided in a voltage system having a low drive voltage among the plurality of voltage systems. It is preferable that

  In addition, it is preferable that the first auxiliary power supply unit and the second auxiliary power supply unit include a storage element that is received by DC power output from the off power supply unit or the on power supply unit.

  According to the above configuration, when a large current flows when the load is turned on, such as a chandelier type lighting device, the first switch element having a large load current allowance is made conductive, and the load is a fluorescent lamp, When the current flowing when the load is turned on is not so large as in an illumination device using an LED bulb or the like, the second switch element having a small load current allowance can be made conductive. Thereby, the two-wire load control device can be applied to various types of loads.

1 is a block diagram showing a basic configuration of a two-wire load control device according to an embodiment of the present invention. The circuit diagram which shows the specific structure of the said 2-wire type load control apparatus. FIG. 6 is a waveform diagram of voltages at various parts when a small current load is controlled by the two-wire load control device. The waveform diagram of the voltage of each part etc. in the case of controlling a large current load with the said 2 wire type load control apparatus. The wave form diagram which shows the role sharing of the OFF power supply part, 1st ON power supply part, and 2nd ON power supply part in the case of controlling a small current load with the said 2 wire type load control apparatus.

  A two-wire load control apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a basic block configuration of a two-wire load control device 1 (hereinafter simply referred to as load control device 1) according to the present embodiment, and FIG. 2 shows a specific circuit configuration. The load control device 1 includes two input terminals 11a and 11b connected to an AC power supply 2 and a load 3, respectively, and a first switch element 12 and a current transformer 13 connected between the two input terminals 11a and 11b. The second switch element 30 is connected to the open / close section of the first switch element 12 in parallel. In the present embodiment, the first switch element 12 is a relay type switch element having a mechanically driven switching contact such as a latch type relay, and the second switch element 30 is a semiconductor switch element such as a triac. .

  The first switch element 12 and the second switch element 30 are both in a non-conducting state by using an alternating current flowing from the alternating current power supply 2 through the load 3 to both terminals 30a and 30b of the opening and closing part of the second switch element 30. An off power supply unit 14 that outputs DC power is sometimes connected. More specifically, both terminals 30a and 30b of the opening / closing part of the second switch element 30 are configured by diode bridges or the like, and an alternating current flowing from the alternating current power supply 2 through the load 3 is converted into a direct current (pulsating flow). A first rectifier circuit 15 to be converted is connected in parallel. For example, a resistor that limits current, a Zener diode (constant voltage diode) that clamps a voltage, and a constant voltage circuit (bootstrap circuit) 16 that includes transistors are connected to the first rectifier circuit 15. . The first rectifier circuit 15 and the constant voltage circuit 16 constitute an off power supply unit 14. In the circuit configuration shown in FIG. 2, the off power supply unit 14 has two voltage systems, for example, a high voltage system with a drive voltage of 24V and a low voltage system with a drive voltage of 12V.

  Both the first switch element 12 and the second switch element 30 are non-conductive, and the first rectifier circuit 15 is connected to both terminals 30a and 30b of the opening / closing part of the second switch element 30 even when the load 3 is in the OFF state. Is connected, a weak current flows through the series circuit of the AC power supply 2, the load 3, and the first rectifier circuit 15. The current at this time is a minute current that does not cause the load 3 to malfunction, and is set so that the impedance of the off-power supply unit 14 becomes high. When a full-wave rectified pulsating current is input from the first rectifier circuit 15, the voltage waveform of the output from the off power supply unit 14 becomes substantially trapezoidal due to the Zener voltage of the Zener diode. Part of the current output from the off power supply unit 14 is stepped down by the regulator and supplied to the first control unit 21. In parallel with this, the buffer capacitor of the auxiliary power supply unit (first auxiliary power supply unit) 23 for operating the CPU is charged. When the voltage of the pulsating current rectified by the first rectifier circuit 15 is lower than the Zener voltage, the buffer capacitor of the auxiliary power supply unit 23 becomes a power source and supplies power to the first control unit 21 via the regulator. To do. Therefore, when the load 3 is in the off state, the buffer capacitor of the auxiliary power supply unit 23 is repeatedly charged and discharged. Similarly, a part of the current output from the off power supply unit 14 is supplied to the second control unit 22, and in parallel therewith, the buffer of the auxiliary power supply unit for opening / closing contacts (second auxiliary power supply unit) 24. Charge the capacitor.

  The secondary side of the current transformer 13 is supplied with direct current power when the on / off of the load 3 is controlled using the first switch element 12 using the alternating current flowing through the secondary side of the current transformer 13. A first on-power supply unit 17 for securing is connected. More specifically, a second rectifier circuit 18 configured by a diode bridge or the like and converting an alternating current flowing from the alternating current power supply 2 via the load 3 into a direct current (pulsating flow) is connected. The second rectifier circuit 18 is connected to a constant voltage circuit 19 composed of a capacitor and a Zener diode. The first ON power supply unit 17 also has two voltage systems, for example, a high voltage system with a driving voltage of 24V and a low voltage system with a driving voltage of 12V. The output terminal of the high voltage system of the off power supply unit 14 and the output terminal of the high voltage system of the on power supply unit 17 are connected to each other via a backflow prevention diode. Similarly, the output terminal of the low voltage system of the off power supply unit 14 and the output terminal of the low voltage system of the on power supply unit 17 are connected to each other through a backflow preventing diode.

  On the other hand, a thyristor is connected to the first rectifier circuit 15 as the third switch element 32. The first rectifier circuit 15 is connected to a power supply circuit 33 including switch elements 35 and 36 such as transistors and a Zener diode 37. The first rectifier circuit 15 and the power supply circuit 33 function as a second ON power supply unit 31 for securing DC power when the second switch element 30 or the third switch element 32 is turned on to turn on the load 3. In FIG. 2, the anode of the thyristor 32 is connected to one input terminal of the diode bridge constituting the first rectifier circuit 15, and the cathode of the thyristor 32 is grounded. In the configuration example shown in FIG. 2, the second ON power supply unit 31 has only the output terminal of the low voltage system.

  As described above, the load control device 1 includes, as main switch elements, the first switch element 12 that is a relay-type switch element having a mechanically driven switching contact and the first switch element that is a semiconductor switch element such as a triac. Two switch elements 30 are provided. The switching contact of the relay type switch element is opened and closed by, for example, an electromagnet, and the allowable load current value is large. That is, the load current that the first switch element 12 can tolerate is large, which is suitable for controlling on / off of a load through which a large current flows. On the other hand, a large amount of electric power is required to open and close the open / close contact of the first switch element 12, and the open / close contact may open and close carelessly due to an impact or the like. On the other hand, the triac can also flow a relatively large current, but the allowable load current value is smaller than that of a mechanical switching contact. In addition, if a current exceeding the specification range flows in the triac for a long time, it may cause abnormal heat generation or failure. On the other hand, since there are no movable parts in the triac, the switching contacts do not open and close carelessly due to impact or the like. Accordingly, the load control device 1 detects the value of the current flowing through the load 3, selects either the first switch element 12 or the second switch element 30, and controls the on / off of the load 3.

  A load current value detector 34 composed of a resistor and a capacitor is connected to the output terminal of the high voltage system of the first ON power supply unit 17, and a voltage between terminals of the capacitor (higher or lower than the threshold voltage). Level) is input to the first control unit 21. Even when the open / close sections of the first switch element 12 and the second switch element 30 are non-conductive, current flows from the first rectifier circuit 15 of the off power supply section 14 to the primary side of the current transformer 13. However, the current flowing at this time is a weak current that does not cause the load 3 to malfunction, and the amount of current that flows on the secondary side of the current transformer 13 is further small and almost negligible. On the other hand, when the opening / closing part of the first switch element 12 or the second switch element 30 is conducted, that is, when the load 3 is turned on, a current sufficient to drive the load 3 flows to the primary side of the current transformer 13, Along with this, the amount of current flowing on the secondary side of the current transformer 13 also increases. The current flowing on the secondary side of the current transformer 13 is full-wave rectified by the second rectifier circuit 18 and charges the capacitor of the first on-power supply unit 17. The first control unit 21 detects a rough load current value from the voltage across the capacitors of the first ON power supply unit 17. Then, the first control unit 21 determines which of the first switch element 12 and the second switch element 30 should be conducted based on the detected load current value, and outputs a drive signal corresponding to the determination result. .

  For example, when the user operates an input unit 25 such as an operation handle or a remote control device provided on the wall surface, the control unit 20 controls conduction and non-conduction of the first switch element 12 according to the operation information. The control unit 20 includes, for example, a CPU and the like, and includes a first control unit (control circuit having a low drive voltage) 21 driven by a low voltage (for example, 3V) and a second control driven by a high voltage (for example, 24V). Part (control circuit with a high driving voltage) 22 is provided. The first control unit 21 is connected to the output terminals of the low voltage system of the off power supply unit 14 and the first on power supply unit 17 through a regulator. The regulator is for stepping down the drive voltage 12V of the low voltage system to a lower voltage, for example, about 3V. The second control unit 22 outputs a large amount of power for driving the electromagnet device of the latching relay that constitutes the first switch element 12.

  Further, an auxiliary power supply unit 23 for operating the CPU is connected between the output terminals of the low voltage system of the off power supply unit 14 and the first on power supply unit 17 and the first control unit 21 via a regulator. In addition, an auxiliary power supply unit 24 for opening and closing the contact of the first switch element 12 is connected between the output terminals of the high voltage system of the off power supply unit 14 and the first on power supply unit 17 and the second control unit 22. . Each of the auxiliary power supply unit 23 for operating the CPU and the auxiliary power supply unit 24 for opening and closing the contacts is composed of a buffer capacitor or the like.

  Next, the operation of the load control device 1 according to this embodiment will be described. When the operation information for turning on the load 3 is input from the input unit 25, the first control unit 21 first turns on the load 3 using the second switch element 30. That is, the first control unit 21 outputs a gate drive signal, whereby the switch element 35 of the second ON power supply unit 31 is turned on, and the switch element 36 is turned on. As a result, the current output from the first rectifier circuit 15 flows through the switch element 36 and charges the buffer capacitor of the auxiliary power supply unit 23. When the output voltage from the first rectifier circuit 15 becomes higher than the zener voltage of the zener diode 37, the third switch element 32, which is a thyristor, becomes conductive and current starts to flow to the load 3. Since this current also flows through the gate of the second switch element 30 that is a triac, when the voltage becomes higher than the trigger voltage of the triac, the triac, that is, the second switch element 30 becomes conductive. Once the second switch element 30 is turned on, the current continues to flow. However, when the voltage of the AC power source reaches the zero cross point, the triac and the thyristor self-extinguish, and the second switch element 30 and the third switch element 32 are not turned on. It becomes conductive. When the second switch element 30 is turned off, a current flows from the first rectifier circuit 15 through the power supply circuit 33 to the auxiliary power supply unit 23, and an operation for securing the self-circuit power supply of the load control device 1 is performed. That is, every half cycle of alternating current, the self-circuit power supply of the load control device 1 is secured, the third switch element 32 is turned on, the second switch element 30 is turned on, and the second switch element 30 and the third switch element 32 are turned on. Arc extinction is repeated.

  FIG. 3 is a waveform diagram of voltages at various parts when the load current value is smaller than a predetermined threshold value and the load 3 is turned on using the second switch element 30 and the third switch element 32. In this case, the load current value detected by the load current value detection unit 34 is equal to or less than a predetermined threshold value, and the first switch element 12 is not used. Therefore, the first switch element 12 remains non-conductive. In the state where the load 3 is off, the voltage of the AC power source is applied as it is between the terminals of the opening / closing part of the second switch element 30. When a gate drive signal is output from the first control unit 21 to the switch element 35 of the power supply circuit 33 (load on timing in FIG. 3), the current rectified by the first rectifier circuit 15 is the off-power supply unit. 14 constant voltage circuit 16 is commutated to power supply circuit 33 of second on power supply unit 31. As described above, the third switch element 32 that is a thyristor is turned on with a slight delay, and the second switch element 30 that is a triac is turned on with a little delay. Since both the thyristor and the triac are self-extinguishing type switch elements, the second switch element 30 and the third switch element 32 become non-conductive at the zero cross point of the AC power supply. When the second switch element 30 becomes conductive and a load current flows through the load 3, a current flows through the secondary side of the current transformer 13, and the load current value detector 34 detects this load current value. Unless the load current value detected by the load current value detection unit 34 exceeds a predetermined threshold value, the second switch element 30 and the third switch until the operation information for turning off the load 3 is input from the input unit 25. The conduction and non-conduction of the element 32 are repeated.

  FIG. 4 shows a waveform diagram of voltages at various portions when the load current value is larger than a predetermined threshold and the load 3 is turned on exclusively using the first switch element 12. Also in this case, first, similarly to the above, the third switch element 32 that is a thyristor and the second switch element 30 that is a triac are first conducted. When the second switch element 30 is turned on and a load current flows through the load 3, the load current value detector 34 detects this current value. In this case, since the load current value detected by the load current value detection unit 34 is equal to or greater than a predetermined threshold, the first control unit 21 makes the first switch element 12 conductive to the second control unit 22. The control signal is output. In response to the control signal, the second control unit 22 outputs drive power to, for example, an electromagnet device in order to switch the open / close contact of the first switch element 12 from the non-conductive state to the conductive state. This driving power is provided by discharging the buffer capacitor of the auxiliary power supply unit 24. Thereby, the switching contact of the first switch element 12 is conducted. When the open / close contact of the first switch element 12 is turned on, its electrical resistance is much smaller than the electrical resistance of the second switch element 30, so that the current flows exclusively through the first switch element 12, and the second switch element 12 30 hardly flows. Accordingly, DC power is not output from the second ON power supply unit 31, and the power of the control unit 20 is supplied from the first ON power supply unit 17.

  In the waveform of the current between the first and second switch element terminals in FIG. 4, the first wave is due to the second switch element 30, and the second and subsequent waves are due to the first switch element 12. In FIG. 4, the load current value is compared with the threshold value within a half cycle of the AC power supply, but this is for the convenience of drawing. Actually, since it takes a certain time (for example, several seconds to several tens of seconds) for the load current to stabilize after the load 3 is turned on, the load current value is detected and the detected load current value is compared with a predetermined threshold value. Is performed after the load current is stabilized. Therefore, the second switch element 30 that is a triac and the third switch element 32 that is a thyristor repeat conduction and non-conduction for a certain time until the load current is stabilized.

  FIG. 5 is a waveform diagram of FIG. 3 in which roles of the off power supply unit 14, the first on power supply unit 17, and the second on power supply unit 31 are added. Until the load 3 is turned on, the DC power of the control unit 20 is held by the off power supply unit 14. When a gate drive signal is output from the first control unit 21 to the switch element 35 of the power supply circuit 33 in order to turn on the load 3, the second on power supply unit 31 is triac from the zero cross point (voltage 0 V) of the AC power supply. DC power is output only until a certain second switch element 30 is turned on. On the other hand, the first on-power supply unit 17 starts output of DC power when the second switch element 30 that is a triac first conducts and the load current begins to flow to the load 3, and the DC power is output until the load 3 is turned off. Continue to output power.

  As described above, the load control device 1 includes the first switch element 12 that is a relay-type switch element having a mechanically driven switching contact and the second switch element 30 that is a semiconductor switch element such as a triac. Yes. As described above, a semiconductor switch element such as a triac is not very suitable for a load that requires a large current because of a large power loss due to its opening / closing portion. On the other hand, a switch element having a mechanically driven switching contact, such as a latch relay, has a small power loss due to its switching part and is suitable for a load that requires a large current. Therefore, by selecting and using either the first switch element 12 or the second switch element 30 according to the load current value, it is possible to cope with various on / off control of the load. Further, in order to switch the mechanical switching contacts, it is necessary to drive, for example, an electromagnet device, which cannot be switched at high speed, and the switch element is temporarily made non-conductive to secure electric power in the meantime. Such a second ON power supply unit 31 cannot be used. However, since the load control device 1 includes the first on-power supply unit 17 connected to the secondary side of the current transformer 13, the load control device 1 is a case where the load 3 is turned on using the first switch element 12. However, the power supply of the control unit 20 can be secured. Furthermore, when a large current flows through the load 3, that is, when the load current value is large, a large current flows through the primary side of the current transformer 13, and therefore the current transformer 13 may be affected by problems such as heat generation and size of the current transformer 13. The primary side impedance cannot be increased. Therefore, when the current flowing through the load (load current value) is small, the current value flowing through the secondary side of the current transformer is small, and there is a possibility that sufficient power cannot be secured. However, when the load current value is small, the power supply of the control unit 20 can be secured by the second ON power supply unit 31 by using the second switch element 30. Furthermore, since a switch element having a mechanically driven switching contact cannot perform so-called zero-cross switching, it has problems such as arcing when the switching contact is opened and closed, and noise associated therewith. However, even when the load 3 is turned on / off using the first switch element 12, the second switch element 30 is turned on before the first switch element 12 and the second switch element 12 is turned on after the first switch element 12. By making the two switch elements 30 non-conductive, zero cross switching can be performed.

  In the description of the embodiment, the first control unit 21 selects one of the first switch element 12 and the second switch element 30 based on the load current value detected by the load current value detection unit 34. Although an example configured as described above is shown, the present invention is not limited to this. The first control unit 21 may be configured to select either the first switch element 12 or the second switch element 30 according to the operation information input from the input unit 25. For example, when the operation information from the input unit 25 is brightness information of the lighting device, the first switch element 12 is selected when the lighting device is turned on with high luminance, and the second switch element is turned on when the lighting device is turned on with low luminance. 30 can be configured to select.

  Further, even when the second switch element 30 is used, since the DC power is output from the first ON power supply unit 17, the second ON power supply unit 31 can be omitted. In that case, a gate drive signal is directly output from the first control unit 21 to the second switch element 30 that is a triac and the third switch element 32 that is a thyristor. Further, the triac is exemplified as the second switch element 30, but the present invention is not limited to this, and other semiconductor switch elements, for example, an antiparallel connection of two thyristors may be used.

DESCRIPTION OF SYMBOLS 1 Two-wire type load control apparatus 2 AC power supply 3 Load 11a, 11b Input terminal 12 1st switch element (relay type switch element)
DESCRIPTION OF SYMBOLS 13 Current transformer 14 OFF power supply part 15 1st rectifier circuit 16 Constant voltage circuit 17 1st ON power supply part 18 2nd rectifier circuit 19 Constant voltage circuit 20 Control part 21 1st control part 22 2nd control part 23 For CPU operation | movement Auxiliary power supply (first auxiliary power supply)
24 Auxiliary power supply for opening and closing contacts (second auxiliary power supply)
25 Input unit 30 Second switch element (triac or semiconductor switch element)
31 2nd ON power supply part 32 3rd switch element (thyristor)
33 Power supply circuit 34 Load current value detector

Claims (7)

Two input terminals respectively connected to an AC power source and a load;
A first switch element connected between the two input terminals;
A second switch element connected in parallel with the first switch element between the two input terminals, the allowable load current of which is smaller than the allowable load current of the first switch element;
An off-power supply unit that secures DC power using an AC current flowing from the AC power source through the load when the first switch element and the second switch element are not conducted together;
An on-power supply unit that secures direct-current power using alternating current flowing from the alternating-current power supply through the load when either the first switch element or the second switch element is made conductive;
Controlled on and off of the first switch element and the second switch element based on operation information input from the outside, driven by DC power output from the off power source and on power source A two-wire load control apparatus comprising: a control unit that selects and conducts either the first switch element or the second switch element when the load is turned on.   The control unit detects a load current value flowing from the AC power source to the load when the load is on, and whether a switch element that is currently conducted is appropriate for the detected load current value. When the switch element that is currently turned on is determined to be inappropriate for the detected load current value, the switch element that is currently turned on is made non-conductive and the other switch element is made conductive. The two-wire load control device according to claim 1.   2. The two-wire according to claim 1, wherein the control unit selects one of the first switch element and the second switch element when the load is turned on based on the operation information. Type load control device. The first switch element is a relay type switch element having a switching contact that is mechanically opened and closed,
The second switch element is a semiconductor switch element that does not include a mechanically opened / closed contact,
A current transformer is connected between one of the switching contacts of the first switch element and one of the two input terminals;
The on-power supply unit is
A first on-power supply unit connected to a secondary side of the current transformer and securing a DC power using an alternating current flowing on the secondary side of the current transformer;
2. A second on power supply unit that is connected to an opening / closing unit of the second switch element and secures DC power using an AC current flowing from the AC power source through the load. The two-wire load control device according to claim 3.   A first auxiliary power supply unit that is provided between the off power supply unit or the on power supply unit and the control unit and supplies DC power to the control unit, and the first switch element is switched from a non-conductive state to a conductive state. 5. The two-wire system according to claim 1, further comprising a second auxiliary power supply unit that supplies DC power for driving the first switch element. Load control device. The control unit includes a plurality of control circuits having different drive voltages,
The off power supply unit and the on power supply unit each have a plurality of voltage systems with different drive voltages corresponding to the drive voltages of the plurality of control circuits,
The first auxiliary power supply unit is provided in a voltage system having a high drive voltage among the plurality of voltage systems, and the second auxiliary power supply unit is provided in a voltage system having a low drive voltage among the plurality of voltage systems. 6. The two-wire load control device according to claim 5, wherein the two-wire load control device is provided.   The said 1st auxiliary power supply part and the said 2nd auxiliary power supply part have an electrical storage element received with the direct-current power output from the said off power supply part or the said on power supply part, The Claim 5 or Claim 6 characterized by the above-mentioned. A two-wire load control device according to claim 1.

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