Input overvoltage protection circuit of switching power supply

Abstract

The utility model relates to an input overvoltage protection circuit of a switching power supply, which comprises a switching circuit, a control circuit and a voltage sampling circuit, and the input overvoltage protection circuit of the switching power supply has the effects of fewer external circuit devices, high accuracy, low cost and higher universality by using a controllable precision voltage stabilization source.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to an input overvoltage protection circuit of a switching power supply. Background Art

[0002] As a power supply device for electronic products, the switching power supply must not only meet the requirements of power supply products in terms of basic performance, but also have its own protection measures, such as overvoltage, overcurrent and overheating protection. When the switching power supply is accidentally connected to high voltage, if there is no input overvoltage protection function, the power supply cannot turn off the output voltage, and the high voltage will burn the IC chip, power MOSFET and output side equipment, and even cause electric shock and fire to the operator. Although in the prior art, some main control chips have input overvoltage protection function, the price of such main control chips is relatively high. Utility Model Content

[0003] In view of this, it is necessary to provide an input overvoltage protection circuit which has a simple circuit and can perform overvoltage protection on the input voltage of a switching power supply when the main control chip does not have an overvoltage protection function.

[0004] Typically, a switching power supply includes a main control chip and a rectifier circuit. The rectifier circuit connects the DC voltage after the AC voltage is rectified to the main control chip through a DC bus. The main control chip converts the DC voltage of the rectifier circuit into a power supply under the control of a switching signal. An input overvoltage protection circuit of a switching power supply includes a switching circuit, a control circuit and a voltage sampling circuit. The input end of the voltage sampling circuit is connected to the DC bus to sample the DC voltage. The output end of the voltage sampling circuit is connected to the control input end of the control circuit. The output end of the switching circuit is connected to the voltage sampling pin of the main control chip. The control input end of the switching circuit is connected to the control signal output end of the control circuit.

[0005] Furthermore, the switching circuit includes a phototransistor OT1-A of an optical coupler OT1, the collector of the phototransistor OT1-A is connected to the voltage sampling pin of the main control chip U1 as the output end of the switching circuit, the emitter of the phototransistor OT1-A is grounded, and the switching circuit outputs a switching signal to control the main control chip U1 to perform power conversion.

[0006] Furthermore, the voltage sampling circuit includes a voltage divider circuit, which includes a resistor R13, a resistor R14, and a resistor R15. One end of the resistor R13 is connected to one end of the resistor R14 and one end of the resistor R15, and the other end of the resistor R14 and the other end of the resistor R15 are grounded to form a voltage divider circuit. The other end of the resistor R13 is the input end of the voltage divider circuit and is connected to the DC bus. The connection point between one end of the resistor R13, one end of the resistor R14, and one end of the resistor R15 is the output end of the voltage divider circuit. The output end of the voltage divider circuit is connected to the reference end of the controllable precision voltage stabilizing source U3.

[0007] Furthermore, the voltage divider circuit also includes a bidirectional diode D16 and a capacitor C40, wherein the first end of the bidirectional diode D16 is connected to the first end of the capacitor C40, the second end of the bidirectional diode D16 is connected to the first end of the resistor R13, and the second end of the capacitor C40 is connected to the second end of the resistor R13.

[0008] Furthermore, the control circuit includes a controllable precision voltage-stabilizing source U3, a voltage-stabilizing tube Z2, a resistor R2, a resistor R3, a resistor R10, a resistor R11, and a transistor Q1. One end of the resistor R11 is connected to the DC bus, and the other end of the resistor R11 is connected to the negative electrode of the controllable precision voltage-stabilizing source U3. The resistor R11 is a bias resistor to supply power to the controllable precision voltage-stabilizing source U3, provide a stable working current, and ensure that the controllable precision voltage-stabilizing source U3 works stably. One end of the resistor R10 is connected to the DC bus, and the resistor The other end of R10 is connected to the positive electrode of the light emitting diode OT1-B of the optocoupler OT2 to power the light emitting diode OT1-B of the optocoupler OT2, one end of the capacitor C44 is connected to the reference electrode of the controllable precision voltage stabilizing source U3, the other end of the capacitor C44 is connected to the negative electrode of the controllable precision voltage stabilizing source U3 as a filter capacitor of the controllable precision voltage stabilizing source U3, the negative electrode of the voltage stabilizing tube Z2 is connected to the DC bus, the negative electrode of the voltage stabilizing tube Z2 is connected to the resistor R2 and one end of the resistor R3, and the other end of the resistor R3 is the base of the transistor Q1;

[0009] Furthermore, the control circuit further includes a first capacitor C7, which is a filter capacitor of the base of the transistor Q1, a first end of the first capacitor C7 is connected to the transistor Q1, and a second end of the first capacitor C7 is grounded. One end of the capacitor C7, the other end of the resistor R2 and the other end of the capacitor C7 are grounded, and the capacitor C7 serves as a filter capacitor of the transistor Q1.

[0010] Furthermore, the control circuit also includes a second capacitor C10, a third capacitor C44, and a resistor R12. The first end of the third capacitor C44 is connected to the reference electrode of the controllable precision voltage-stabilizing source U3 and the first end of the second capacitor C10, and the second end of the third capacitor C44 is connected to the negative electrode of the controllable precision voltage-stabilizing source U3. The capacitor C44 serves as a filter capacitor of the controllable precision voltage-stabilizing source U3. The second end of the second capacitor C10 is connected to the first end of the resistor R12, and the second end of the resistor R12 is connected to the output end of the voltage divider circuit. The second capacitor C10 and the resistor R12 are connected in series to form a loop to absorb low-frequency interference at the output end of the voltage divider circuit.

[0011] Furthermore, when the voltage across the voltage regulator Z2 exceeds the voltage regulation value, current flows through the base of the transistor Q1, which is in the amplification region. The collector and emitter of the transistor Q1 are in a low-resistance state, and the current flowing through the optocoupler diode OT1-B passes through the emitter of the transistor Q1 and the collector of the transistor Q1 directly to the ground, so that the output of the switching power supply is 0, thereby achieving overvoltage protection; the negative electrode of the controllable precision voltage regulator U3 is connected to the negative electrode of the light-emitting diode OT1-B of the optocoupler OT1, the positive electrode of the controllable precision voltage regulator U3 is grounded, the reference electrode of the controllable precision voltage regulator U3 is the input end of the control circuit, and a reference voltage is provided inside the controllable precision voltage regulator U3. The output voltage of the voltage divider circuit is connected to the reference electrode of the controllable precision voltage regulator U3 and is compared with the reference voltage inside the controllable precision voltage regulator U3. The control circuit outputs a signal to the input end of the switching circuit, and the optocoupler OT1 of the control switching circuit outputs a control signal.

[0012] When the input voltage of the switching power supply increases, the output voltage of the voltage divider circuit of the voltage sampling circuit also increases. When the output voltage of the voltage divider circuit is higher than the reference voltage, the negative electrode and the positive electrode of the controllable precision voltage regulator U3 are connected, the light-emitting diode OT1-B is turned on, and the light-controlled signal is output to the base of the phototransistor OT1-A. The phototransistor OT1-A is turned on, and the collector of the phototransistor OT1-A outputs a low-voltage shutdown signal, causing the voltage of the voltage sampling pin of the main control chip to become low, so that the main control chip U1 of the switching power supply enters the input over-protection state, and the optocoupler OT1 plays a role of on and off, amplifies the light-controlled signal and outputs it to the collector of the phototransistor OT1-A, and outputs a switch signal to control the switching power supply chip to enter the input over-voltage protection state.

[0013] The first end of resistor R13 is connected to the DC bus, and the second end is connected to ground through resistors R14 and R15 in sequence. The connection point between resistor R13 and resistors R14 and R15 is the output end of the voltage divider circuit, which is connected to the reference electrode of the controllable precision voltage regulator U3. The voltage is V=Vin*R14 / / R15 / (R14 / / R15+R13). The controllable precision voltage regulator U3 adopts TL431. The negative electrode of the controllable precision voltage-stabilizing source U3 is connected to the negative electrode of the light-emitting diode OT1-B of the optocoupler OT1, the positive electrode of the controllable precision voltage-stabilizing source U3 is grounded, the reference voltage of the reference electrode of the controllable precision voltage-stabilizing source U3 is 2.5V, the output voltage of the voltage-dividing circuit is compared with the reference voltage of the reference electrode of the controllable precision voltage-stabilizing source U3, when the output voltage of the voltage-dividing circuit is higher than the reference voltage, the negative electrode and the positive electrode of the controllable precision voltage-stabilizing source U3 are connected, the light-emitting diode OT1-B is turned on, and the light-controlled signal is output to the base of the phototransistor OT1-A, the phototransistor OT1-A is turned on, and the collector of the phototransistor OT1-A outputs a low-voltage shutdown signal, causing the voltage of the voltage sampling pin of the main control chip to become low, so that the main control chip U1 of the switching power supply enters the input over-protection state, and the optocoupler OT1 plays a role of on and off, amplifies the light-controlled signal and outputs it to the collector of the phototransistor OT1-A, and outputs a switch signal to control the switching power supply chip to enter the input over-voltage protection state.

[0014] The upper limit voltage of the controllable precision voltage regulator U3 of the control circuit is 36V. The second capacitor C10 is a loop capacitor, which is selected according to actual demand measurement and has a value of 0.1uF.

[0015] The collector of the optocoupler phototransistor OT1-A is connected to the voltage sampling pin of the switching power supply main control chip U1, and the emitter is connected to the ground pin of the main control chip U1. Pulling down the voltage of the voltage sampling pin can make the switching power supply main control chip U1 enter the input over-protection state, and the optocoupler plays a role of on and off.

[0016] The input overvoltage protection circuit of the above-mentioned switching power supply has a simple circuit structure, fewer external circuit components, high precision, low cost, and high versatility. It can be connected to different types of main control chips. As long as a certain pin of the main control chip is at a low level to trigger protection, this self-powered input overvoltage protection can protect electronic products and avoid the occurrence of some accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The utility model is a schematic block diagram of an input overvoltage protection circuit of a switching power supply according to an embodiment of the utility model.

[0018] Figure 2 The utility model is a circuit diagram of a switch circuit, a control circuit and a voltage sampling circuit of an input overvoltage protection circuit of a switching power supply according to an embodiment of the utility model.

[0019] Figure 3 The utility model is a circuit diagram of the input overvoltage protection circuit rectification and main control chip part of a switching power supply in an embodiment of the present utility model. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0021] Typically, a switching power supply includes a main control chip and a rectifier circuit. The rectifier circuit rectifies the AC voltage into a DC voltage that is connected to the main control chip through a DC bus. The main control chip converts the DC voltage of the rectifier circuit into a power supply under the control of a switching signal.

[0022] See also Figure 1 , Figure 2 and Figure 3 , shows an input overvoltage protection circuit of a switching power supply provided by an embodiment of the utility model, including a switching circuit, a control circuit and a voltage sampling circuit, wherein the input end of the voltage sampling circuit is connected to a DC bus to sample the DC voltage, the output end of the voltage sampling circuit is connected to the control input end of the control circuit, the output end of the switching circuit is connected to the voltage sampling pin 2 of the main control chip U1, and the control input end of the switching circuit is connected to the control signal output end of the control circuit.

[0023] Furthermore, the switching circuit includes a phototransistor OT1-A of an optical coupler OT1, the collector of the phototransistor OT1-A is connected to the voltage sampling pin 2 of the main control chip U1 of the switching power supply as the output end of the switching circuit, the emitter of the phototransistor OT1-A is grounded, and the switching circuit outputs a switching signal to control the main control chip U1 of the switching power supply to perform power conversion.

[0024] Furthermore, the voltage sampling circuit includes a voltage divider circuit, which includes a resistor R13, a resistor R14, and a resistor R15. One end of the resistor R13 is connected to one end of the resistor R14 and one end of the resistor R15 in parallel, and the other end of the resistor R14 and the other end of the resistor R15 are grounded to form a voltage divider circuit. The other end of the resistor R13 is the input end of the voltage divider circuit and is connected to the DC bus. The connection point between one end of the resistor R13 and one end of the resistor R14 and one end of the resistor R15 is the output end of the voltage divider circuit. The output end of the voltage divider circuit is connected to the reference electrode of the controllable precision voltage stabilizing source U3.

[0025] Furthermore, the voltage divider circuit also includes a bidirectional diode D16 and a capacitor C40. The first end of the bidirectional diode D16 is connected to the first end of the capacitor C40, the second end of the bidirectional diode D16 is connected to the first end of the resistor R13, and the second end of the capacitor C40 is connected to the second end of the resistor R13. The bidirectional diode D16 and the capacitor C40 are connected in series and then in parallel with the resistor R13 of the voltage divider circuit, which can prevent the startup voltage from overshooting.

[0026] Furthermore, the control circuit includes a controllable precision voltage-stabilizing source U3, a first capacitor C7, a second capacitor C10, a third capacitor C44, a voltage-stabilizing diode Z2, a resistor R2, a resistor R3, a resistor R10, a resistor R11, a resistor R12, and a transistor Q1. One end of the resistor R11 is connected to the DC bus, and the other end of the resistor R11 is connected to the negative electrode of the controllable precision voltage-stabilizing source U3. The resistor R11 is a bias resistor to power the controllable precision voltage-stabilizing source U3 and provide a stable working current to ensure that the controllable precision voltage-stabilizing source U3 works stably. One end of the resistor R10 is connected to the DC bus, and the other end of the resistor R10 is connected to the positive electrode of the light-emitting diode OT1-B in the optocoupler OT2 to power the light-emitting diode OT1-B of the optocoupler OT2. The value of the resistor R10 is 2K. One end of capacitor C44 is connected to the reference electrode of controllable precision voltage-stabilizing source U3, the other end of capacitor C44 is connected to the negative electrode of controllable precision voltage-stabilizing source U3 as a filter capacitor of controllable precision voltage-stabilizing source U3, the negative electrode of voltage-stabilizing tube Z2 is connected to the DC bus, the negative electrode of voltage-stabilizing tube Z2 is connected to resistor R2 and one end of resistor R3, the other end of resistor R3 is connected to the base of transistor Q1 and one end of capacitor C7, the other end of resistor R2 and the other end of capacitor C7 are grounded, and capacitor C7 is used as a filter capacitor of the base of transistor Q1;

[0027] The control circuit also includes a second capacitor C10, a third capacitor C44, and a resistor R12. The first end of the third capacitor C44 is connected to the reference electrode of the controllable precision voltage-stabilizing source U3 and the first end of the second capacitor C10, and the second end of the third capacitor C44 is connected to the negative electrode of the controllable precision voltage-stabilizing source U3. The capacitor C44 serves as a filter capacitor of the controllable precision voltage-stabilizing source U3. The second end of the second capacitor C10 is connected to the first end of the resistor R12, and the second end of the resistor R12 is connected to the output end of the voltage divider circuit. The second capacitor C10 and the resistor R12 are connected in series to form a loop to absorb low-frequency interference at the output end of the voltage divider circuit.

[0028] The negative pole of the controllable precision voltage-stabilizing source U3 is connected to the negative pole of the light-emitting diode OT1-B of the optocoupler OT1, the positive pole of the controllable precision voltage-stabilizing source U3 is grounded, the reference pole of the controllable precision voltage-stabilizing source U3 is the input end of the control circuit, a reference voltage is provided inside the controllable precision voltage-stabilizing source U3, the output end of the voltage-divider circuit is connected to the reference pole of the controllable precision voltage-stabilizing source U3, the output power of the voltage-divider circuit is compared with the reference voltage inside the controllable precision voltage-stabilizing source U3, the control circuit outputs a signal to the input end of the switching circuit, and the optocoupler OT1 that controls the switching circuit outputs a control signal.

[0029] When the input voltage of the switching power supply increases, the output voltage of the voltage divider circuit of the voltage sampling circuit also increases. When the output voltage of the voltage divider circuit is higher than the reference voltage of the controllable precision voltage regulator U3, the negative electrode and the positive electrode of the controllable precision voltage regulator U3 are connected, the light-emitting diode OT1-B is turned on, and the output light-control signal is emitted to the base of the phototransistor OT1-A. The phototransistor OT1-A is turned on, and the collector of the phototransistor OT1-A outputs a low-voltage shutdown signal, causing the voltage of the voltage sampling pin 2 of the main control chip U1 to become low, so that the main control chip U1 of the switching power supply enters the input over-protection state, and the optocoupler OT1 plays a role of on and off. The phototransistor OT1-A amplifies the light-control signal and outputs it to the collector of the phototransistor OT1-A, and outputs a switching signal to control the main control chip U1 of the switching power supply to enter the input over-voltage protection state.

[0030] One end of the resistor R13 of the voltage divider circuit is connected to the DC bus, and the other end is connected to the ground through the resistor R14 and the resistor R15 in sequence. The connection point of the resistor R13, the resistor R14 and the resistor R15 is the reference electrode of the controllable precision voltage stabilizing source U3 connected to the output end of the voltage divider circuit. The output voltage of the voltage divider circuit is:

[0031] V = Vin*R14 / / R15 / (R14 / / R15+R13)

[0032] In this embodiment, the model of the controllable precision voltage regulator U3 is TL431, the negative electrode of the controllable precision voltage regulator U3 is connected to the negative electrode of the light emitting diode OT1-B of the optical coupler OT1, the positive electrode of the controllable precision voltage regulator U3 is grounded, the internal reference voltage of the controllable precision voltage regulator U3 is 2.5V, the output voltage of the voltage divider circuit is compared with the internal reference voltage of the controllable precision voltage regulator U3, when the output voltage of the voltage divider circuit is higher than the reference voltage, the negative electrode and the positive electrode of the controllable precision voltage regulator U3 are connected, the light emitting diode OT1-B is turned on, the light emitting diode OT1-B emits an output light control signal to the base of the phototransistor OT1-A, the collector and emitter of the phototransistor OT1-A are turned on, the collector of the phototransistor OT1-A outputs a low voltage shutdown signal, causing the voltage sampling pin 2 of the main control chip U1 to be turned on. The voltage becomes low, causing the main control chip U1 of the switching power supply to enter the input over-protection state, and the optocoupler OT1 plays a role of on-off, amplifying the light control signal and outputting it to the collector of the phototransistor OT1-A, and outputting a switch signal to control the main control chip U1 of the switching power supply to enter the input over-voltage protection state; when the output voltage of the voltage divider circuit is lower than the reference voltage, the negative and positive electrodes of the controllable precision voltage regulator U3 are cut off, the light-emitting diode OT1-B is cut off, and the light-emitting diode OT1-B has no light control signal output to the base of the phototransistor OT1-A, the phototransistor OT1-A is cut off, and the collector of the phototransistor OT1-A outputs a high voltage signal to increase the voltage of the voltage sampling pin 2 of the main control chip U1, and exit the over-voltage protection state.

[0033] The collector of the optocoupler phototransistor OT1-A is connected to the voltage sampling pin 2 of the switching power supply main control chip U1, and the emitter is grounded together with the ground pin of the main control chip U1. The collector of the optocoupler phototransistor OT1-A outputs a low voltage to pull down the voltage of the voltage sampling pin 2 of the main control chip U1, which can make the main control chip U1 of the switching power supply enter the input over-protection state, and the optocoupler plays a role of on and off.

[0034] When the circuit is working normally, since the output voltage is 12V, the two ends of the voltage regulator Z2 have not reached the reverse breakdown value, the voltage regulator Z2 is cut off, and no current flows through the base of the transistor Q1, so the transistor Q1 is not in the working area, and the circuit operates normally through the voltage regulation loop. When the output voltage exceeds the reverse breakdown value (14.3V), the voltage regulator Z2 reversely breaks down, and the base of the transistor Q1 has current flowing through it, which is in the amplification area. The collector and emitter of the transistor Q1 are in a low-resistance state, and the current flowing through the optocoupler diode OT1-B passes through the emitter of the transistor Q1 and the collector of the transistor Q1 directly to the ground, so that the output of the switching power supply is 0, achieving overvoltage protection.

[0035] The input overvoltage protection circuit of the above-mentioned switching power supply uses a controllable precision voltage regulator, which can well realize input overvoltage protection when the main control chip does not have an overvoltage protection function. It has fewer external circuit components, high precision, low cost, and high versatility. It can be connected to main control chips of different models. As long as a pin of the main control chip can trigger protection at a low level, the input overvoltage protection circuit product of the utility model has a simple circuit structure, is easy to produce, has low cost, and is easy to promote.

[0036] It should be noted that the present invention is not limited to the above-mentioned embodiments. According to the creative spirit of the present invention, those skilled in the art may also make other changes. These changes made according to the creative spirit of the present invention should be included in the scope of protection required by the present invention.

Claims

1. An input overvoltage protection circuit for a switching power supply, characterized in that: It includes a switch circuit, a control circuit and a voltage sampling circuit. The input end of the voltage sampling circuit is connected to the DC bus to sample the DC voltage. The control circuit includes a controllable precision voltage stabilizing source U3, a voltage stabilizing tube Z2, a resistor R2, a resistor R3, a resistor R10, a resistor R11, and a transistor Q1. One end of the resistor R11 is connected to the DC bus, and the other end of the resistor R11 is connected to the negative electrode of the controllable precision voltage stabilizing source U3. One end of the resistor R10 is connected to the DC bus, and the other end of the resistor R10 is connected to the positive electrode of the optical coupler OT2. The positive electrode of the light emitting diode OT1-B is the optical coupler. The OT2 light emitting diode OT1-B is powered, the cathode of the voltage regulator tube Z2 is connected to the DC bus, the cathode of the voltage regulator tube Z2 is connected to the resistor R2 and one end of the resistor R3, the other end of the resistor R3 is the base of the transistor Q1, and the other end of the resistor R2 is grounded; the collector of the transistor Q1 is the control signal output end of the control circuit, the output end of the voltage sampling circuit is connected to the control input end of the control circuit, the output end of the switch circuit is connected to the voltage sampling pin of the main control chip U1, and the control input end of the switch circuit is connected to the control signal output end of the control circuit.

2. The input overvoltage protection circuit of the switching power supply according to claim 1, characterized in that: The switch circuit includes a phototransistor OT1-A of an optical coupler OT1, the collector of the phototransistor OT1-A is connected to the voltage sampling pin of the main control chip U1 as the output end of the switch circuit, the emitter of the phototransistor OT1-A is grounded, and the switch circuit outputs a switch signal to control the main control chip U1 to perform power conversion.

3. The input overvoltage protection circuit of the switching power supply according to claim 2, characterized in that: The voltage sampling circuit includes a voltage divider circuit, which includes a resistor R13, a resistor R14, and a resistor R15. The second end of the resistor R13 is connected to the first end of the resistor R14 and the first end of the resistor R15 in parallel, and the second end of the resistor R14 and the second end of the resistor R15 are grounded to form a voltage divider circuit. The first end of the resistor R13 is the input end of the voltage divider circuit and is connected to the DC bus. The connection point between the second end of the resistor R13 and the first end of the resistor R14 and the first end of the resistor R15 is the output end of the voltage divider circuit. The output end of the voltage divider circuit is connected to the reference electrode of the controllable precision voltage stabilizing source U3.

4. The input overvoltage protection circuit of the switching power supply according to claim 3, characterized in that: The control circuit further includes a first capacitor C7, which is a filter capacitor of the base of the transistor Q1. A first end of the first capacitor C7 is connected to the transistor Q1, and a second end of the first capacitor C7 is grounded.

5. The input overvoltage protection circuit of the switching power supply according to claim 4, characterized in that: The control circuit also includes a second capacitor C10, a third capacitor C44, and a resistor R12. The first end of the third capacitor C44 is connected to the reference electrode of the controllable precision voltage-stabilizing source U3 and the first end of the second capacitor C10. The second end of the third capacitor C44 is connected to the negative electrode of the controllable precision voltage-stabilizing source U3. The capacitor C44 serves as a filter capacitor of the controllable precision voltage-stabilizing source U3. The second capacitor C10 and the resistor R12 are connected in series to form a loop to absorb low-frequency interference at the output end of the voltage divider circuit.

6. The input overvoltage protection circuit of the switching power supply according to claim 1, characterized in that: The negative pole of the controllable precision voltage-stabilizing source U3 of the control circuit is connected to the negative pole of the light-emitting diode OT1-B of the optocoupler OT1, the positive pole of the controllable precision voltage-stabilizing source U3 is grounded, the reference pole of the controllable precision voltage-stabilizing source U3 is the input end of the control circuit, a reference voltage is provided inside the controllable precision voltage-stabilizing source U3, the output voltage of the voltage divider circuit is connected to the reference pole of the controllable precision voltage-stabilizing source U3 and is compared with the reference voltage inside the controllable precision voltage-stabilizing source U3, the control circuit outputs a signal to the input end of the switching circuit, and the optocoupler OT1 of the control switching circuit outputs a control signal.

7. The input overvoltage protection circuit of the switching power supply according to claim 3, characterized in that: The voltage divider circuit also includes a bidirectional diode D16 and a capacitor C40. The first end of the bidirectional diode D16 is connected to the first end of the capacitor C40. The second end of the bidirectional diode D16 is connected to the first end of the resistor R13. The second end of the capacitor C40 is connected to the second end of the resistor R13.

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