JP5330548B2 - Overvoltage protection circuit for each switch power cycle - Google Patents

Abstract

A cycle-by-cycle over voltage protection circuit (1) for a switching power supply includes a thyristor (SCR), a zener diode (TVS), a first resistor (R1), a second resistor (R2), a second diode (D2) and a second capacitor (C2). The anode of the thyristor (SCR) is connected to an alternating current input terminal (ACIT) and the cathode of the thyristor (SCR) is connected to a load terminal (LDT). The cathode of the zener diode (TVS) is connected to the gate of the thyristor (SCR) and the anode of the zener diode (TVS) is connected to the first resistor (R1) and the second resistor (R2) connected to each other in parallel. The first resistor (R1) is directly connected to the alternating current input terminal (ACIT) and the second resistor is connected to the alternating current input terminal (ACIT) through the second diode (D2) of which the connection direction is converse to that of the zener diode (TVS). The second capacitor (C2) is connected between the cathode of the thyristor (SCR) and the cathode of the zener diode (TVS). A first capacitor (C1) is connected between the load terminal (LDT) and a load ground terminal (LDGT).

Description

  The present invention relates to an overvoltage protection technique, and more particularly to an overvoltage protection circuit for each switch power supply cycle.

  The various environmental conditions of the power supply are relatively complex, and if not good, even if the grid voltage is unstable and 220 VAC and 380 VAC are difficult to determine, too much voltage will be input from the power input end, so in the electrical equipment Internal parts / members including the energy storage capacitor in the switch power supply are damaged by receiving a voltage that is too high, which adversely affects the normal operation of the entire appliance. In such a case, in order to protect the electrical equipment, a method of adding an overvoltage protection circuit to the power input terminal is generally adopted. There are usually several protection methods:

  First, a positive temperature coefficient thermistor fuse PTCC and a metal oxide pressure-sensitive varistor MOV are used to perform coupling protection. As shown in FIG. 1, when the input exceeds a predetermined value from the AV input terminal, the resistance value of the pressure-sensitive varistor is rapidly lowered to form a high power circuit, and the PTCC has a relatively high current. Is switched to a high impedance state rather than being rapidly heated to achieve the purpose of protecting the subsequent circuits of the power supply by limiting the current passed through the circuit to be very low. However, the disadvantage is that the pressure-sensitive varistor has a relatively short service life, a slow reaction time, and once protection is started, the power should be turned off so that the PTCC can cool down and return to a low impedance state. After that, it is finally mentioned that the operation is continuing.

  Method 2 and method 2 are improvements of method 1 in which a constant voltage diode is used instead of a pressure sensitive varistor. As shown in FIG. 2, the constant voltage diode overcomes the drawbacks of the pressure-sensitive varistor, the reaction time is very fast, the service life is long, the matching of the limiting voltage is relatively high, and the input from the AV input terminal is relatively high When the voltage exceeds the limit voltage of the constant voltage diode, the constant voltage diode is destroyed, its impedance is immediately reduced, and the voltage is limited to the limit voltage of the constant voltage diode, forming a high power circuit. PTCC protects subsequent circuits of the power supply by limiting the current passed through the circuit to be very low by switching to a high impedance state rather than being heated rapidly when a relatively high current is passed. Reach the purpose. However, the disadvantage is that the protection should be started once and the power supply should be turned off, and after PTCC has cooled down and returned to the low impedance state, the operation is finally continued normally.

  Third, it is an overvoltage protection method that uses a thyristor. As shown in FIG. 3, when the AV input voltage rises to a predetermined voltage of the protection circuit (the resistance value of R1 and R2 can be changed, the predetermined voltage can be changed). ), The trigger diode DS is turned on, the thyristor is turned on, the current is passed through the PTCC, the thyristor current limiting resistor R3, the thyristor forms a high power circuit, and the PTCC is passed through a relatively high current. The purpose of protecting the subsequent circuits of the power supply is achieved by switching to a high impedance state rather than rapidly generating heat and limiting the current passed through the circuit to be very low. However, the disadvantage is that protection with PTCC should be started once and the power supply should be cut off, and after PTCC has cooled down and returned to a low impedance state, the operation is finally continued normally. It is done.

  No.4, a voltage limit protection method that uses thyristors. The principle of the method is as shown in FIG. 4, and the control circuit sends an appropriate delayed trigger pulse via the comparison and arithmetic circuit according to the level of the AV input voltage. Outputs to control the thyristor conduction time so that the voltage of the subsequent circuit of the switch power supply does not exceed the maximum working voltage. Such a protection method is good, but it is not appropriate to use it for a low-power switch power supply because the control circuit is very complicated and the realization cost is high.

  5. Adopting relay overvoltage protection, the AV input voltage rises and the DC voltage after rectification also increases, and when the DC voltage becomes higher due to the limit voltage of the constant voltage diode, the constant voltage diode is destroyed Then, the transistor Q1 is turned on, the relay is activated, the normally closed contact is turned OFF, the voltage of the subsequent power supply circuit is cut off, and the purpose of protecting the input overvoltage is achieved. The method was simple and reliable, but the disadvantage is that when the voltage flicker is relatively large, the relay sometimes becomes active, affecting the continuous and stable supply of power, In order to introduce a relay in the protection circuit, a power source for operating the relay should be provided separately, which is complicated and large in volume and is not appropriate for use in a low power switch power source. It is done.

  Accordingly, an object of the present invention is to provide a power supply that directly samples the power grid voltage according to the thyristor AC cutting principle and automatically changes the conduction time of the thyristor according to the level of the AC input voltage in order to solve the problems of the existing technology. An overvoltage protection circuit for a switch is provided.

  In order to solve the technical problem, the present invention is constituted by the following technical means.

An overvoltage protection circuit for each switch power cycle, wherein one overvoltage protection circuit 1 is connected between an AC input and a load. The overvoltage protection circuit 1 includes a thyristor, a constant voltage diode, a first resistor, The thyristor has an anode connected to an AC input terminal, a cathode connected to a load terminal, and a cathode of the constant voltage diode and a gate electrode of the thyristor. The anode of the constant voltage diode is connected to the first resistor and the second resistor that are parallel to each other, the first resistor is directly connected to the AC input terminal, and the second resistor is installed in the opposite direction to the constant voltage diode. that is connected to the AC input end by being connected to the second diode, the second capacitor is connected between the cathode of the cathode and a low voltage diode thyristor, the load end Is first condenser connected between the load ground end, further, between the cathode and the load end of the thyristor, the first diode is installed to be connected to a thyristor in the same direction, and the anode of the first diode and the common ground terminal during, Ru third resistor is connected.

  With regard to said means, preferably further comprising a third diode, said third diode being connected in series with a third resistor, its cathode being connected to the third resistor and its anode being connected to the common earth terminal.

An overvoltage protection circuit for each switch power cycle, wherein one overvoltage protection circuit 1 is connected between an AC input and a load. The overvoltage protection circuit 1 includes a first thyristor, a first constant voltage diode, and a first A resistor, a second resistor, a first diode, a first capacitor, and a second capacitor, the anode of the first thyristor is connected to the AC input terminal, the cathode is connected to the load terminal, and the first The cathode of the constant voltage diode and the gate electrode of the first thyristor are connected, the anode of the first constant voltage diode is connected to the first resistor and the second resistor, respectively, which are parallel to each other, and the first resistor is directly connected to the AC input terminal. The second capacitor is connected to the AC input terminal by being connected to the first diode installed in the opposite direction to the first constant voltage diode, and the second capacitor is connected to the shadow of the first thyristor. And a cathode of the first constant voltage diode, a first capacitor is connected between the load end and the load ground end, and the overvoltage protection circuit 1 further includes a second diode and a third diode. The anode of the second diode is connected to the common ground end, the cathode is connected to the load end, the third diode is connected to the connection line between the common ground end and the load ground end, and the anode of the third diode is the first is connected to the cathode of the capacitor, the cathode of the third diode is connected to the anode of the second diode, between the AC input and the load ground, the overvoltage protection circuit 2 is connected, the overvoltage protection circuit 2, a second and thyristor, a second constant-voltage diode, and a third resistor, a fourth resistor, a third capacitor, a fourth diode, an anode of the second thyristor is connected to the load ground end, Cathode is connected to the AC input ends, the cathode of the second zener diode is connected to the gate electrode of the second thyristor, a third resistor and a fourth resistor anode of the second zener diode are parallel to each other Connected, the third resistor is directly connected to the load ground terminal, the fourth resistor is connected to the fourth diode connected in the opposite direction to the second constant voltage diode, and is connected to the load ground terminal, and the third capacitor is Connected between the cathode of the second thyristor and the cathode of the second constant voltage diode.

  Therefore, the present invention directly samples the power grid voltage according to the thyristor AC cutting principle, and automatically changes the conduction time of the thyristor according to the level of the AC input voltage to achieve cycle-by-cycle control over the AC input power source. Therefore, it avoids the disadvantage of slow reaction time, and can automatically correct in real time against the flicker of the power grid voltage, achieving overvoltage protection of the subsequent circuit of the power supply.

It is a 1st circuit diagram of existing technology. It is a 2nd circuit diagram of existing technology. It is a 3rd circuit diagram of existing technology. It is a 4th circuit diagram of existing technology. It is a 5th circuit diagram of existing technology. It is a basic circuit diagram of single phase half-wave overvoltage protection of the present invention. It is a development circuit diagram of the single phase half wave overvoltage protection of the present invention. It is a basic circuit diagram of single phase full wave overvoltage protection of the present invention. It is a development circuit diagram of the single phase full wave overvoltage protection of the present invention. It is waveform explanatory drawing of the single phase half-wave overvoltage protection basic circuit of this invention. It is voltage waveform explanatory drawing of the single phase half-wave overvoltage protection expansion circuit A point of this invention.

  Hereinafter, the technical means of the present invention will be described in more detail with reference to the drawings.

[Example 1]
The single-phase half-wave overvoltage protection basic circuit shown in FIG. 6 is installed between an AC input and a load, and includes an overvoltage protection circuit 1, a diode D1, a resistor R3, and a capacitor C1. The configuration of the protection basic circuit includes one thyristor SCR, one constant voltage diode TVS, and one resistor R3. The anode of the thyristor SCR is connected to the AC input terminal, and the cathode is connected to the thyristor SCR. The resistor R1 is connected to the load terminal by being connected to the diode D1 installed in the same direction, connected to the cathode of the constant voltage diode TVS and the gate electrode of the thyristor SCR, and the anode of the constant voltage diode TVS is parallel to each other. And resistor R2, resistor R1 is directly connected to the AC input terminal, and resistor R2 is in the opposite direction to constant voltage diode TVS. The capacitor C2 is connected between the cathode of the thyristor SCR and the cathode of the constant voltage diode TVS, and the resistor R3 is connected to the anode of the diode D1 and the AC input. The capacitor C1 is connected between the load input terminal and the load ground terminal. The thyristor SCR, the diode D1, and the capacitor C1 constitute a current input main circuit, and the resistor R1, the constant voltage diode TVS, the capacitor C2, and the resistor R3 constitute a control circuit 1 that generates a trigger pulse for the thyristor, and the diode D2, the resistor R2, the constant voltage diode TVS, the capacitor C2, and the resistor R3 constitute a control circuit 2 that generates a trigger pulse for the thyristor.

The operating principle of this circuit is that when the AC input enters the initial phase of the positive half cycle, the A terminal as the pulse trigger terminal of the thyristor SCR assumes a low level state, and the A point voltage is as shown in FIG. When the thyristor SCR is cut off, the voltage of C is higher than the point B, the diode D1 exhibits a reverse cut-off state, and the storage capacitor C1 cannot be discharged from the reverse direction to the input circuit. As the positive half-cycle voltage gradually increases, the current charges the capacitor C2 in the positive direction via the control circuit 1, that is, the resistor R1, the constant voltage diode TVS, and the resistor R3. At that time, the constant voltage diode TVS is in the positive direction. becomes conductive, the voltage gradually rises in the positive half cycle due to the AC input voltage at point a is also just as gradually increases, the voltage at point a exceeds the gate electrode trigger voltage V _SCR thyristor At this time, the thyristor SCR becomes conductive and the charging of the capacitor C2 is finished, and the forward charging time for the capacitor C2 is referred to as T _{C2 +} (as shown in FIG. 10). After the thyristor SCR becomes conductive, the voltage at the point A gradually rises, and the voltage at the point B becomes the voltage V _{C1 at the} C point (voltage at the end of the voltage C1) +0.7 V (positive voltage drop of the diode D1). When D1 is exceeded, D1 becomes conductive, the current is charged into the capacitor C1 through the main circuit, the voltage V _{C1 at the} point C gradually rises, and the voltage of the positive half cycle gradually falls. When the voltage at the point B is gradually lowered and the voltage at the point B becomes lower than the voltage V _C1 +0.7 V at the point C, the D1 is cut off, the charging for the capacitor C1 is completed, and the charging time for the capacitor C1 is completed. Is referred to as T _C1 (as shown in FIG. 10). Since the resistance value of the resistor R3 is very high, the current flowing through the thyristor SCR is smaller than the maintenance current of the thyristor, the thyristor SCR is cut off, the current output main circuit is disconnected, and the conduction time of the thyristor SCR is T _SCR (As shown in FIG. 10). At that time, the current that flows through the thyristor SCR in real time is larger than the sustain current, and the thyristor SCR becomes conductive. However, when the input voltage approaches to zero, the thyristor SCR is automatically turned off, and the current output Disconnect the main circuit.

Since the charging time of capacitor C1 _{T C1} and conduction time of the thyristor SCR and _{T SCR} is turned direct proportion, the longer the conduction time of the thyristor SCR, the voltage _{V C1} is higher in the condenser C1. Conduction of thyristor SCR is gated electrode, the gate electrode reaches the trigger voltage V _SCR, thyristor SCR is turned on. The longer the time T _{C2 + for} the voltage V _{C2 at} point A to reach V _SCR , the shorter the conduction time T _SCR of the thyristor SCR and the voltage at the storage capacitor C1 also lower, so the charging time T _{C2 + in the} positive direction with respect to _C2 If well controlled, the voltage V _{C1 at the} capacitor C1 can be kept within the safe use range, thereby achieving the purpose of protecting the load circuit. This is all conditional on the AC input voltage being stable. If the AC input voltage suddenly rises, the charging current in the control circuit 1 increases with time, the time T _{C2 +} for reaching the gate trigger voltage V _SCR is shortened, the conduction time T _SCR of the thyristor _SCR is extended, and the capacitor Since the charging time T C1 for _C1 is extended and the voltage V _C1 at the capacitor C1 is correspondingly increased, the control circuit 1 solves the control over the charging time T _{C1 at the} capacitor C1 by further cooperation with the control circuit 2 Should do.

In the positive half cycle of the AC input, the diode D2 in the control circuit 2 is turned off in the reverse direction, the control circuit 2 is useless, and the negative voltage is relatively small just after entering the negative half cycle. It enters a high resistance state with no conduction, has a slight leakage current in the control circuit, has very little influence on the voltage at the point A, and the voltage at the point A is basically unchanged. As the negative voltage increases, when the negative voltage exceeds the limit voltage V _TVS of the constant voltage diode TVS, the resistance of the constant voltage diode TVS is immediately reduced, and the voltage is limited to the limit voltage of the constant voltage diode TVS. In circuit 2, a reverse charging circuit for capacitor C2 is formed to change the voltage at point A from a positive voltage to a negative voltage, and the negative voltage at point A is referred to as V _C2− . The charging time for capacitor C2 is referred to as T _C2 (as shown in FIG. 10). If by the AC input voltage is increased (AC input negative voltage is increased), reverse charging current is also increased, since the breaking time of the constant voltage diode TVS is incremented when co, charging time T _C2- increases for capacitors C2 ing. By extending the charging time of C2 and increasing the charging current, a higher negative voltage V _C2− was formed at point A. The _level of the negative voltage V _C2- formed at the point A is such that the circuit 1 in the positive half cycle of the AC input affects the positive charging time for the capacitor C2, and the higher the negative voltage V _{C2-at the} point A, C2 in the forward charge time is a time TC2 ₊ for the thyristor SCR to reach the conduction gate limit voltage V _SCR is increased, thereby shortening the conduction time T _SCR of the thyristor SCR, and therefore for the capacitor C1. The charging time T _C1 is reduced and the voltage V _C1 at the capacitor C1 is also lowered to achieve the protection purpose for the load.

Conversely, it a negative voltage of the AC input is reduced, the reverse charging current is reduced, since the time that is breakdown of the constant voltage diode TVS is delayed, reverse charging time T _C2- shortening for capacitor C2 The capacitor C2 resulted in the formation of a relatively low negative voltage V _C2 at point A due to the shortened charging time and the reduced charging current. Will be eventually reducing the time capacitor C2 is thyristor SCR in case of positive charging is reached to trigger the conduction gate limit voltage V _SCR, thereby, increase the charging time T _C1 for capacitor C1, the capacitor C1 The voltage V _C1 was also raised to ensure the stability of the voltage at the capacitor C1.

  In general, the voltage values in the positive and negative half cycles of the AC input voltage are the same, and the resistor R1 in the control circuit 1 still plays a role in the negative half cycle of the AC input, so that the reverse charging of the capacitor C2 is performed. The current is greater than the positive charge current for capacitor C2 in the positive half cycle of the AC input. When the member parameters of the circuit 1 and the circuit 2 are appropriately selected and the AC input voltage exceeds a predetermined safety voltage (for example,> 320 AC), the voltage at the point A is the half cycle of the AC input. Since the gate limit voltage can be reached, the thyristor cannot be conducted, and the AC input circuit is disconnected to protect the safety of the load.

  The control circuit 1 and the control circuit 2 realize control for each radio wave, automatic cutting and voltage limitation for the AC input power supply. In response to a sudden voltage increase, conduction is made within at most one half cycle, and with only one half cycle voltage, the capacitor C1 and the load are usually completely consumed, and the circuit members are damaged. As a result, the safety of the load was completely guaranteed.

[Example 2]
As shown in FIG. 7, one single-phase half-wave overvoltage protection deployment circuit was provided. The circuit configuration basically coincides with the configuration of the single-phase half-wave overvoltage protection basic circuit of the first embodiment, and further includes one diode D3. The cathode of the diode D3 is connected in series with the resistor R3, and its anode Is connected to the common ground end. Compared with the first embodiment, the circuit 1 charges the capacitor C2 in the positive direction only when the positive half cycle of the AC input is at the start stage and the voltage of the positive half cycle of the input is higher than the voltage at the capacitor C1. Starting and delaying the forward charging time for the capacitor C2, the conduction time of the thyristor SCR is also shortened, and when the charging time for the capacitor C1 is decreased, the voltage of the capacitor C1 is also lowered to play a role of load protection. Resistor R3 cannot work due to reverse blocking of diode D3. When the AC input enters the negative half cycle, the diode D3 is in the forward direction, and the reverse charging state of the circuit 2 with respect to the capacitor C2 is the same as that of the first embodiment.

Example 3
As shown in FIG. 8, the present invention provided one single-phase full-wave overvoltage protection basic circuit. The circuit configuration is based on the circuit of the second embodiment, in which an overvoltage protection circuit 2 is connected between an AC input and a load, and the single-phase overvoltage protection basic circuit 2 includes a thyristor SCR. 1 and the constant voltage diode TVS. 1, resistor R1.1, resistor R2.1, resistor R3.1, diode D1.1, diode D2.1, diode D3.1, and capacitor C2.1, the thyristor SCR. 1 is connected to the common earth terminal, and its cathode is connected to the thyristor SCR. 1 is connected to the load end by being connected to a diode D1.1 in series with the same direction as that of the constant voltage diode TVS. 1 anode and thyristor SCR. 1 is connected to the gate electrode of the constant voltage diode TVS. 1 are connected to resistors R1.1 and R2.1, which are parallel to each other, the resistor R1.1 is directly connected to the common ground terminal, and the resistor R2.1 is connected to the constant voltage diode TVS. 1 is connected to the common earth end by connecting to the diode D2.1 installed in the same direction as the capacitor 1, and the capacitor C2.1 is connected to the thyristor SCR. 1 cathode and constant voltage diode TVS. The resistor R3.1 and the diode D3.1 are connected in series between the anode of the diode D1.1 and the AC input terminal, and the cathode of the diode D3.1 is connected to the diode D3. 1 and its anode is connected to the AC input. The operating principle is the same as in the first embodiment. In the first and second embodiments, the capacitor C1 is charged only when the AC input enters only the positive half cycle, and the capacitor C1 can be charged in both the positive and negative half cycles of the AC input in this embodiment. The stability of the voltage in the capacitor C1 was improved.

Example 4
As shown in FIG. 9, the present invention further provides one single-phase full-wave overvoltage protection deployment circuit. The circuit includes an overvoltage protection 1, and an overvoltage protection circuit 3 is further connected between the AC input terminal and the load ground terminal, and the overvoltage protection basic circuit 3 includes the thyristor SCR. 1 and the constant voltage diode TVS. 1, resistor R1.1, resistor R2.1, capacitor C2.1, and diode D2.1, the thyristor SCR. 1 is connected to the load ground terminal, its cathode is connected to the AC input terminal, and the constant voltage diode TVS. 1 cathode and thyristor SCR. 1 is connected to the gate electrode of the constant voltage diode TVS. 1 is connected to the resistors R1.1 and R2.1, which are parallel to each other, the resistor R1.1 is directly connected to the load ground terminal, and the resistor R2.1 is installed in the opposite direction to the constant voltage diode. Is connected to the load ground end, and the capacitor C2.1 is connected to the thyristor SCR. 1 cathode and constant voltage diode TVS. 1 is connected to the cathode of one, and a diode D3.1 is installed in the overvoltage protection circuit 1, the anode of the diode D3.1 is connected to the common earth terminal, the cathode is connected to the load earth terminal, A diode D3 is installed, the diode D3 is connected to the connection line between the common ground end and the load ground end, the anode of the diode D3 is connected to the cathode of the capacitor C1, and the cathode of the diode D3 is connected to the overvoltage protection circuit 1. It is connected to the anode of our diode D3.1 and energized. Compared with the single-phase full-wave overvoltage protection basic circuit of the third embodiment, the circuit utilizes the symmetry of the positive and negative half cycles of the AC input power supply, and thus the resistor R3, the resistor R3.1, the diode D1, the diode D1. Parts such as No. 1 are no longer needed, the functions of the single-phase full-wave overvoltage protection basic circuit are achieved in the same way, the circuit is simplified, and the cost is increased.

  In the specific embodiments described herein, the gist of the present invention has been described by way of example. The person skilled in the art can replace the above-mentioned embodiments with various modifications, supplements, or similar methods, but deviates from the gist of the present invention or exceeds the scope defined by the appended claims. Can not.

  In this text, even if many technical terms such as thyristor SCR, constant voltage diode TVS, resistor R1, capacitor C1, and diode D1 are used, the possibility of using other technical terms is not excluded. The use of such terminology is merely for the purpose of description and interpretation of the invention, and interpreting them as any solidarity limitation violates the spirit of the invention.

Claims (3)

In the overvoltage protection circuit for each switch power supply cycle, one overvoltage protection circuit 1 is connected between the AC input and the load. The overvoltage protection circuit 1 includes a thyristor, a constant voltage diode, a first resistor, and a second resistor. And a second diode and a second capacitor, the anode of the thyristor is connected to the AC input terminal, the cathode is connected to the load terminal, the cathode of the constant voltage diode and the gate electrode of the thyristor, The anode of the constant voltage diode is connected to a first resistor and a second resistor that are parallel to each other, the first resistor is directly connected to the AC input terminal, and the second resistor is installed in the opposite direction to the constant voltage diode. It is connected to the AC input end by being connected to the second diode, the second capacitor is connected between the cathode of the cathode and the constant voltage diode thyristor, the load end Is first condenser connected between the load ground end, further, between the cathode and the load end of the thyristor, the first diode is installed to be connected to a thyristor in the same direction, and the anode of the first diode and the common ground terminal during, Ru third resistor is connected, the overvoltage protection circuit of each switch power cycle, characterized in that. A third diode, the cathode of the third diode being connected in series with the third resistor;
Its anode is connected to the common ground terminal, the overvoltage protection circuit of each switch power cycle according to claim 1, wherein a. In the overvoltage protection circuit for each switch power cycle, one overvoltage protection circuit 1 is connected between the AC input and the load. The overvoltage protection circuit 1 includes a first thyristor, a first constant voltage diode, a first resistor, , A second resistor, a first diode, a first capacitor and a second capacitor, the anode of the first thyristor is connected to the AC input terminal, the cathode is connected to the load terminal, and the first constant voltage The cathode of the diode and the gate electrode of the first thyristor are connected, the anode of the first constant voltage diode is connected to the first resistor and the second resistor, respectively, and the first resistor is directly connected to the AC input terminal. The second resistor is connected to the AC input terminal by being connected to the first diode installed in the opposite direction to the first constant voltage diode, and the second capacitor is connected to the first thyristor. And a cathode of the first constant voltage diode, a first capacitor is connected between the load end and the load ground end, and the overvoltage protection circuit 1 further includes a second diode and a third diode. The anode of the second diode is connected to the common ground end, the cathode is connected to the load end, the third diode is connected to the connection line between the common ground end and the load ground end, and the anode of the third diode is the first is connected to the cathode of the capacitor, the cathode of the third diode is connected to the anode of the second diode, between the AC input and the load ground, the overvoltage protection circuit 2 is connected, the overvoltage protection circuit 2, a second and thyristor, a second constant-voltage diode, and a third resistor, a fourth resistor, a third capacitor, a fourth diode, an anode of the second thyristor is connected to the load ground end, Cathode is connected to the AC input ends, the cathode of the second zener diode is connected to the gate electrode of the second thyristor, a third resistor and a fourth resistor anode of the second zener diode are parallel to each other Connected, the third resistor is directly connected to the load ground terminal, the fourth resistor is connected to the fourth diode connected in the opposite direction to the second constant voltage diode, and is connected to the load ground terminal, and the third capacitor is An overvoltage protection circuit for each switch power cycle, wherein the overvoltage protection circuit is connected between a cathode of a second thyristor and a cathode of a second constant voltage diode .

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