Silicon controlled rectifier-based protection circuit and switching power supply

Through the Thyristor-based protection circuit, the hysteresis comparator and relay are used to achieve rapid protection of the switching power supply, solving the problem of output instability caused by grid fluctuations, reducing costs and improving the reliability of the power supply.

CN223052745UActive Publication Date: 2025-07-01江苏神州半导体科技股份有限公司
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Patent Information

Application Number
CN202421749271.2
Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
Filing Date
2024-07-23
Publication Date
2025-07-01
Estimated Expiration
2034-07-23

AI Technical Summary

Technical Problem

Switching power supplies are sensitive to grid fluctuations, which can easily lead to unstable outputs, and the existing protection circuits are costly, making it difficult to effectively prevent failures.

Method used

Thyristor-based protection circuits are adopted, including Thyristor modules, soft start circuits, Thyristor-controlled driving circuits, input detection circuits and output detection circuits, and a protection mechanism with fast response is achieved through hysteresis comparators and relays.

Benefits of technology

Effectively prevent the output voltage changes caused by power grid fluctuations, quickly cut off the faulty circuit, protect the subsequent circuit, low cost and quick response.

✦ Generated by Eureka AI based on patent content.

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Abstract

The utility model discloses a silicon controlled rectifier-based protection circuit and a switching power supply. The protection circuit comprises a silicon controlled rectifier module, a soft start circuit, a silicon controlled rectifier drive circuit, an input detection circuit and an output detection circuit, wherein the silicon controlled rectifier module is electrically connected with the soft start circuit, the silicon controlled rectifier drive circuit, the input detection circuit and the output detection circuit are connected through diodes D1 and D2, and the silicon controlled rectifier module is connected with the silicon controlled rectifier drive circuit through a relay K1. The switching power supply comprises a main circuit, a control and auxiliary circuit and the protection circuit. According to the utility model, stable and adjustable output voltage is realized by utilizing the characteristics of on-off of the high-frequency switching tube and energy storage of the inductor.
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Description

Technical Field

[0001] The utility model relates to the technical field of circuit structures, and particularly relates to a switching power supply protection circuit based on a thyristor. Background Art

[0002] A switching power supply is a high-frequency power conversion device that can convert one form of electrical energy into another. Its input is mostly an AC power supply, and its output is mostly a DC power supply. The main principle is to utilize the on-off of high-frequency switching tubes and the characteristics of inductive energy storage to achieve a stable and adjustable output voltage. It is widely used in industrial manufacturing, medical equipment, solar energy and other fields.

[0003] The switching power supply mainly consists of a main circuit (common topologies of switching power supplies such as BUCK, BOOST, and BUCK - BOOST), a control circuit (composed of an error amplifier, a pulse width modulator PWM, a current amplifier, etc., whose main function is to sample the output terminal, compare it with the set value, and then adjust the pulse width to stabilize the output voltage), and an auxiliary circuit (mainly the auxiliary power supply for the detection circuit).

[0004] Its working principle is as follows: After the input is rectified and filtered, direct current is obtained. Then, a power device is used as a switch to perform periodic on-off, converting the input voltage into high-frequency pulses. Finally, through the output filter capacitor, a relatively stable DC voltage is output.

[0005] The advantages of the switching power supply are obvious. Due to its high-frequency characteristics, the key internal components work in a high-frequency switching state, so it has characteristics such as high efficiency and high stability. At the same time, compared with linear power supplies, it also has advantages such as a lighter volume and weight.

[0006] The switching power supply currently still has the following deficiencies: The cost of MOSFET devices is relatively high; the high working frequency causes spike voltages and currents to be generated during the switching process, resulting in relatively large electromagnetic interference. It is sensitive to grid fluctuations, and relatively large grid fluctuations may cause the output of the switching voltage to be unstable, and in severe cases, it may even lead to the failure of the switching power supply. Therefore, a low-cost protection circuit is needed to monitor the input and output of the switching power supply. Summary of the Invention

[0007] To achieve the above object, the utility model provides a switching power supply protection circuit based on a thyristor, providing a new solution for the switching power supply:

[0008] A protection circuit based on a thyristor includes: a thyristor module, a soft start circuit, a thyristor drive circuit, an input detection circuit, and an output detection circuit;

[0009] Among them, the thyristor module and the input end of the soft start circuit are simultaneously connected to three-phase alternating current. The thyristor drive circuit, the input detection circuit, and the output detection circuit are connected through diodes D1 and D2. The thyristor module and the thyristor drive circuit are connected through relay K1.

[0010] Further, the thyristor module is a three-phase bridge semi-controlled rectifier circuit. The three-phase alternating current is respectively connected to input pins 4, 5, and 6 of the thyristor module. The control pins 1, 2, and 3 of the thyristor module are connected to relay K1 in the thyristor drive circuit. The output pins of the thyristor module are 7 and 8, where pin 7 is connected to GND-2.

[0011] Further, in the thyristor drive circuit, diodes D1 and D2 are used for clamping. The cathode of diode D1 is connected to the output signal of the output detection circuit, and the cathode of D2 is connected to the output signal of the input detection circuit. The anodes of diodes D1 and D2 are both connected to the base of NPN transistor Q2; resistor R5 is a pull-up resistor, one end is connected to power supply VCC, and the other end is connected to the base of Q2; R6 is a pull-down resistor, one end is connected to GND, and the other end is connected to the base of Q2; resistors R7 and R22 are both current-limiting resistors. One end of R7 is connected to VCC, and the other end is connected to the collector of Q2. One end of R22 is connected to VCC, and the other end is connected to the collector of Q5; the emitters of NPN transistors Q5 and Q2 are both connected to GND. The base of Q5 is connected to the collector of Q2. Q2 and Q5 play the role of making the input and output signals in the same phase; the anode of diode D4 is connected to the collector of Q5, and the cathode is connected to the gate of N-type MOS (Q4); one end of capacitor C3 is connected to the gate of Q4, and the other end is connected to GND; C3 and D4 form a peak detection circuit to detect and hold the maximum value of the input; resistor R12 is a discharge pull-down resistor, one end is connected to the gate of Q4, and the other end is connected to GND; the drain of Q4 is connected to pin 2 of optocoupler U3, and the source is connected to GND; resistor R10 is a current-limiting resistor, one end is connected to VCC, and the other end is connected to pin 1 of U3; resistor R9 is a current-limiting resistor, one end is connected to VCC-1, and the other end is connected to pin 4 of U3; resistor R24 is the base resistor of Q3, one end is connected to pin 3 of U3, and the other end is connected to the base of Q3; R8 is a pull-down resistor, one end is connected to the base of Q3, and the other end is connected to GND-1; the emitter of NPN transistor Q3 is connected to GND-1, and the collector is connected to pin 1 of K1; pin 3 of relay K1 is connected to VCC-2, and pin 4 is connected to VCC-1; D5 is a freewheeling diode for the relay coil, the cathode is connected to pin 4 of K1, and the anode is connected to pin 1 of K1.

[0012] Furthermore, the input detection circuit includes a hysteresis comparator U1.1; one end of the resistor R1 is connected to Vin, and the other end is connected to the non-inverting input terminal of U1.1, one end of R2 is connected to GND, and the other end is connected to the non-inverting input terminal of U1.1, and the inverting input terminal of U1.1 is connected to Vref-1; the resistor R3 is a positive feedback resistor, one end of R3 is connected to the output terminal of U1.1, and the other end is connected to the non-inverting input terminal of U1.1; R4 is a pull-up resistor, one end of which is connected to VCC, and the other end is connected to the output terminal of U1.1; R23 and LED2 constitute an input indication circuit, one end of R23 is connected to GND, and the other end is connected to the cathode of LED2, and the anode of LED2 is connected to the output terminal of U1.1.

[0013] Furthermore, the output detection circuit includes two comparators U2.1 and U1.2; one end of resistor R20 is connected to Vbus and the other end is connected to the inverting input of U2.1; one end of R21 is connected to GND and the other end is connected to the inverting input of U2.1; the non-inverting input of U2.1 is connected to Vref-2; the output of U2.1 is connected to the non-inverting input of U1.2; resistors R17 and R15 act as voltage dividers; one end of R17 is connected to VCC and the other end is connected to the non-inverting input of U1.2; one end of R15 is connected to GND and the other end is connected to the non-inverting input of U1.2 The inverting input of U1.2 is connected to Vref-3; resistor R14 is a positive feedback resistor, one end of R14 is connected to the output of U1.2, and the other end is connected to the non-inverting input of U1.2; R16 is a pull-up resistor to prevent an open drain state when the output is high, one end of which is connected to VCC, and the other end is connected to the output of U1.2; U1.2 is a hysteresis comparator, which can suppress noise and glitches; R13 and LED1 constitute an output indication circuit, one end of R13 is connected to VCC, and the other end is connected to the anode of LED1, and the cathode of LED1 is connected to the output of U1.2.

[0014] Furthermore, the input detection circuit comprises:

[0015] When the output is high, the rising threshold is Uth; when the output is low, the falling threshold is Utl;

[0016] When the input of U1.1 satisfies that Vref-1 is greater than Uth, the output of U1.1 flips and becomes a low level. When the input of U1.1 satisfies that Vref-1 is less than Utl, the output of U1.1 flips and becomes a high level. When it is a high level, LED2 lights up, indicating that Vin meets the turn-on threshold. At this time, there is no input at the inverting input of U2.1, and U2.1 outputs a high level. The non-inverting input of U1.2 must be greater than the inverting input of U1.2, and U1.2 outputs a high level. D1 and D2 are both reversely cut off, and the main circuit starts to run.

[0017] Furthermore, the output detection circuit comprises:

[0018] When the output is at a high level, the threshold rising threshold is Uth1 at this time; when the output is at a low level, the threshold falling threshold is Utl1 at this time;

[0019] Among them, when the input terminal value of U1.2 satisfies that Vref - 3 is greater than Uth1, the output of U1.2 flips and becomes a low level. When the input terminal of U1.2 satisfies that Vref - 3 is less than Utl1, the output of U1.2 flips and becomes a high level;

[0020] Under normal working conditions, D1 and D2 are both non - conducting, Q2 is saturated and conducting, there is no voltage input to the base of Q5, Q5 is non - conducting, the output is at a high level. Through the gate of Q4, Q4 is conducting, the 2 - pin of U3 is connected to GND, then U3 is conducting, Q3 is saturated and conducting, the 1 - pin of relay K1 is connected to GND - 1, the relay is attracted, the thyristor meets the turn - on condition, and the circuit works normally.

[0021] A switching power supply based on a thyristor, comprising a main circuit, a control and auxiliary circuit, and the protection circuit described above;

[0022] Among them, Vin and GND of the main circuit are connected to Vin and GND of the thyristor module and the soft - start circuit in the protection circuit. The output Vbus and Vin of the main circuit are respectively connected to the output detection circuit and the input detection circuit. The main circuit is connected to the sampling resistor in the output detection circuit in the protection circuit through the control and auxiliary circuit.

[0023] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0024] 1. The protection circuit proposed by the present utility model can effectively prevent the output voltage change caused by power grid fluctuations, and can quickly cut off the faulty circuit to protect the subsequent circuit from being affected and avoid unnecessary losses.

[0025] 2. The protection circuit proposed by the present utility model has a fast response and a low cost. Description of the Drawings

[0026] By reading the detailed description of the non - restrictive embodiments with reference to the following drawings, other features, purposes and advantages of the present utility model will become more obvious:

[0027] Figure 1 It is a schematic connection diagram of the switching power supply and the protection circuit of the embodiment of the present utility model;

[0028] Figure 2 It is a schematic diagram of the circuit module of the embodiment of the present utility model;

[0029] Figure 3 It is a connection diagram of the circuit modules of the embodiment of the present utility model.

[0030] Figure 2 Description of main components: Soft start circuit - 10, thyristor module - 20, thyristor drive circuit - 30, main circuit - 40, control and auxiliary circuit - 50, input detection circuit - 60, output detection circuit - 70. Specific embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present utility model clearer, the present utility model will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] As Figure 1-2 shown, the thyristor-based switching power supply and protection circuit of the present utility model includes:

[0033] The protection circuit includes: a thyristor module, a soft start circuit, a thyristor drive circuit, an input detection circuit and an output detection circuit; the switching power supply includes: a main circuit, a control and auxiliary circuit.

[0034] Three-phase alternating current first passes through the soft start circuit and then reaches the input end of the main circuit. The input detection circuit detects whether the input voltage reaches the opening threshold. If it is satisfied, the thyristor is turned on and the main circuit starts to work. The main circuit outputs the Vbus voltage at the output end, and the output detection circuit starts to work to detect whether the output Vbus value meets the requirements. If it does not meet the requirements, the thyristor is cut off, and the thyristor will turn off in the negative half cycle of the alternating current and the circuit stops running.

[0035] The thyristor module SCR1 is a three-phase bridge semi-controlled rectifier circuit. The three-phase alternating current is respectively connected to the input pins 4, 5, and 6 of SCR1. The three control poles of SCR1, pins 1, 2, and 3, are connected to the 2nd pin of the relay. The output pins 7, 8 of SCR1, that is, the input voltage Vin of the main circuit, and pin 7 is also connected to GND - 2 at the same time.

[0036] As Figure 3 shown, in the main circuit, the Vin and GND of the thyristor module and the soft start circuit are connected to the Vin and GND of the main circuit. The output Vbus and Vin of the main circuit are respectively connected to the output detection circuit and the input detection circuit. The main circuit is connected to the sampling resistor in the output detection circuit through the control circuit and the auxiliary circuit;

[0037] Among them, the control circuit includes: an error amplifier, a pulse width modulator PWM and a current amplifier, which are used to sample the output end, compare with the set value and then adjust the pulse width to stabilize the output voltage; the auxiliary circuit provides auxiliary power for the detection and drive circuit.

[0038] As Figure 3As shown in the figure, in the thyristor drive circuit: Diodes D1 and D2 both play a clamping role. The cathode of diode D1 is connected to the output signal of the output detection circuit (i.e., pin 7 of comparator U1.2), and the cathode of D2 is connected to the output signal of the input detection circuit (i.e., pin 1 of comparator U1.1). Their anodes are both connected to the base of NPN transistor Q2. Resistor R5 is a pull-up resistor, with one end connected to power supply VCC and the other end connected to the base of Q2. R6 is a pull-down resistor, with one end connected to GND and the other end connected to the base of Q2. Resistors R7 and R22 are both current-limiting resistors. One end of R7 is connected to VCC and the other end is connected to the collector of Q2. One end of R22 is connected to VCC and the other end is connected to the collector of Q5. The emitters of NPN transistors Q5 and Q2 are both connected to GND, and the base of Q5 is connected to the collector of Q2. Q2 and Q5 achieve the function of making the input and output signals in the same phase (i.e., the input at the base of Q2 and the output at the collector of Q5 are in phase). The anode of diode D4 is connected to the collector of Q5, and the cathode is connected to the gate of N-type MOS (Q4). One end of capacitor C3 is connected to the gate of Q4 and the other end is connected to GND. C3 and D4 form a peak detection circuit to detect and hold the maximum value of the input. Resistor R12 is a discharge pull-down resistor, with one end connected to the gate of Q4 and the other end connected to GND. The drain of Q4 is connected to pin 2 of optocoupler U3, and the source is connected to GND. Resistor R10 is a current-limiting resistor, with one end connected to VCC and the other end connected to pin 1 of U3. Resistor R9 has the same function as R10, with one end connected to VCC-1 and the other end connected to pin 4 of U3. Resistor R24 is the base resistor of Q3, with one end connected to pin 3 of U3 and the other end connected to the base of Q3. R8 has the same function as R6, with one end connected to the base of Q3 and the other end connected to GND-1. The emitter of NPN transistor Q3 is connected to GND-1, and the collector is connected to pin 1 of K1. Pin 3 of relay K1 is connected to VCC-2, pin 4 is connected to VCC-1, and D5 is the freewheeling diode of the relay coil, with its cathode connected to pin 4 of K1 and its anode connected to pin 1 of K1.

[0039] The output detection circuit mainly consists of two comparators U2.1 and U1.2: resistors R20 and R21 form a sampling circuit, one end of R20 is connected to Vbus, and the other end is connected to the inverting input of U2.1, one end of R21 is connected to GND, and the other end is connected to the inverting input of U2.1, the non-inverting input of U2.1 is connected to Vref-2, and the output of U2.1 is connected to the non-inverting input of U1.2. Resistors R17 and R15 act as voltage dividers, one end of R17 is connected to VCC, and the other end is connected to the non-inverting input of U1.2, one end of R15 is connected to GND, and the other end is connected to the non-inverting input of U1.2, and the inverting input of U1.2 is connected to Vref-3. Resistor R14 is a positive feedback resistor. One end of R14 is connected to the output of U1.2, and the other end is connected to the non-inverting input of U1.2. R16 is a pull-up resistor to prevent the open drain state when the output is high. One end of R16 is connected to VCC, and the other end is connected to the output of U1.2. U1.2 is a hysteresis comparator that can suppress noise and burrs. R13 and LED1 form an output indication circuit. One end of R13 is connected to VCC, and the other end is connected to the anode of LED1. The cathode of LED1 is connected to the output of U1.2.

[0040] The input detection circuit is mainly composed of a hysteresis comparator. Resistors R1 and R2 form a sampling circuit. One end of R1 is connected to Vin and the other end is connected to the non-inverting input of U1.1. One end of R2 is connected to GND and the other end is connected to the non-inverting input of U1.1. The inverting input of U1.1 is connected to Vref-1. Resistor R3 is a positive feedback resistor. One end of R3 is connected to the output of U1.1 and the other end is connected to the non-inverting input of U1.1. R4 is a pull-up resistor with the same function as R16. One end of R23 is connected to VCC and the other end is connected to the output of U1.1. R23 and LED2 form an input indication circuit. One end of R23 is connected to GND and the other end is connected to the cathode of LED2. The anode of LED2 is connected to the output of U1.1.

[0041] The circuit is powered on, the thyristor is in the off state, the soft start circuit is turned on, and the three-phase AC power is obtained through the soft start circuit to obtain Vin;

[0042] The input detection circuit works to detect the Vin voltage. After about 2 seconds, the soft start circuit is closed. When the input Vin reaches the opening threshold, it is fed back to the thyristor drive circuit. The thyristor drive circuit turns on the thyristor. The three-phase AC power passes through the thyristor module and obtains Vin.

[0043] The main circuit starts to work normally and outputs Vbus;

[0044] The output detection circuit starts working after detecting the Vbus output;

[0045] When Vbus is detected to be abnormal and exceeds the set threshold, a feedback signal is given to the thyristor drive circuit, the thyristor drive circuit will turn off the thyristor and the circuit will stop working.

[0046] Among them, U1.1 is a hysteresis comparator. The threshold voltage requires separate analysis of the output result. When the output is high level, the output terminal is pulled up to high level. At this time, the threshold rising threshold Uth satisfies , and finally the calculated Uth is: , when the output is low level, the output terminal is grounded. At this time, the threshold falling threshold Utl satisfies: , and finally the calculated Utl is: ;

[0047] When the input terminal of U1.1 satisfies that Vref - 1 is greater than Uth, the output of U1.1 flips to low level. When the input terminal of U1.1 satisfies that Vref - 1 is less than Utl, the output of U1.1 flips to high level. When it is high level, LED2 lights up, indicating that Vin meets the turn - on threshold. At this time, there is no input at the inverting input terminal of U2.1, U2.1 outputs high level, the non - inverting input terminal of U1.2 must be greater than the inverting input terminal of U1.2, U1.2 outputs high level, both D1 and D2 are reverse - cut - off, and the main circuit starts to operate;

[0048] During normal operation, the output detection circuit also starts to work. Under normal working conditions, the voltage at the inverting input terminal of U2.1 (i.e., the Vus sampling voltage) is lower than Vref - 2, U2.1 outputs high level, and U1.2 also outputs high level;

[0049] U1.2 is also a hysteresis comparator. The threshold voltage requires separate analysis of the output result. When the output is high level, the output terminal is pulled up to high level. At this time, the threshold rising threshold Uth1 satisfies , and finally the calculated Uth1 is:

[0050] , when the output is low level, the output terminal is grounded. At this time, the threshold falling threshold Utl1 satisfies: , and finally the calculated Utl1 is: ;

[0051] When the input terminal value of U1.2 satisfies that Vref - 3 is greater than Uth1, the output of U1.2 flips to low level. When the input terminal of U1.2 satisfies that Vref - 3 is less than Utl, the output of U1.2 flips to high level.

[0052] Under normal working conditions, D1 and D2 are both non - conducting, Q2 is saturated and conducting, there is no voltage input at the base of Q5, Q5 is non - conducting, the output is high level, through the gate of Q4, Q4 is conducting, the 2 - pin of U3 is connected to GND, then U3 is conducting, Q3 is saturated and conducting, the 1 - pin of relay K1 is connected to GND - 1, the relay is attracted, the thyristor meets the turn - on condition, and the circuit works normally;

[0053] When U1.1 outputs a low level (i.e., the input voltage does not reach the turn-on condition), D2 conducts, Q2 cannot conduct, and the circuit will not be able to start running. At the same time, if during normal operation, U1.2 outputs a low level, D1 will conduct, Q2 still cannot conduct, the circuit will stop running, and at the same time, the LED1 light will turn on to indicate an output fault.

[0054] The examples described in the present utility model only describe the preferred embodiments of the present utility model, and do not limit the concept and scope of the present utility model. Without departing from the design concept of the present utility model, various deformations and improvements made by those skilled in the art to the technical solutions of the present utility model should fall within the protection scope of the present utility model.

Claims

1. A protection circuit based on thyristor, characterized in that: include: Thyristor module, soft start circuit, thyristor drive circuit, input detection circuit and output detection circuit; The thyristor module is electrically connected to the soft start circuit, the thyristor drive circuit, the input detection circuit and the output detection circuit are connected through diodes D1 and D2, and the thyristor module is connected to the thyristor drive circuit through a relay K1.

2. The circuit according to claim 1, characterized in that The thyristor module is a three-phase bridge half-controlled rectifier circuit. The three-phase AC power is connected to the input pins 4, 5 and 6 of the thyristor module respectively. The control electrode pins 1, 2 and 3 of the thyristor module are connected to the relay K1 in the thyristor drive circuit. The output pins of the thyristor module are 7 and 8, among which pin 7 is connected to GND-2.

3. The circuit according to claim 1, characterized in that In the thyristor drive circuit, diodes D1 and D2 are used for clamping, the cathode of diode D1 is connected to the output signal of the output detection circuit, the cathode of D2 is connected to the output signal of the input detection circuit, and the anodes of diodes D1 and D2 are connected to the base of NPN transistor Q2; resistor R5 is a pull-up resistor, one end of which is connected to the power supply VCC and the other end is connected to the base of Q2; R6 is a pull-down resistor, one end of which is connected to GND and the other end is connected to the base of Q2; resistors R7 and R22 are both current limiting resistors, one end of R7 is connected to VCC and the other end is connected to the collector of Q2, one end of R22 is connected to VCC and the other end is connected to the collector of Q5; the emitters of NPN transistors Q5 and Q2 are both connected to GND, the base of Q5 is connected to the collector of Q2, and Q2 and Q5 realize the role of input and output signals in phase; the anode of diode D4 is connected to the collector of Q5, and the cathode is connected to the gate of N-type MOS, namely Q4; one end of capacitor C3 is connected to the collector of Q4 The gate is connected to the other end of the circuit, and the other end is connected to GND. C3 and D4 form a peak detection circuit to detect and maintain the maximum value of the input; resistor R12 is a discharge pull-down resistor, one end of which is connected to the gate of Q4 and the other end is connected to GND; the drain of Q4 is connected to the 2nd pin of the optocoupler U3, and the source is connected to GND; resistor R10 is a current limiting resistor, one end of which is connected to VCC and the other end is connected to the 1st pin of U3; resistor R9 is a current limiting resistor, one end of which is connected to VCC-1 and the other end is connected to the 4th pin of U3; Resistor R24 ​​is the base resistor of Q3, one end of which is connected to pin 3 of U3, and the other end is connected to the base of Q3; R8 is a pull-down resistor, one end of which is connected to the base of Q3, and the other end is connected to GND-1; the emitter of NPN transistor Q3 is connected to GND-1, and the collector is connected to pin 1 of K1; pin 3 of relay K1 is connected to VCC-2, and pin 4 is connected to VCC-1; D5 is the freewheeling diode of the relay coil, the cathode is connected to pin 4 of K1, and the anode is connected to pin 1 of K1.

4. The circuit according to claim 1, characterized in that The input detection circuit includes a hysteresis comparator U1.1; one end of the resistor R1 is connected to Vin, and the other end is connected to the non-inverting input terminal of U1.1, one end of R2 is connected to GND, and the other end is connected to the non-inverting input terminal of U1.1, and the inverting input terminal of U1.1 is connected to Vref-1; the resistor R3 is a positive feedback resistor, one end of R3 is connected to the output terminal of U1.1, and the other end is connected to the non-inverting input terminal of U1.1; R4 is a pull-up resistor, one end of which is connected to VCC, and the other end is connected to the output terminal of U1.1; R23 and LED2 constitute an input indication circuit, one end of R23 is connected to GND, and the other end is connected to the cathode of LED2, and the anode of LED2 is connected to the output terminal of U1.

1.

5. The circuit according to claim 1, characterized in that The output detection circuit includes two comparators U2.1 and U1.2; one end of resistor R20 is connected to Vbus, and the other end is connected to the inverting input of U2.1; one end of R21 is connected to GND, and the other end is connected to the inverting input of U2.1; the non-inverting input of U2.1 is connected to Vref-2; the output of U2.1 is connected to the non-inverting input of U1.2; resistors R17 and R15 act as voltage dividers, one end of R17 is connected to VCC, and the other end is connected to the non-inverting input of U1.2; one end of R15 is connected to GND, and the other end is connected to the non-inverting input of U1.

2. The inverting input of U1.2 is connected to Vref-3; resistor R14 is a positive feedback resistor, one end of R14 is connected to the output of U1.2, and the other end is connected to the non-inverting input of U1.2; R16 is a pull-up resistor to prevent an open drain state when the output is high, one end of which is connected to VCC, and the other end is connected to the output of U1.2; U1.2 is a hysteresis comparator, which can suppress noise and glitches; R13 and LED1 constitute an output indication circuit, one end of R13 is connected to VCC, and the other end is connected to the anode of LED1, and the cathode of LED1 is connected to the output of U1.

2.

6. The circuit according to claim 4, characterized in that The input detection circuit includes: When the output is high, the rising threshold is Uth; when the output is low, the falling threshold is Utl; When the input of U1.1 satisfies that Vref-1 is greater than Uth, the output of U1.1 flips and becomes a low level. When the input of U1.1 satisfies that Vref-1 is less than Utl, the output of U1.1 flips and becomes a high level. When it is a high level, LED2 lights up, indicating that Vin meets the turn-on threshold. At this time, there is no input at the inverting input of U2.1, and U2.1 outputs a high level. The non-inverting input of U1.2 must be greater than the inverting input of U1.2, and U1.2 outputs a high level. D1 and D2 are both reversely cut off, and the main circuit starts to run.

7. The circuit according to claim 5, characterized in that The output detection circuit includes: When the output is high level, the rising threshold is Uth1; when the output is low level, the falling threshold is Utl1; Among them, when the input value of U1.2 satisfies Vref-3 greater than Uth1, the output of U1.2 flips and becomes a low level. When the input value of U1.2 satisfies Vref-3 less than Utl1, the output of U1.2 flips and becomes a high level. Under normal working conditions, D1 and D2 are not conducting, Q2 is saturated and conducting, there is no voltage input to the base of Q5, Q5 is not conducting, the output is high level, through the gate of Q4, Q4 is conducting, pin 2 of U3 is connected to GND, then U3 is turned on, Q3 is saturated and conducting, pin 1 of relay K1 is connected to GND-1, the relay is energized, the thyristor meets the opening conditions, and the circuit works normally.

8. A switching power supply based on thyristor, characterized in that: comprising a main circuit, a control and auxiliary circuit and a protection circuit as claimed in any one of claims 1 to 7; Among them, Vin and GND of the main circuit are connected to the thyristor module in the protection circuit and Vin and GND of the soft start circuit, the output Vbus and Vin of the main circuit are connected to the output detection circuit and the input detection circuit respectively, and the main circuit is connected to the sampling resistor in the output detection circuit in the protection circuit through the control and auxiliary circuit.