WO2010124413A1

WO2010124413A1 - Cycle-by-cycle over voltage protection circuit for switching power supply

Info

Publication number: WO2010124413A1
Application number: PCT/CN2009/000456
Authority: WO
Inventors: 卢东方; 符平凡
Original assignee: Lu Dongfang
Priority date: 2009-04-28
Filing date: 2009-04-28
Publication date: 2010-11-04
Also published as: JP5330548B2; KR101171739B1; JP2012519462A; KR20100128353A

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

Switching power supply cycle-by-cycle overvoltage protection circuit

The present invention relates to an overvoltage protection technique, and more particularly to a switching power supply input overvoltage protection circuit. Background technique

In some cases where the power supply environment is more complicated and harsh, such as when the grid voltage is unstable, 220VAC and 380VAC are difficult to distinguish, the power input terminal inputs excessive voltage, because the internal components in the switching power supply part of the electrical equipment include the storage. Capacitors and the like are often damaged by excessive voltage, which affects the normal operation of the entire electrical appliance. In order to protect electrical equipment in this case, a common method is to add an overvoltage protection circuit at the input of the power supply. There are usually the following protection methods. Method 1: The positive temperature coefficient fuse PTCC and the metal oxide varistor M0V are jointly protected. As shown in Fig. 1, when the input of the AC input terminal is higher than a certain value, the resistance value of the varistor decreases sharply, forming In the high current loop, the PPTC is converted into a high-impedance state due to rapid heating by a large current, and the current through the line is very limited to achieve the purpose of protecting the power supply circuit; but the disadvantage is that the varistor has a short service life. The response time is slow, and once the protection is started, the power must be turned off. After the PPTC is cooled back to the low resistance state, it can continue to work. Method 2: Method 2 is a modified version of Method 1. The Zener is used instead of the varistor. As shown in Figure 2, the Zener overcomes the shortcomings of the varistor, has a very fast response time, and has a long service life. The consistency of the bit voltage is high. When the input voltage of the AC input terminal is higher than the clamp voltage of the Zener diode, the Zener diode is broken down, the impedance of the Zener diode is immediately reduced, and the voltage is clamped in the Zener diode. On the clamp voltage, a large current loop is formed, and the PPTC is converted into a high-resistance state due to rapid heat generation by passing a large current. Description

The current limit is very small, which achieves the purpose of protecting the power supply circuit. However, the shortcoming is that once the protection is started, the power must be cut off, and the PPTC should be cooled and returned to the low resistance state before it can continue to work normally. Method 3: Using thyristor overvoltage protection method, as shown in Figure 3, when the AC input voltage rises to the set voltage of the protection circuit (change the Rl, R2 resistance value can change the set voltage), the trigger diode DS is turned on, The thyristor is turned on, the current passes through the PPTC, the thyristor current limiting resistor R3, and the thyristor form a large current loop. The PPTC is converted into a high-resistance state due to rapid heating by a large current, and the current through the line is very limited, and the protection power source is reached. The purpose of the post-stage circuit. However, the disadvantage is that once the protection of the PPTC is started, the power must be cut off, and the PPTC can be cooled after returning to the low-resistance state. Method 4: Using the thyristor voltage limiting protection method, as shown in Figure 4, the principle is: The control circuit controls the conduction time of the thyristor by comparing and calculating the circuit according to the magnitude of the AC input voltage, and outputting an appropriate delay trigger pulse. The voltage of the circuit of the switching power supply does not exceed the maximum operating voltage. Although this protection method is good, the control circuit is very complicated, and the implementation cost is high, and it is not easy to use in a small power switching power supply. Method 5: Using relay overvoltage protection method, when the AC input voltage rises, the rectified DC voltage also rises. When the DC voltage is higher than the clamp voltage of the Zener diode, the Zener diode breaks down, and the transistor Q1 Conduction, relay action, normally closed electric shock, cut off the power line of the rear stage, and achieve the purpose of input overvoltage protection. Although this method is simple and reliable, its disadvantage is that in the case of large voltage fluctuations, the relay frequently operates, which has an impact on the continuous and stable power supply of the power supply. Since the protection circuit is added with a relay, it is necessary to provide a power supply for the relay to work, which is troublesome. It is bulky and difficult to use in low-power switching power supplies. Summary of the invention

The invention mainly solves the problems existing in the prior art mentioned above, and provides a principle of using a thyristor AC chopping circuit to directly sample a grid voltage and automatically change the thyristor according to the magnitude of the AC input voltage. The on-time power switch overvoltage protection circuit. The above technical problem of the present invention is mainly solved by the following technical solutions: A switching power supply per-cycle overvoltage protection circuit, characterized in that: an overvoltage protection circuit 1 is connected between the AC input and the load, the overvoltage The protection circuit includes a thyristor, a Zener diode, a first resistor, a second resistor, a second diode and a second capacitor. The anode of the thyristor is connected to the AC input terminal, and the cathode is connected to the load terminal. The cathode is connected to the gate of the thyristor, and the anode of the Zener diode is respectively connected to the first resistor and the second resistor which are connected in parallel with each other, the first resistor is directly connected to the AC input terminal, and the second resistor is connected to the Zener diode through the connection Set of second diode books

After being connected to the AC input terminal, the second capacitor is connected between the thyristor cathode and the Zener diode; a first capacitor is connected between the load input terminal and the load ground terminal. As a preferred solution of the above solution, a first diode connected in the same direction as the thyristor is disposed between the thyristor cathode and the load terminal. As a preferred solution of the above solution, a third resistor is connected between the first diode anode and the common ground terminal. As a preferred solution of the above solution, the third diode further includes a cathode of the third diode connected in series with the third resistor, a cathode connected to the third resistor, and an anode connected to the common ground. As a preferred solution of the foregoing solution, an overvoltage protection circuit 2 is connected between the AC input and the load, and the single-phase overvoltage protection circuit 2 includes a thyristor, a Zener diode, a first resistor, a second resistor, and a second resistor. a three-resistor, a first diode, a second diode, a third diode, and a second capacitor, wherein the anode of the thyristor is connected to the common ground end, and the cathode thereof is connected to the first two poles connected in series with the thyristor The tube is connected to the load end, the anode of the Zener tube is connected to the gate of the thyristor, and the cathode of the Zener tube is respectively connected to the first resistor and the second resistor connected in parallel with each other, and the first resistor is directly connected to the common ground end, Two resistors pass Description

Connecting a second diode disposed in the same direction as the Zener diode and connecting to the common ground terminal, the second capacitor is connected between the cathode of the thyristor and the anode of the Zener diode, and the third resistor is arranged in series with the third diode in the first Between the anode of the diode and the input of the alternating current, the cathode of the third diode is connected to the third diode, and the anode thereof is connected to the alternating current input.

As a preferred solution of the foregoing solution, an overvoltage protection circuit 3 is connected between the AC input terminal and the load ground terminal, and the overvoltage protection circuit 3 includes a thyristor, a Zener diode, a first resistor, a second resistor, and a second a capacitor and a second diode, the anode of the thyristor is connected to the ground end of the load, the cathode is connected to the AC input end, the cathode of the Zener tube is connected to the gate of the thyristor, and the anode of the Zener tube is respectively connected to the parallel connection On a resistor and a second resistor, the first resistor is directly connected to the load ground, the second resistor is connected to the load ground by connecting a second diode opposite to the Zener diode, and the second capacitor is connected to the cathode of the thyristor Between the Zener and the Zener.

As a preferred solution of the above solution, a third diode is disposed in the overvoltage protection circuit, the diode anode is connected to the common ground end, and the cathode is connected to the load end.

As a preferred solution of the foregoing solution, a third diode is further disposed, the third diode is connected to the common ground end and the load ground end, and the anode of the third diode is connected to the first capacitor cathode. The cathode of the third diode is in communication with the third diode anode of the overvoltage protection circuit.

Therefore, the invention utilizes the principle of thyristor AC chopping, directly samples the grid voltage, automatically changes the conduction time of the thyristor according to the magnitude of the AC input voltage, and achieves the cycle-by-cycle control of the AC input power source, thereby avoiding the disadvantage of slow response time. It can automatically and instantly correct the fluctuation of the grid voltage, thus achieving over-voltage protection for the power line of the latter stage. DRAWINGS Description

Figure 1 is a first circuit diagram of the prior art;

Figure 2 is a second circuit diagram of the prior art;

Figure 3 is a third circuit diagram of the prior art;

Figure 4 is a fourth circuit diagram of the prior art;

Figure 5 is a fifth circuit diagram of the prior art;

Figure 6 is a basic circuit diagram of single-phase half-wave overvoltage protection according to the present invention;

Figure 7 is a schematic diagram of a single-phase half-wave overvoltage protection extended circuit of the present invention;

Figure 8 is a basic circuit diagram of single-phase full-wave overvoltage protection according to the present invention;

Figure 9 is a schematic diagram of a single-phase full-wave overvoltage protection extended circuit of the present invention;

Figure 10 is a schematic diagram of a waveform of a single-phase half-wave overvoltage protection basic circuit;

Figure 11 is a schematic diagram showing the voltage waveform of the point A of the single-phase half-wave overvoltage protection basic line. detailed description

The technical solution of the present invention will be further described in detail below by way of embodiments and with reference to the accompanying drawings. Example 1:

According to the single-phase half-wave overvoltage protection basic circuit shown in FIG. 6, it is disposed between the AC input and the load, and is composed of an overvoltage protection circuit-1 and a diode D1, a resistor R3, and a capacitor C1; the single-phase half-wave pass The structure of the voltage protection basic circuit is: comprising a crystal SCR, the anode of the thyristor SCR is connected to the AC input end, and the cathode is connected to the load end by connecting the diode D1 disposed in the same direction as the thyristor SCR, and further comprises a voltage regulator. The TVS is connected to the gate of the thyristor SCR, and the anode of the Zener diode TVS is respectively connected to the resistor R1 and the resistor R2 which are connected in parallel with each other. The resistor R1 is directly connected to the AC input terminal, and the resistor R2 is connected through The Zener diode TVS is reversely set with the diode D2 and the AC input Connected to the input terminal, a capacitor C2 is connected between the thyristor SCR cathode and the Zener diode TVS cathode, and a resistor R3 is also provided. The resistor R3 is disposed between the anode of the diode D1 and the AC input terminal, between the load input end and the load ground end. A capacitor Cl is connected. The thyristor SCR, the diode D1, and the capacitor C1 constitute a current output main circuit; the resistor R1, the TVS voltage regulator, the capacitor C2, and the resistor R3 constitute a control loop 1 for generating a thyristor trigger pulse; the diode D2, the resistor R2, the TVS The Zener diode, the capacitor C2, and the resistor R3 constitute a control loop 2 for generating a thyristor trigger pulse. The working principle of this circuit is as follows: When the AC input is in the initial stage of the positive half cycle, the pulse-trigger end A of the thyristor SCR is low-voltage book.

In the flat state, the voltage at point A is as shown in Fig. 11, the thyristor SCR is turned off, at which time the C voltage is higher than point B, the diode D1 is in the reverse-off state, and the storage capacitor C1 is not discharged in the opposite direction to the input circuit; The voltage gradually rises, and the current is positively charged to the capacitor C2 through the control loop one, that is, the resistor R1, the TVS voltage regulator, and the resistor R3. At this time, the voltage regulator TVS is in the forward conduction state, and the voltage gradually increases with the positive half cycle of the AC input. Ascending, the voltage at point A also gradually rises. When the voltage at point A exceeds the gate trigger voltage V _SCR of the thyristor, the thyristor SCR is turned on, the capacitor C2 is charged, and the forward charging time for the capacitor C2 is called T _C2+ (eg Figure 10); After the thyristor SCR is turned on, the voltage at point B gradually rises. When the voltage at point B exceeds the voltage at point C V _C1 (voltage at voltage C1) +0. 7V (forward voltage drop of diode D1), D1 On, the current is charged to the capacitor C1 through the main circuit, and the voltage at point C is gradually increased. As the voltage in the positive half cycle gradually decreases, the voltage at point B also gradually decreases. When the voltage at point B is lower than the voltage at point C, D1 is turned off, and the capacitor is turned off. C1 charging junction , The charging time of the capacitor C1 is referred to as T _C1 (FIG. 10); due to the large resistance of resistor R3, the current flowing through the thyristor SCR is less than the holding current of the thyristor, the thyristor SCR is turned off, the output of the main circuit current is cut off, the thyristor The on-time of the SCR is called! ^ (as shown in Figure 10). At this time, the current flowing through the thyristor SCR is greater than its holding current, and the SCR is turned on, but with the loss Description

When the input voltage is reduced to zero, the thyristor SCR will also turn off by itself, cutting off the current output main circuit.

Since the charging time T _{C1 of the} capacitor C1 is proportional to the on-time of the thyristor SCR, the longer the on-time T _{SCR of} the thyristor SCR is, the higher the voltage V _C1 on the capacitor C1 is; the conduction of the thyristor SCR is controlled by the gate. When the gate reaches the trigger voltage V _OT , the thyristor SCR is turned on. The longer the time T _{C2+ of} the voltage at point A reaches V _sca , the smaller the on-time T _{sai of the} thyristor SCR is, and the lower the voltage on the storage capacitor C1 is. Therefore, as long as the positive charging time T _C2+ of C2 is controlled, the voltage on the capacitor C1 can be within the safe use range, thereby achieving the purpose of protecting the load circuit. However, this must be based on the assumption that the AC input voltage is stable. If the AC input voltage suddenly rises, the charging current in the control loop 1 increases accordingly. The time T _C2+ reaches the gate trigger voltage V _SCR is shortened, and the thyristor SCR conduction time is extended. , the charging time T _C1 on the capacitor C1 is prolonged, and the voltage on the capacitor C1 is also increased accordingly, so it is also necessary to cooperate with the control loop 2 to solve the charging time on the pair of capacitors C1 of the control loop! ^ Control.

During the positive half cycle of the AC input, the diode D2 in the control circuit 2 is reversely turned off, and the control circuit 2 does not function. When the negative half cycle period is entered, the Zener diode TVS is not conducting and is high due to the small negative voltage. In the impedance state, there is only a small leakage current in the control loop, which has little effect on the voltage at point A, and the voltage at point A is basically unchanged. As the negative voltage increases, when the negative voltage exceeds the clamp voltage V _TVS of the Zener diode TVS, the impedance of the Zener diode TVS decreases immediately, and the voltage is clamped to the clamp voltage of the Zener diode TVS. In the control circuit 2, a reverse charging circuit is formed for the capacitor C2, so that the voltage at the point A has a positive pressure and the negative voltage at the point A is called V _C2 ―, and the charging time for the C2 is called T (as shown in the figure). 10)). If the AC input voltage increases (AC input negative pressure increases), the reverse charging current increases and the reverse charging time T _C2 of the capacitor C2 increases due to the breakdown time of the TVS tube of the Zener tube; C2 is charged The increase in time and the increase in charging current cause A to form a higher negative pressure V _e2 -. The magnitude of the negative voltage V _C2 - formed at point A affects the positive charging time of capacitor C2 in the positive half cycle of the AC input. The higher the negative voltage V _ra - of point A, Instruction manual

When C2 reaches the thyristor SCR at the forward charging time, the _longer the time Tc2 _{+ of} the thyristor voltage V _seR is triggered, the shorter the on-time T _{OT of the} thyristor SCR is shortened, thereby reducing the charging time T _C1 of the capacitor C1 , the capacitance C1 The voltage V _{ei is} also reduced, achieving the purpose of protecting the load.

Conversely, the AC input negative voltage is reduced, the reverse charging current is decreased, and the reverse charging time I of the capacitor C2 is shortened due to the delay of the breakdown time of the Zener diode TVS, and the capacitor C2 is shortened due to the charging time and the charging current is reduced. As the point A forms a lower negative voltage V _ra —, the time for the capacitor C2 to reach the thyristor SCR triggering the turn-on threshold voltage ¥ _在 at the forward charging time is shortened, thereby increasing the charging time 电容 of the capacitor C1 , the capacitor C1 The voltage T _ei also rises, thereby ensuring that the voltage across the capacitor C1 is stable.

Generally, the voltage values of the positive and negative half cycles of the AC input voltage are equal. Since the resistor R1 in the control loop 1 still functions during the negative half cycle of the AC input, the reverse charging current to the capacitor C2 is greater than that in the AC. Input the positive charging current of capacitor C2 in the positive half cycle, and select the component parameters in circuit one and circuit two properly. When the AC input voltage exceeds the specified safety voltage (such as greater than 320AC), the voltage at point A is at the AC input. During the positive half cycle, the thyristor threshold voltage can be reached, the thyristor cannot be turned on, and the power input loop is cut off, thereby protecting the safety of the load.

Control loop one, loop two pairs of AC input power supply to achieve each wave of control, automatic chopping voltage limit, for sudden boost, up to a positive half cycle, and only one positive half cycle voltage, capacitor C1 and load often It is completely capable of being digested without damaging the circuit components, thus completely ensuring the safety of the load.

Example 2:

As shown in FIG. 7, a single-phase half-wave overvoltage protection extension line is provided, which is basically the same as the single-phase half-wave overvoltage protection basic circuit structure in Embodiment 1, but further includes a diode D3. The cathode of the diode D3 is connected in series with the resistor R3, and the cathode thereof is connected to the resistor R3, and the anode and the common ground end Description

Connected. Compared with the first embodiment, when the AC input positive half cycle is in the initial stage, the circuit only starts to charge the capacitor C2 positively when the input positive half cycle voltage is greater than the voltage on the capacitor C1, delaying the capacitance. C2 forward charging time, that is, shortening the conduction time of the thyristor SCR, reducing the charging time of the capacitor C1, the voltage of the capacitor C1 is reduced, thereby protecting the load; the resistor R3 is blocked by the reverse of the diode D3 It does not work; in the negative half cycle of the AC input, the diode D3 is in the forward state, and the reverse charging of the capacitor C2 in the loop 2 is the same as in the first embodiment.

Example 3:

According to Fig. 8, the present invention also provides a single-phase full-wave overvoltage protection basic circuit. The circuit structure is connected with an overvoltage protection circuit 2 between the AC input and the load on the line of the embodiment 2. The single-phase overvoltage protection circuit 2 includes a thyristor SCR.1 and a Zener diode TVS.1. , the resistor Rl.l, the resistor R2.1, the resistor R3.1, the diode Dl.l, the diode D2.1, the diode D3.1 and the capacitor C2.1, the anode of the thyristor SCR.1 is connected to the common ground end, The cathode is connected to the load terminal through a diode D1.1 connected in series with the thyristor SCR.1, and the anode of the Zener diode TVS.1 is connected to the gate of the thyristor SCR.1, and the cathode of the Zener diode TVS.1 is respectively Connected to the resistor R1.1 and the resistor R2.1 connected in parallel with each other, the resistor R1.1 is directly connected to the common ground terminal, and the resistor R2.1 is connected to the diode D2.1 disposed in the same direction as the Zener diode TVS.1. The common ground is connected, the capacitor C2.1 is connected between the thyristor SCR.1 cathode and the Zener diode TVS.1 anode, and the resistor R3.1 is connected in series with the diode D3.1 between the anode of the diode D1.1 and the AC input terminal. The cathode of the diode D3.1 is connected to the diode D3.1, and the anode thereof is connected to the alternating current input terminal. The working principle is the same as that of Embodiment 1. In Embodiments 1 and 2, the capacitor C1 is charged only during the positive half cycle of the AC input, and the capacitor C1 cannot be charged during the negative half cycle of the AC input. In this embodiment, the capacitor C1 can be charged in the positive and negative half cycles of the AC input, and the voltage on the capacitor C1 is stabilized. Embodiment 4: According to Fig. 9, the present invention also provides a single-phase full-wave overvoltage protection extension circuit. The circuit includes an overvoltage protection circuit-1, and an overvoltage protection circuit 3 is connected between the AC input terminal and the load ground terminal. The overvoltage protection circuit 3 includes a thyristor SCR.1, a Zener diode TVS.1, and a resistor. Rl.l, resistor R2.1, capacitor C2.1 and diode D2.1, the anode of the thyristor SCR.1 is connected to the load ground, and the cathode is connected to the AC input terminal. The Zener and the thyristor of the Zener diode TVS.1 The gates of SCR.1 are connected, and the anodes of the Zener diodes TVS.1 are respectively connected to the resistors R1.1 and R2.1 which are connected in parallel with each other. The resistor R1.1 is directly connected to the ground of the load, and the resistor R2.1 passes. Connect the diode D2.1 opposite to the Zener diode and the load ground

Connected, capacitor C2.1 is connected between the thyristor SCR.1 cathode and the Zener diode TVS.1 cathode. In the overvoltage protection circuit-1, a diode D3.1 is further disposed, the anode of the diode D3.1 is connected to the common ground end, the cathode is connected to the load end, and a diode D3 is further disposed, and the diode D3 is connected at a common ground end. Connected to the ground of the load, the anode of the diode D3 is in communication with the cathode of the capacitor C1, and the cathode of the diode D3 is connected to the anode of the diode D3.1 in the overvoltage protection circuit 1. Compared with the single-phase full-wave overvoltage protection basic circuit in the third embodiment, the circuit utilizes the symmetry of the positive and negative half cycles of the AC input power source, and reduces the resistance R3, the resistance R3.1, the diode D1, and the diode D1.1. The component also achieves the function of the single-phase full-wave overvoltage protection basic circuit, which simplifies the circuit and reduces the cost. The specific embodiments described herein are merely illustrative of the spirit of the invention. A person skilled in the art can make various modifications or additions to the specific embodiments described, or in a similar manner, without departing from the spirit of the invention or as defined by the appended claims. The scope. Although the terms of the thyristor SCR, the voltage regulator TVS, the resistor R1, the capacitor Cl, the diode D1, etc. are used in this article, the possibility of using other terms is not excluded. Use these terms just to be more square Description

The nature of the invention is described and explained in detail; the interpretation of any of the additional limitations is inconsistent with the spirit of the invention.

Claims

Claim

A switching power supply per-cycle overvoltage protection circuit, characterized in that:

An overvoltage protection circuit 1 is connected between the AC input and the load, and the overvoltage protection circuit includes a thyristor, a Zener diode, a first resistor, a second resistor, a second diode, and a second capacitor, and the thyristor The anode is connected to the AC input end, the cathode is connected to the load end, the cathode of the Zener tube is connected to the gate of the thyristor, and the anode of the Zener tube is respectively connected to the first resistor and the second resistor connected in parallel with each other, the first resistor is directly Connected to the AC input terminal, the second resistor is connected to the AC input terminal by connecting a second diode opposite to the Zener diode, and the second capacitor is connected between the cathode of the thyristor and the cathode of the Zener tube;

A first capacitor is connected between the load input terminal and the load ground terminal.

2. The switching power supply cycle-by-cycle overvoltage protection circuit according to claim 1, wherein a first diode connected in the same direction as the thyristor is disposed between the thyristor cathode and the load terminal.

3. The switching power supply cycle-by-cycle overvoltage protection circuit according to claim 2, wherein a third resistor is connected between the anode of the first diode and the common ground.

4. The switching power supply cycle-by-cycle overvoltage protection circuit according to claim 3, further comprising a third diode, the cathode of the third diode being connected in series with the third resistor, the cathode and the third resistor Connected, the anode is connected to the common ground.

The cycle-by-cycle overvoltage protection circuit for a switching power supply according to claim 4, wherein an overvoltage protection circuit 2 is connected between the AC input and the load, and the single phase overvoltage protection circuit 2 includes a thyristor and is stable. a pressure tube, a first resistor, a second resistor, a third resistor, a first diode, a second diode, a third diode, and a second capacitor, wherein an anode of the thyristor is connected to a common ground end, and a cathode thereof passes through The first diode connected in series with the thyristor is connected to the load end, and the anode of the Zener tube is connected to the gate of the thyristor, and the cathodes of the Zener tube are respectively connected to the first resistor and the second resistor connected in parallel with each other. The first resistor is directly connected to the common ground, and the second resistor is connected to the common ground by connecting the second diode in the same direction as the Zener diode

Claims

The second capacitor is connected between the thyristor cathode and the anode of the Zener tube, and the third resistor is disposed in series with the third diode between the first diode anode and the AC input terminal, the third diode The cathode is connected to the third diode, and the anode is connected to the alternating current input.

6. The switching power supply per-cycle overvoltage protection circuit according to claim 1, wherein an overvoltage protection circuit 3 is connected between the AC input terminal and the load ground terminal, and the overvoltage protection circuit 3 includes a thyristor and a voltage regulator. a tube, a first resistor, a second resistor, a second capacitor and a second diode, wherein the anode of the thyristor is connected to the ground end of the load, and the cathode is connected to the AC input end, and the cathode of the Zener tube is connected to the gate of the thyristor The anodes of the Zener diodes are respectively connected to the first resistor and the second resistor connected in parallel with each other, the first resistor is directly connected to the ground end of the load, and the second resistor is connected to the second diode disposed opposite to the Zener diode The load ground is connected, and the second capacitor is connected between the thyristor cathode and the Zener cathode.

The cycle-by-cycle overvoltage protection circuit for a switching power supply according to claim 6, wherein a third diode is disposed in the overvoltage protection circuit, the anode of the diode is connected to the common ground, and the cathode and the load end thereof are provided. Connected.

The switching power supply per-cycle overvoltage protection circuit according to claim 7, wherein a third diode is further disposed, and the third diode is connected to the common ground end and the load ground end, The anode of the three diode is in communication with the first capacitor cathode, and the cathode of the third diode is in communication with the third diode anode of the overvoltage protection circuit.