WO2019228093A1

WO2019228093A1 - Switch power supply and switch tube protection circuit thereof

Info

Publication number: WO2019228093A1
Application number: PCT/CN2019/083194
Authority: WO
Inventors: 肖钊; 黄小华; 任新杰
Original assignee: 广东美芝制冷设备有限公司
Priority date: 2018-05-30
Filing date: 2019-04-18
Publication date: 2019-12-05
Also published as: CN208158102U

Abstract

Disclosed are a switch power supply and a switch tube protection circuit thereof. The switch tube protection circuit comprises: a detection module for detecting a bus voltage on a bus of a switch power supply, and when the bus voltage is greater than a set bus voltage threshold value, outputting a first control signal, and when the bus voltage is equal to or less than the set bus voltage threshold value, outputting a second control signal; and a control module, connected to the detection module and used for turning off the output of a switch tube when receiving the first control signal, and maintaining the output of the switch tube when receiving the second control signal. The circuit can turn off a switch tube in a switch power supply when overvoltage of the switch power supply occurs, thereby effectively reducing the influence of a bus voltage fluctuation and a power-on surge voltage on the switch power supply, further reducing the failure rate of the switch power supply due to the overvoltage of the switch tube, and improving the reliability of the switch power supply; and the circuit is also low in cost.

Description

Switching power supply and switching tube protection circuit thereof

Cross-reference to related applications

This application claims the priority of Chinese patent application number "201820838986.3", filed by Guangdong Meizhi Refrigeration Equipment Co., Ltd. on May 30, 2018, with the utility model name "Switching Power Supply and Its Switch Tube Protection Circuit".

Technical field

The present application relates to the technical field of analog integrated circuits, and in particular, to a switching tube protection circuit for a switching power supply and a switching power supply.

Background technique

Because of its small size and high efficiency, switching power supplies are widely used in various consumer electronics products. As an essential part of power supplies, switching power supplies use switching tubes to turn on and off and store energy with inductors, and control the duty cycle to adjust The voltage output is divided into step-down and step-up switching power supplies. When the switching power supply is operating, the voltage VDS on the switching tube is the sum of the bus voltage, the output reflected voltage, and the voltage caused by the leakage inductance.

At present, due to the different voltage fluctuations of various types of power grids and the impact of power-on surge voltages, it is not uncommon to see burned out switching tubes of switching power supplies. In order to solve this problem, in the related art, a high-withstand voltage switch tube is generally used, but this method will greatly increase the cost of the switching power supply.

Application content

This application aims to solve at least one of the technical problems in the above-mentioned technologies. To this end, an object of the present application is to provide a switching tube protection circuit for a switching power supply, which can turn off the switching tube in the switching power supply when an overvoltage occurs in the switching power supply, effectively reducing the voltage fluctuation and The impact of the power-on surge voltage on the switching power supply further reduces the failure rate of the switching power supply due to the overvoltage of the switching tube, improves the reliability of the switching power supply, and has a lower cost.

Another object of the present application is to propose a switching power supply.

In order to achieve the above object, on the one hand, the present application proposes a switching tube protection circuit for a switching power supply, including: a detection module and a control module connected to the detection module; and the detection module is used to detect a bus of the switching power supply. The bus voltage on the bus is greater than the set bus voltage threshold and outputs a first control signal; the bus voltage is equal to or less than the set bus voltage threshold and outputs a second control signal; the control module is configured to: When the first control signal is received, the output of the switch is turned off; when the second control signal is received, the output of the switch is maintained.

According to the switching tube protection circuit of the switching power supply of the present application, the detection module detects a bus voltage of the switching power supply, the bus voltage is greater than a set bus voltage threshold, and outputs a first control signal, the bus voltage is equal to or less than the set bus voltage threshold, and outputs a second The control signal, the control module receives the first control signal, turns off the output of the switch tube, receives the second control signal, and maintains the output of the switch tube. Therefore, the circuit can turn off the switching tube in the switching power supply when the switching power supply is over-voltage, effectively reducing the influence of the bus voltage fluctuation and the power-on shock voltage on the switching power supply, thereby reducing the switching power supply factor. The failure rate caused by the overvoltage of the switching tube improves the reliability of the switching power supply and the cost is lower.

In addition, the switch protection circuit of the switching power supply according to the above application may also have the following additional technical features:

Specifically, the detection module includes: a voltage division sampling unit and a comparison unit connected to the voltage division sampling unit, the comparison unit being connected to the control module; and a voltage division sampling unit for The bus voltage is divided, and the divided bus voltage is sampled. A comparison unit is configured to compare the divided voltage with the set bus voltage division threshold. If the voltage of the bus bar after the voltage is greater than the set bus voltage voltage division threshold, it is determined that the bus voltage is greater than the set bus voltage threshold value, and the first control signal is output; if the divided bus voltage Is equal to or less than the set bus voltage voltage division threshold, it is determined that the bus voltage is equal to or less than the set bus voltage threshold, and the second control signal is output.

Specifically, the control module includes a control unit and a driving unit connected to the control unit, the control unit is connected to the detection module, and the control unit is configured to receive the first control signal and output A first driving control signal; receiving the second control signal and outputting a second driving control signal; the driving unit for receiving the first driving control signal, outputting the first driving signal, and turning off the switch Output of the tube; receiving the second driving control signal, outputting the second driving signal, and maintaining the output of the switching tube.

Further, the voltage dividing sampling unit includes: a first voltage dividing resistor and a second voltage dividing resistor; a first end of the first voltage dividing resistor is connected to a bus of the switching power supply, and the first voltage dividing resistor The second end of the second voltage-dividing resistor is connected to the first end of the second voltage-dividing resistor, and the second end of the second voltage-dividing resistor is grounded; The output is a positive terminal, and the second terminal of the second voltage dividing resistor is used as an output negative terminal of the voltage dividing sampling unit.

Specifically, the voltage dividing sampling unit further includes: a filtering capacitor; a first end of the filtering capacitor is connected to a first end of the second voltage dividing resistor, and a second end of the filtering capacitor is connected to the second The second end of the voltage dividing resistor is connected.

Specifically, the comparison unit is a comparator; a reference pin of the comparator is connected to a first terminal of the second voltage dividing resistor, and a cathode pin of the comparator is used as an output terminal of the comparison unit. The anode of the comparator is grounded.

Specifically, the control unit includes: a PNP-type transistor and an NPN-type transistor; a base of the PNP-type transistor is connected to a cathode pin of the comparator, an emitter of the PNP-type transistor and a built-in of the switching power supply The power source is connected, the collector of the PNP transistor is connected to the base of the NPN transistor, the emitter of the NPN transistor is grounded, and the collector of the NPN transistor is used as an output terminal of the control unit.

Further, the control unit further includes a third voltage-dividing resistor, a fourth voltage-dividing resistor, and a fifth voltage-dividing resistor; a first end of the fourth voltage-dividing resistor is connected to a built-in power source of the switching power supply, and The second end of the fourth voltage-dividing resistor is connected to the emitter of the PNP-type transistor; the first end of the third voltage-dividing resistor is connected to the emitter of the PNP-type transistor, and the third voltage-dividing resistor The second end of the PNP-type transistor is connected to the base; the first end of the fifth voltage-dividing resistor is connected to the collector of the PNP-type transistor; the second end of the fifth voltage-dividing resistor is connected to the Base connection of NPN triode.

To achieve the above object, the second aspect of the present application proposes a switching power supply, which includes a switching tube and the switching tube protection circuit according to the embodiment of the first aspect of the application. The control module in the switching tube protection circuit and the Switch tube connection.

According to the switching power supply of the present application, through the above-mentioned switching tube protection circuit, the switching tube in the switching power supply can be turned off when the switching power supply is over-voltage, which effectively reduces the switching power supply caused by bus voltage fluctuations and power surge voltage. The influence of the switching power supply reduces the failure rate of the switching power supply due to the overvoltage of the switching tube, improves the reliability of the switching power supply, and has a lower cost.

In addition, the switching power supply proposed above according to this application may also have the following additional technical features:

Specifically, the above-mentioned switching power supply further includes: a bus bar; a detection module in the switch tube protection circuit is connected to the bus bar.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and / or additional aspects and advantages of the present application will become apparent and easy to understand from the following description of the embodiments with reference to the accompanying drawings, in which,

FIG. 1 is a block diagram of a switch protection circuit of a switching power supply according to an embodiment of the present application; FIG.

2 is a schematic block diagram of a switch protection circuit of a switching power supply according to another embodiment of the present application;

3 is a circuit topology diagram of a switching tube protection circuit of a switching power supply according to an embodiment of the present application;

FIG. 4 is a block diagram of a switching power supply according to an embodiment of the present application.

Detailed ways

Hereinafter, embodiments of the present application are described in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary, and are intended to explain the present application, and should not be construed as limiting the present application.

The following describes the switching tube protection circuit and the switching power supply of the switching power supply according to the embodiments of the present application with reference to the accompanying drawings.

FIG. 1 is a block diagram of a switch protection circuit of a switching power supply according to an embodiment of the present application. As shown in FIG. 1, the protection circuit includes a detection module 10 and a control module 20.

The detection module 10 is configured to detect a bus voltage VDC on the bus of the switching power supply. The bus voltage VDC is greater than a set bus voltage threshold and outputs a first control signal; the bus voltage VDC is equal to or less than the set bus voltage threshold and outputs a second control signal. The control module 20 is configured to receive the first control signal and turn off the output of the switch; and receive the second control signal to maintain the output of the switch. The setting of the bus voltage threshold can be preset according to the withstand voltage parameters of the switching tube.

Specifically, the control module 20 can adjust the pulse width or pulse frequency of a PWM (Pulse Width Modulation) signal that drives the switching tube to make the switching power supply output stably. The detection module 10 detects the bus voltage VDC of the switching power supply, and generates a control signal according to the bus voltage VDC. Among them, if the bus voltage VDC is higher than the set bus voltage threshold due to grid fluctuations or power-on surge voltage, etc., the detection module 10 outputs the first A control signal, the control module 20 receives the first control signal, and turns off the output of the switch tube, that is, turns off the PWM signal input to the switch tube to protect the switch tube and prevent the switch tube from being damaged due to overvoltage. If the bus voltage VDC is less than or equal to the set bus voltage threshold, the detection module 10 generates a second detection signal, the control module 20 controls the module 20 to receive the second control signal, determines that the bus voltage is normal, maintains the output of the switching tube, and the switching power supply is normal jobs. This circuit can turn off the switching tube in the switching power supply when the switching power supply is over-voltage, effectively reducing the influence of the bus voltage fluctuation and power-on surge voltage on the switching power supply, thereby reducing the switching power supply due to the switching tube The failure rate caused by the voltage improves the reliability of the switching power supply and the cost is lower.

Further, in the embodiment of the present application, as shown in FIG. 2, the detection module 10 may include: a voltage division sampling unit 101 and a comparison unit 102. The comparison unit 102 is connected to the voltage-dividing sampling unit 101, and the comparison unit 102 is connected to the control module 20. The voltage dividing and sampling unit 101 is configured to divide the voltage of the bus voltage VDC of the switching power supply, and sample the divided bus voltage. A comparison unit for comparing the divided bus voltage with a set bus voltage division threshold, and if the divided bus voltage is greater than the set bus voltage division threshold, determining that the bus voltage is greater than the set bus voltage threshold, A first control signal is output; if the divided bus voltage is equal to or less than a set bus voltage division threshold, it is determined that the bus voltage is equal to or less than a set bus voltage threshold, and a second control signal is output. The voltage threshold of the bus voltage can be preset according to the withstand voltage of the switch.

Specifically, as shown in FIG. 2, the voltage dividing and sampling unit 101 may divide the voltage of the bus voltage VDC of the switching power supply, and send the divided bus voltage to the comparison unit 102. The comparison unit 102 outputs a corresponding control signal according to the divided bus voltage. Among them, if the divided bus voltage is greater than the divided threshold voltage of the bus voltage, indicating that the bus voltage may be over-voltage, the comparison unit 102 outputs a first control signal; if the divided bus voltage is less than or equal to the divided voltage threshold of the bus voltage, it indicates that The bus voltage is normal, and the comparison unit 102 outputs a second control signal.

According to an embodiment of the present application, as shown in FIG. 2, the control module 20 may include a control unit 201 and a driving unit 202. The control unit 201 is connected to the driving unit 202, and the control unit is connected to the 201 detection module 10. The control unit 201 is configured to receive a first control signal and output a first driving control signal; and receive a second control signal to output a second driving control signal. The driving unit 202 is configured to receive the first driving control signal, output the first driving signal, and turn off the output of the switching tube; receive the second driving control signal, output the second driving signal, and maintain the output of the switching tube.

Specifically, the driving unit 201 is configured to output a driving signal (for example, a PWM signal) to the switching transistor to drive the switching transistor on / off. As shown in FIG. 2, if the divided bus voltage is greater than the bus voltage division threshold, it indicates that the bus voltage may be over-voltage. The comparison unit 102 outputs a first control signal to the control unit 201. The first driving control signal is output to the driving unit 202 under the control. The driving unit 202 outputs the first driving signal to the switching tube under the control of the first driving control signal. The switching tube is turned off under the control of the first driving signal to avoid overshooting. Pressure damage. If the divided bus voltage is less than or equal to the bus voltage division threshold, the bus voltage is normal, the comparison unit 102 outputs a second control signal to the control unit 201, and the control unit 201 outputs a second drive control under the control of the second control signal. The signal is sent to the driving unit 202. The driving unit 202 outputs a second driving signal to the switching tube under the control of the second driving control signal. The switching tube keeps outputting under the control of the second driving signal, and the switching power supply works normally. Therefore, the influence of the bus voltage fluctuation and the power-on surge voltage on the switching power supply is reduced, thereby reducing the failure rate of the switching power supply due to the overvoltage of the switching tube, improving the reliability of the switching power supply, and lowering the cost.

The specific circuit topology of the switch protection circuit is described below with specific examples.

According to an embodiment of the present application, as shown in FIG. 3, the voltage dividing sampling unit 101 may include a first voltage dividing resistor R1 and a second voltage dividing resistor R2. The first terminal of the first voltage dividing resistor R1 is connected to the bus of the switching power supply, the second terminal of the first voltage dividing resistor R1 is connected to the first terminal of the second voltage dividing resistor R2, and the first terminal of the second voltage dividing resistor R2 is connected. Ground at both ends. The first terminal of the second voltage dividing resistor R2 is used as the output positive terminal of the voltage dividing sampling unit 101, and the second terminal of the second voltage dividing resistor R2 is used as the output negative terminal of the voltage dividing sampling unit 101.

Further, as shown in FIG. 3, the voltage-dividing sampling unit 101 may further include a filter capacitor C1. The first terminal of the filter capacitor C1 is connected to the first terminal of the second voltage dividing resistor R2, and the second terminal of the filter capacitor C1 is connected to the second terminal of the second voltage dividing resistor R2.

Specifically, the voltage-dividing sampling unit 101 may divide the bus voltage, and send the divided bus voltage to the comparison unit 102 through the output positive terminal. The filtering capacitor C1 can perform filtering processing on the divided bus voltage. The divided bus voltage output by the divided voltage sampling unit 101 is

Therefore, if the bus voltage fluctuates, the divided bus voltage output by the voltage-dividing sampling unit 101 will also fluctuate accordingly.

According to an embodiment of the present application, as shown in FIG. 3, the comparison unit 102 is a comparator; the reference pin of the comparator is connected to the first end of the second voltage dividing resistor R2, and the cathode pin of the comparator is used as the output of the comparison unit 102. The anode of the comparator is grounded.

Specifically, the comparator may be a chip TL431, and the internal reference voltage Vref may be set to 2.5V. When the voltage of the reference pin of the comparator is greater than the internal reference voltage Vref, the anode pin and the cathode pin of the comparator are turned on. When the voltage of the reference pin of the comparator is less than the internal reference voltage Vref, the comparator is turned off.

According to an embodiment of the present application, as shown in FIG. 3, the control unit 201 may include a PNP-type transistor Q1 and an NPN-type transistor Q2. The base of PNP transistor Q1 is connected to the cathode of the comparator. The emitter of PNP transistor Q1 is connected to the built-in power supply VDD of the switching power supply. The collector of PNP transistor Q1 is connected to the base of NPN transistor Q2. NPN The emitter of the transistor Q2 is grounded, and the collector of the NPN transistor Q2 is used as the output terminal of the control unit 201.

Further, as shown in FIG. 3, the control unit 201 may further include a third voltage dividing resistor R3, a fourth voltage dividing resistor R4, and a fifth voltage dividing resistor R5. The first terminal of the fourth voltage dividing resistor R4 is connected to the built-in power supply VDD of the switching power supply, and the second terminal of the fourth voltage dividing resistor R4 is connected to the emitter of the PNP transistor Q1; the first of the third voltage dividing resistor R3 Is connected to the emitter of PNP transistor Q1, the base of PNP transistor Q1 is connected to the second terminal of the third voltage dividing resistor R3; the first end of fifth resistor R5 is connected to the collector of PNP transistor Q1, The second end of the fifth voltage dividing resistor R5 is connected to the base of the NPN transistor Q2.

Specifically, as shown in FIG. 3, the voltage-dividing sampling unit 101 may divide the bus voltage, and send the divided bus voltage to the reference pin of the comparator through the positive output terminal. If the divided bus voltage is greater than the internal reference voltage Vref of the comparator, the anode and cathode pins of the comparator are turned on, and the emitter and base of Q1 generate a 0.7V voltage drop, Q1 is turned on, and Q1 is set. The electrode drives the transistor Q2 to be turned on through R5. After Q2 is turned on, the driving unit 202 stops outputting the PWM signal to the switching tube. At this time, the voltage of the switching tube does not superimpose the voltage caused by the reflected voltage and the leakage inductance. If the voltage of the bus after voltage is less than the internal reference voltage Vref of the comparator, the comparator is turned off, Q1 and Q2 are turned off, the driving unit 202 keeps the output of the switching tube, and the switching power supply works normally. Therefore, the influence of the bus voltage fluctuation and the power-on surge voltage on the switching power supply is reduced, thereby reducing the failure rate of the switching power supply due to the overvoltage of the switching tube, improving the reliability of the switching power supply, and lowering the cost.

In summary, according to the switching tube protection circuit of the switching power supply of the present application, the detection module detects the bus voltage of the switching power supply. When the bus voltage is greater than a set bus voltage threshold, a first control signal is output. When the bus voltage threshold is fixed, the second control signal is output. When the control module receives the first control signal, the output of the switch is turned off. When the second control signal is received, the output of the switch is maintained. Therefore, the circuit can turn off the switching tube in the switching power supply when the switching power supply is over-voltage, effectively reducing the influence of the bus voltage fluctuation and the power-on shock voltage on the switching power supply, thereby reducing the switching power supply factor. The failure rate caused by the overvoltage of the switching tube improves the reliability of the switching power supply and the cost is lower.

In addition, as shown in FIG. 4, the present application also proposes a switching power supply 100 including a switching tube 101 and the above-mentioned switching tube protection circuit 102. The control module 20 in the switching tube protection circuit 102 is connected to the switching tube 101. The switching power supply 100 further includes: a bus bar L; the detection module 10 in the switch protection circuit 102 is connected to the bus bar L.

In the description of this application, it should be understood that the terms “first” and “second” are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality" is two or more, unless it is specifically and specifically defined otherwise.

In this application, the terms "installation," "connected," "connected," and "fixed" should be understood broadly unless otherwise specified and limited, for example, they may be fixed connections or removable connections Or integrated; it can be mechanical or electrical; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

In this application, unless explicitly stated and limited otherwise, the first feature "on" or "down" of the second feature may be the first and second features in direct contact, or the first and second features indirectly through an intermediate medium. contact. Moreover, the first feature is "above", "above", and "above" the second feature. The first feature is directly above or obliquely above the second feature, or it only indicates that the first feature is higher in level than the second feature. The first feature is “below”, “below”, and “below” of the second feature. The first feature may be directly below or obliquely below the second feature, or it may simply indicate that the first feature is less horizontal than the second feature.

In the description of this specification, the description with reference to the terms “one embodiment”, “some embodiments”, “examples”, “specific examples”, or “some examples” and the like means specific features described in conjunction with the embodiments or examples , Structure, materials, or features are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, without any contradiction, those skilled in the art may combine and combine different embodiments or examples and features of the different embodiments or examples described in this specification.

Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations on the present application. Those skilled in the art can interpret the above within the scope of the present application. Embodiments are subject to change, modification, substitution, and modification.

Claims

A switching tube protection circuit for a switching power supply, comprising: a detection module and a control module connected to the detection module;

The detection module is configured to detect a bus voltage on a bus of the switching power supply, the bus voltage being greater than a set bus voltage threshold, and outputting a first control signal; the bus voltage being equal to or less than the set bus voltage threshold To output a second control signal;

The control module is configured to receive the first control signal and turn off the output of the switch tube; and receive the second control signal and maintain the output of the switch tube.
The switch protection circuit according to claim 1, wherein the detection module comprises: a voltage division sampling unit and a comparison unit connected to the voltage division sampling unit, and the comparison unit is connected to the control module;

A voltage dividing and sampling unit, configured to divide the voltage of the bus voltage of the switching power supply, and sample the voltage of the bus voltage after the voltage division;

A comparison unit is configured to compare the bus voltage after the voltage division with a set bus voltage voltage division threshold. If the voltage after the voltage division is greater than the set bus voltage voltage division threshold, then Determine that the bus voltage is greater than the set bus voltage threshold, and output the first control signal; if the divided bus voltage is equal to or less than the set bus voltage division threshold, determine the bus voltage Is equal to or less than the set bus voltage threshold, and outputs the second control signal.
The switch protection circuit according to claim 2, wherein the control module comprises: a control unit and a drive unit connected to the control unit, and the control unit is connected to the detection module;

The control unit is configured to receive the first control signal and output a first drive control signal; receive the second control signal and output a second drive control signal;

The driving unit is configured to receive the first driving control signal, output the first driving signal, and turn off the output of the switching tube; receive the second driving control signal, output the second driving signal, and maintain the The output of the switch is described.
The switch protection circuit according to claim 3, wherein the voltage-dividing sampling unit comprises: a first voltage-dividing resistor and a second voltage-dividing resistor;

A first terminal of the first voltage dividing resistor is connected to a bus of the switching power supply, a second terminal of the first voltage dividing resistor is connected to a first terminal of the second voltage dividing resistor, and the second voltage dividing resistor The second end of the varistor is grounded;

A first terminal of the second voltage dividing resistor is used as an output positive terminal of the voltage dividing sampling unit, and a second terminal of the second voltage dividing resistor is used as an output negative terminal of the voltage dividing sampling unit.
The switch protection circuit according to claim 4, wherein the voltage-dividing sampling unit further comprises: a filter capacitor;

A first terminal of the filter capacitor is connected to a first terminal of the second voltage dividing resistor, and a second terminal of the filter capacitor is connected to a second terminal of the second voltage dividing resistor.
The switch protection circuit according to claim 4, wherein the comparison unit is a comparator;

A reference pin of the comparator is connected to a first end of the second voltage dividing resistor, a cathode pin of the comparator is used as an output terminal of the comparison unit, and an anode pin of the comparator is grounded.
The switch protection circuit according to claim 6, wherein the control unit comprises: a PNP-type transistor and an NPN-type transistor;

The base of the PNP transistor is connected to the cathode pin of the comparator, the emitter of the PNP transistor is connected to the built-in power supply of the switching power supply, and the collector of the PNP transistor is connected to the NPN transistor. The base of the NPN triode is connected to ground, and the collector of the NPN triode is used as the output terminal of the control unit.
The switch protection circuit according to claim 7, wherein the control unit further comprises: a third voltage-dividing resistor, a fourth voltage-dividing resistor, and a fifth voltage-dividing resistor;

A first end of the fourth voltage dividing resistor is connected to a built-in power source of the switching power supply, and a second end of the fourth voltage dividing resistor is connected to an emitter of the PNP transistor;

A first end of the third voltage-dividing resistor is connected to an emitter of the PNP-type transistor, and a second end of the third voltage-dividing resistor is connected to a base of the PNP-type transistor;

A first end of the fifth voltage-dividing resistor is connected to a collector of the PNP-type transistor, and a second end of the fifth voltage-dividing resistor is connected to a base of the NPN-type transistor.
A switching power supply, comprising a switching tube and the switching tube protection circuit according to any one of claims 1-8;

A control module in the switch protection circuit is connected to the switch.
The switching power supply according to claim 9, further comprising: a bus bar;

A detection module in the switch protection circuit is connected to the bus.