KR200256324Y1 - Step-down AC Power Control Circuit - Google Patents

Abstract

The present invention provides a step-down AC power control circuit that can reduce the number of expensive power switching elements to the maximum, and a step-down AC power control including a snubber means capable of minimizing the use of additional control circuits. The purpose is to provide a circuit.

A step-down AC power control circuit of the present invention for achieving the above object is an AC / AC power conversion circuit for directly converting an AC power source into an AC output, the AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; When the switching element is turned off, the first switching element part using the output of the first photocoupler as the control signal and the second switching element part using the output of the second photo coupler as the control signal alternately operate in parallel. Snubber means connected to said first switching element portion and said second switching element portion to one end of said bidirectional switching means and to the other end of said AC power inlet means; And a load end that can be electrically connected to the load.

Description

Step-down AC Power Control Circuit

The present invention relates to an AC power control circuit, and more particularly to a step-down AC power control circuit used in a single-phase AC-AC converter.

There is an increasing demand for power-saving single-phase AC-to-AC converters using power semiconductor devices for efficient use of energy throughout the industry. Conventionally, using a transformer for the control of the AC voltage has been used as one method. This method is widely used even now because there is no need for additional control, but in industrial applications, its use is limited due to the weight and size of the transformer. This method also causes a significant reduction in efficiency due to the structural limitations of the transformer.

Other methods include semiconductor devices, which have been used in relatively low power control applications compared to the methods using transformers. However, in recent years, with the development of power semiconductor devices, the application to the relatively large power control field is increasing. The method using the power semiconductor device has been a lot of research has been progressed to the large volume of power control in a small volume, and the application range is also increasing. In the case of the method using the power semiconductor device, if the effective configuration is premised, the power loss of the converter itself is very small and the volume can be configured very small, which is an ideal method.

Converting an AC input to an AC output using a power semiconductor device can be converted in two ways. One converts alternating current to direct current using a converter (AC / DC conversion) and then converts it back to alternating current of the desired size using an inverter (DC / AC conversion), and the other uses one converting means. Directly converts AC input to AC output. In the former case, there is an advantage in that the amount of power and supply frequency can be freely varied, but a disadvantage is that a rectifier circuit corresponding to a converter must be provided in order to convert AC into DC.

In the case of converting from AC to other levels of AC using a power semiconductor device, it is possible to achieve cost savings due to the absence of a transformer and an increase in efficiency due to little power consumed by the converter itself. In this case, various methods have been proposed, such as a cycloconverter capable of controlling frequency and power at the same time and a step-down converter controlling only power. The cycloconverter has been studied in the three-phase power field, and the step-down converter has been studied in the single-phase power field. The present invention relates to a single-phase step-down AC voltage control circuit.

1 is an embodiment of a single-phase step-down AC voltage control circuit according to the prior art, which is disclosed in Korean Patent Publication No. 171,178.

The conventional single-phase step-down AC power control circuit includes an AC input power stage 110, an output voltage controller 120 for controlling an output voltage, an LC filter 130 for filtering an output value passed through the output voltage controller, and The load stage 140 is configured, and the output voltage controller 120 requires four power switching elements.

Current power switching devices that are not signal switching devices are expensive and require additional circuitry to control the power switching devices. In addition, a switching control circuit for controlling each power switching element and a sequence for controlling each switching element are also complicated. Therefore, as the use of power switching elements increases, the production cost greatly increases. For this reason, many methods for reducing power switching devices have been studied.

On the other hand, when switching using a switching element, if the arbitrarily open the switching element is a phenomenon that the inductive load to try to flow a current continuously occurs at this time, a large voltage is applied to both ends of the switching element. If the voltage between both ends of the switching element is higher than the breakdown voltage of the switching element, the switching element may be destroyed. To prevent this, it is necessary to create a path through which the current can flow continuously. Such a circuit is generally referred to as a snubber circuit. do.

In the prior art, two unidirectional semiconductor switches are used as snubber circuits that make artificial paths using semiconductor switching elements, but in this case, driving sequences are separately configured and a separate controller is configured. If the timing of the sequence is not accurate, the entire power line will be short-circuited.

In order to solve the above problems, the present invention has an object to provide a step-down AC power control circuit that can reduce the number of expensive power switching elements to the maximum.

It is also an object of the present invention to provide a step-down AC power control circuit including snubber means capable of minimizing the use of additional control circuits.

1 is an embodiment of a single-phase step-down AC voltage control circuit according to the prior art,

2 is an overall configuration diagram of a single-phase step-down AC power control circuit according to the present invention,

3 is a detailed circuit diagram of a bidirectional switching means according to the present invention;

4 is a detailed circuit diagram of the single-phase step-down AC power control circuit according to the first embodiment of the present invention;

5 is a detailed circuit diagram of a single-phase step-down AC power control circuit according to a second embodiment of the present invention;

6 is a detailed circuit diagram of a single-phase step-down AC power control circuit according to a third embodiment of the present invention;

7 is a detailed circuit diagram of a single-phase step-down AC power control circuit according to a fourth embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

410: power stage 420: bidirectional switching means

430: snubber means 440: filtering means

450: load stage

A step-down AC power control circuit of the present invention for achieving the above object is an AC / AC power conversion circuit for directly converting an AC power source into an AC output, the AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; When the switching element is turned off, the first switching element part using the output of the first photocoupler as the control signal and the second switching element part using the output of the second photo coupler as the control signal alternately operate in parallel. Snubber means connected to said first switching element portion and said second switching element portion to one end of said bidirectional switching means and to the other end of said AC power inlet means; And a load end that can be electrically connected to the load.

Preferably, the present invention is characterized in that the reactor further comprises a LC filtering means connected in series with the bidirectional switching means in order to filter the output from the bidirectional switching means, the capacitor in parallel to the load end.

Preferably, the snubber means of the present invention, two photodiodes of the anti-parallel connection is connected to the AC power inlet means in parallel to each phototransistor to form a photocoupler and the two photodiodes Alternatingly turn-on according to the phase of the power supply voltage, and using the output signal of the phototransistor as a control signal to turn on the first switching element portion or the second switching element portion.

In addition, the step-down AC power control circuit of another design of the present invention is an AC / AC power conversion circuit for directly converting an AC power source into an AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; When the first phototransistor of the first photocoupler and the second phototransistor of the second photocoupler are alternately turned on and the switching element is turned off according to the phase of the applied power voltage, the first phototransistor is connected in series with the first phototransistor. In order for the first diode to be turned on or the second diode connected in series with the second phototransistor to be turned on, one side of the first phototransistor and the second phototransistor connected in parallel to the one end of the bidirectional switching means, A snubber means connected to the other end of the AC power inlet means; And a load end that can be electrically connected to the load.

Preferably, another design of the present application is characterized in that the reactor further comprises a LC filtering means connected in series with the bidirectional switching means and the capacitor connected in parallel with the load stage to filter the output from the bidirectional switching means. do.

Preferably, the snubber means of another design of the present invention, two photodiodes of the anti-parallel connection is connected to the AC power supply means in parallel to each phototransistor applied to form a photocoupler and the two photodiodes Alternately turn on according to the phase of the power supply voltage.

In addition, the step-down AC power control circuit of another design of the present invention is an AC / AC power conversion circuit for directly converting AC power to AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; When the first phototransistor of the first photocoupler and the second phototransistor of the second photocoupler are alternately turned on and the switching element is turned off according to the phase of the applied power supply voltage, the parallel connection with the first phototransistor is performed. In order for the first diode to be turned on or the second diode connected in anti-parallel with the second phototransistor to be turned on, one end of the first phototransistor and the second phototransistor connected in series are one end of the bidirectional switching means. Snubber means connected to the other end of the AC power supply means; And a load end that can be electrically connected to the load.

Preferably, another design of the present application is characterized in that the reactor further comprises an LC filtering means connected in series with the bidirectional switching means and a capacitor connected in parallel with the load stage to filter the output from the bidirectional switching means. It is done.

Preferably, the snubber means of another design of the present invention, each of the two photodiodes of the anti-parallel connection is connected to the AC power supply means in parallel to form each phototransistor to form the two photodiodes and the port coupler And alternately turn on in accordance with the phase of the applied power supply voltage.

In addition, the step-down AC power control circuit of another design of the present invention is an AC / AC power conversion circuit for directly converting AC power to AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; In order for the first phototransistor of the first photocoupler and the second phototransistor of the second photocoupler to be alternately turned on according to the phase of the applied power voltage, the first phototransistor and the second phototransistor connected in parallel are Snubber means connected to one end of the bidirectional switching means, the other end of the AC power supply means; And a load end that can be electrically connected to the load.

Preferably, another design of the present application is characterized in that the reactor further comprises an LC filtering means connected in series with the bidirectional switching means and a capacitor connected in parallel with the load stage to filter the output from the bidirectional switching means. It is done.

Preferably, the snubber means of another design of the present invention, each of the phototransistors in which two photodiodes in parallel and parallel connection are connected in parallel to the AC power inlet means to form the two photodiodes and photocouplers And alternately turn on in accordance with the phase of the applied power supply voltage.

Preferably, the switching element in the bidirectional switching means of the present invention is characterized in that it is possible to control the interruption of the current irrespective of the direction of the voltage across both ends of the switching element.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can more easily implement the present invention.

2 is an overall configuration diagram of a single-phase step-down AC power control circuit according to the present invention.

The single-phase step-down AC power control circuit of the present invention prevents an overvoltage occurring at both ends of the bidirectional switching means due to the interruption of the AC power inlet means 210, the bidirectional switching means 220 for controlling the AC power, and the bidirectional switching means. It consists of a snubber means 230, an LC filtering means 240, and a load stage 250. Hereinafter, the components will be described in more detail.

3 is a detailed circuit diagram of the bidirectional switching means 220 according to the present invention. In the bidirectional switching means 220, one switching element is connected between four bridge diodes. That is, the diode D1 is connected between the first node and the fourth node, the diode D3 is connected between the fourth node and the second node, the diode D2 is connected between the first node and the third node, and the third node is connected. The diode D4 is connected between the second node and the second node, and the switching element Q1 is connected between the fourth node and the third node. This circuit works as follows.

If the first node is positive and the second node is negative according to the polarity of the AC power supply voltage, the current flows in the direction of the first node-> D1-> Q1-> D4-> second node, and the second node is positive. If the second node is negative, the current flows in the direction of the second node-> D3-> Q1-> D2-> first node. In other words, current always flows through Q1 regardless of the polarity of the input voltage. Therefore, the amount of current flowing to the load can be controlled by adjusting the turn-on time of the switching element Q1. The switching element that can be used at this time is for power that can arbitrarily turn on / off the current flowing in the load irrespective of the polarity of the voltage across both ends of the switching element such as field effect transistor (FET), bipolar transistor (BJT), IGBT, etc. As long as it is a semiconductor element, it is possible and it does not need to be limited to any.

4 is a detailed circuit diagram of the single-phase step-down AC power control circuit according to the first embodiment of the present invention, and the snubber means 430 of the present invention will be described.

The snubber means 430 according to the present invention does not require a separate control circuit for generating a control signal by appropriately using two photocouplers PC1 and PC2 composed of a photodiode PD and a phototransistor PT. The operation of the snubber means 430 is as follows.

First, when the first node is positive potential, the fifth node is negative potential, and Q1 is ON, the first node in the direction of load 450-> D1-> Q1-> D4-> L1-> C1-> 5th node Alternatively, current flows in the order of the first node-> D1-> Q1-> D4-> L1-> load-> 5th node, and power is supplied to the photodiode PD2 through R2 to conduct the photodiode PD2. As a result, the phototransistor PT2 becomes conductive. At this time, when Q1 changes from ON to OFF, the current line is opened and the second node is suddenly switched to negative potential. At this time, the current flowing through the resistor R4 and the phototransistor PT2 turns Q3 on, thereby forming a current path through Q3-> D6-> L1-> load or Q3-> D6-> L1-> C1. The element Q1 is protected. This operation is automatically performed when Q1 performs the ON-OFF operation unless the potentials of the first node and the fifth node are changed. At this time, since the photocoupler PC1 is in an open state, the transistor of Q2 also remains open.

Next, when the fifth node has the positive potential, the first node has the negative potential, and Q1 is in the ON state, the fifth node-> load-> L1-> D3-> Q1-> D2-> first node toward the load 450 direction. Alternatively, current flows in the order of the fifth node-> C1-> L1-> D3-> Q1-> D2-> first node, and power is supplied to the photodiode PD1 through R1 to conduct the photodiode PD1. As a result, the phototransistor PT1 becomes conductive. At this time, when Q1 is changed from ON to OFF, the current line is opened and the second node is rapidly switched to the positive potential. At this time, the current flowing through the resistor R3 and the phototransistor PT1 turns on Q2, thereby forming a current path through Q2-> D5-> C1-> L1 or Q2-> D5-> load-> L1. (Q1) will be protected. This operation is automatically operated when the switching element Q1 performs the ON-OFF operation unless the potentials of the first node and the fifth node are changed. At this time, the port coupler PC2 is in an open state, so Q3 also remains open. Here, the resistors R1, R2, R3 and R4 operate as protective resistors.

In addition, the switching element used in the snubber means of the present invention is a unidirectional switching element such as a bipolar junction transistor (BJT), an IGBT, a field effect transistor (FET), etc., which may or may not be basically equipped with a protection diode. If there is no protection diode, it can be connected in parallel with the unidirectional switching element. In addition, R5 and R6 are determined according to the type of switching element, and are required in the case of a voltage driven switching element such as a field effect transistor (FET), and a current driving type such as a bipolar junction transistor (BJT). It is unnecessary in the case of a switching element.

On the other hand, the switching speed of the switching element used in the snubber means 430 of the present invention does not have to be relatively fast compared to the switching speed of the switching element used in the bidirectional switching means 420 of the present invention, thus reducing the cost. Can bring

5 is a detailed circuit diagram of the single-phase step-down AC power control circuit according to the second embodiment of the present invention. The configuration is the same as that of the first embodiment of the present invention, and only the detailed configuration of the snubber circuit 530 is different. The operation of the snubber circuit 530 will be described below.

First, when the first node has a positive potential, the fifth node has a negative potential, and Q1 is in an ON state, the current flowing in the load 550 direction is first node-> D1-> Q1-> D4-> L1-> C1-> The fifth node or the first node-> D1-> Q1-> D4-> L1-> load-> 5th node flows in order, and power is supplied to the photodiode PD4 through R2 to conduct photodiode PD4. Thus, phototransistor PT4 is conducted. However, since node 2 has a positive potential compared to node 5, diode D6 has a reverse voltage, and thus no current flows to diode D6.

When Q1 changes from ON to OFF, the current line is opened and the second node suddenly switches to negative potential due to the characteristics of reactor L1. At this time, since the phototransistor PT4 is conductive, a current path through PT4-> D6-> L1-> load or PT4-> D6-> L1-> C1 is formed to protect the switching element Q1. This operation is automatically performed when Q1 performs the ON-OFF operation unless the potentials of the first node and the fifth node are changed. At this time, the photocoupler PC3 remains open.

On the other hand, if the fifth node has a positive potential, the first node has a negative potential, and Q1 is in an ON state, the fifth node-> load-> L1-> D3-> Q1-> D2-> first node toward the load 550 direction. Alternatively, current flows in the order of the fifth node-> C1-> L1-> D3-> Q1-> D2-> first node, and power is supplied to the photodiode PD3 through R1 to conduct the photodiode PD3, As a result, the phototransistor PT2 becomes conductive. However, since node 5 has a positive potential compared to node 2, diode D5 has a reverse voltage, and thus no current flows to diode D5.

When Q1 is changed from ON to OFF, the current line is opened and the second node is rapidly switched to the positive potential by the characteristic of reactor L1. At this time, since the phototransistor PT4 is conductive, a current path through PT3-> D5-> C1-> L1 or PT3-> D5-> load-> L1 is formed to protect the switching element Q1. This operation is automatically operated when the switching element Q1 performs the ON-OFF operation unless the potentials of the first node and the fifth node are changed. At this time, the port coupler PC4 remains open.

Such a configuration becomes possible according to the tendency of the large capacity of a photocoupler.

FIG. 6 is a detailed circuit diagram of the single-phase step-down AC power control circuit according to the third embodiment of the present invention. The configuration is the same as that of the second embodiment of the present invention, and only the detailed configuration of the snubber circuit 530 is different.

That is, in the snubber circuit 530 of the second embodiment, the phototransistor PT3 and the diode D5 and the phototransistor PT4 and the diode D6 are connected in series, respectively, but the snubber circuit 630 of the third embodiment has the phototransistor PT5 and the diode. The difference is that D6 and phototransistor PT6 and diode D5 are each connected in parallel.

However, as the snubber circuit 530 of the second embodiment operates in a pair of phototransistor PT3 and diode D5 and the phototransistor PT4 and diode D6 respectively, the snubber circuit 630 of the third embodiment uses a phototransistor PT5. And diode D5, phototransistor PT6 and diode D6 operate in pairs, respectively, and the operation of the remaining circuit of the third embodiment is completely consistent with that of the second embodiment. On the other hand, the phototransistor of the photocoupler applied to the first to third embodiments of the present invention may be a bidirectional device.

In general, the term photocoupler refers to an optically electrical coupling. However, this is not the only limitation here. There are a myriad of electrical couplers used in industrial sites, so I can't list them all. That is, it can be divided into coupler by electronic operation and coupler by optical operation according to the control method, and it is composed of phototransistor according to the type of switch, photothyristor (SCR), phototriac, photoelectric field effect transistor (FET). The current can be divided into two directions according to the current flow type, and one can be divided into one direction.

Enumerating all the electrical couplers in this way is not only a hard work but also a waste of the ground, so all of these are collectively referred to as photocouplers. The lead means, which turns the switch on and off, is called a photodiode, and the means for passing a current is collectively called a photo transistor.

FIG. 7 is a detailed circuit diagram of the single-phase step-down AC power control circuit according to the fourth embodiment of the present invention, in which diodes D5 and D6 are omitted, which is possible if the photo coupler can pass current in only one direction. The circuit operation of the fourth embodiment is the same as that of the second embodiment, and therefore will be omitted.

Herein, the present invention can be applied to lighting control of street lamps such as sodium lamps, mercury lamps, lighting control of domestic and industrial bulbs such as fluorescent lamps, incandescent lamps, and single-phase AC motors.

On the other hand, the switching method of the switching element of the bidirectional switching means 420 in order to adjust the power required at the load stage is generally known PWM method for adjusting the pulse width or PFM method for adjusting the frequency, where The PWM and PFM methods have the same effect by adjusting the filter coefficients.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

As described above, the present invention can control the amount of power supplied to the load by operating only one switching element, and can reduce the production cost by presenting a snubber circuit that is extremely simple but does not cause a malfunction.

Claims (13)

In the AC / AC power conversion circuit which directly converts AC power into AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; When the switching element is turned off, the first switching element part using the output of the first photocoupler as the control signal and the second switching element part using the output of the second photo coupler as the control signal alternately operate in parallel. Snubber means connected to said first switching element portion and said second switching element portion to one end of said bidirectional switching means and to the other end of said AC power inlet means; And Load stages that can be electrically connected to the load Step-down AC power control circuit comprising a. The method of claim 1, A reactor is connected in series with the bidirectional switching means for filtering the output from the bidirectional switching means, and the capacitor is LC filtering means connected in parallel with the load stage. Step-down AC power control circuit further comprising. The snubber means according to claim 1 or 2, Two photodiodes connected in anti-parallel are connected in parallel to the AC power supply means to turn on each phototransistor which forms the two photodiodes and the photocoupler alternately according to the phase of an applied power supply voltage, and the photo A step-down AC power control circuit comprising turning on the first switching element portion or the second switching element portion using an output signal of a transistor as a control signal. In the AC / AC power conversion circuit which directly converts AC power into AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; The first phototransistor of the first photocoupler and the second phototransistor of the second photocoupler are alternately turned on according to the phase of the applied power supply voltage, and are connected in series with the first phototransistor when the switching element is turned off. In order for the first diode to be turned on or the second diode connected in series with the second phototransistor to be turned on, one side of the first phototransistor and the second phototransistor connected in parallel to the one end of the bidirectional switching means, A snubber means connected to the other end of the AC power inlet means; And Load stages that can be electrically connected to the load Step-down AC power control circuit comprising a. The method of claim 4, wherein A reactor is connected in series with the bidirectional switching means for filtering the output from the bidirectional switching means, and the capacitor is LC filtering means connected in parallel with the load stage. Step-down AC power control circuit further comprising. The method according to claim 4 or 5, wherein the snubber means, Two photodiodes connected in parallel and parallel are connected to the AC power supply means in parallel to turn on each phototransistor forming the two photodiodes and the port coupler alternately according to the phase of an applied power supply voltage. Step-down AC power control circuit. In the AC / AC power conversion circuit which directly converts AC power into AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; When the first phototransistor of the first photocoupler and the second phototransistor of the second photocoupler are alternately turned on and the switching element is turned off according to the phase of the applied power supply voltage, the parallel connection with the first phototransistor is performed. In order for the first diode to be turned on or the second diode connected in anti-parallel with the second phototransistor to be turned on, one end of the first phototransistor and the second phototransistor connected in series are one end of the bidirectional switching means. Snubber means connected to the other end of the AC power supply means; And Load stages that can be electrically connected to the load Step-down AC power control circuit comprising a. The method of claim 7, wherein A reactor is connected in series with the bidirectional switching means for filtering the output from the bidirectional switching means, and the capacitor is LC filtering means connected in parallel with the load stage. Step-down AC power control circuit further comprising. The method according to claim 7 or 8, wherein the snubber means, Two photodiodes connected in parallel and parallel are connected to the AC power supply means in parallel to turn on each phototransistor forming the two photodiodes and the port coupler alternately according to the phase of an applied power supply voltage. Step-down AC power control circuit. In the AC / AC power conversion circuit which directly converts AC power into AC output, AC power supply means having one end and the other end; A bidirectional switching means comprising a bridge diode and one switching element so as to allow a current to pass regardless of a phase inversion of the AC power, one end connected to the AC power inlet means and the other end connected to the load side-wherein the switching element Is connected between the bridge diodes; In order for the first phototransistor of the first photocoupler and the second phototransistor of the second photocoupler to be alternately turned on according to the phase of the applied power voltage, the first phototransistor and the second phototransistor connected in parallel are Snubber means connected to one end of the bidirectional switching means, the other end of the AC power supply means; And Load stages that can be electrically connected to the load Step-down AC power control circuit comprising a. The method of claim 10, A reactor is connected in series with the bidirectional switching means for filtering the output from the bidirectional switching means, and the capacitor is LC filtering means connected in parallel with the load stage. Step-down AC power control circuit further comprising. The method according to claim 10 or 11, wherein the snubber means, Two photodiodes connected in parallel and parallel are connected to the AC power supply means in parallel to turn on each phototransistor forming the two photodiodes and the photocoupler alternately according to the phase of an applied power supply voltage. Step-down AC power control circuit. The switching element according to any one of claims 1 to 12, wherein the switching element in the bidirectional switching means includes: Step-down AC power control circuit, characterized in that it is possible to control the interruption of the current irrespective of the direction of the voltage across the switching element.