Front-end input protection circuit of switching power supply

Abstract

The invention relates to a front-end input protection circuit of a switching power supply, which comprises a rectifying circuit, a power supply circuit and an overvoltage protection circuit, and is characterized in that the input end of the power supply circuit is connected with the output end of the rectifying circuit; the overvoltage protection circuit comprises an overvoltage detection circuit, a control circuit and a single-pole double-throw relay KM, the input end of the overvoltage detection circuit is connected with the output end of the rectification circuit, the output end of the overvoltage detection circuit is connected with the control circuit, and the output end of the power supply circuit is connected with the single-pole double-throw relay KM through the control circuit. The normally closed contact of the single-pole double-throw relay KM is used for cutting off or closing the output of the switching power supply, the overvoltage detection circuit is used for detecting whether the input voltage exceeds a preset value, and when the input voltage exceeds the preset value, the overvoltage detection circuit outputs a current signal to the control circuit, so that the control circuit is switched on, and the power supply circuit supplies power to the single-pole double-throw relay KM; and the single-pole double-throw relay KM is electrified to cut off the output of the switching power supply. According to the invention, overvoltage protection of the front-end input of the switching power supply can be efficiently carried out.

Description

Technical Field

[0001] The present application relates to the field of switching power supplies, and in particular to a front-end input protection circuit of a switching power supply. Background Art

[0002] Overvoltage protection is a function that needs to be considered for any electronic product. The input overvoltage protection of the power supply generally uses a varistor as an overvoltage protection device. However, the overvoltage protection method using a varistor has a single protection. Overvoltage can easily damage electronic components and there is no effective guarantee for the protection of subsequent circuits and components. It is easy for the overvoltage to exceed a certain value, causing the overvoltage voltage to damage the varistor and cause damage to the switching power supply at the same time. Based on this situation, a more thorough solution for overvoltage protection within a certain overvoltage range is needed. Physical protection is the most effective and reliable protection method. By effectively cutting off the loop connection, the safety of the subsequent circuit can be effectively protected during overvoltage.

[0003] However, the existing physical protection methods also have defects and shortcomings: there are overvoltage protection products with special physical protection on the market, but they are almost all single product devices that require fixed external installation methods. If used on the original products that need to be protected, customers objectively need to consider whether the finished product and appearance structure of the protection device and the usage scenario meet the requirements. In summary, there are many limitations caused by the above situation. 1. The external protector is generally equipped with an installation device such as a guide rail device in the usage scenario. This is a defect in the usage scenario with limited space; 2. The independent protector is designed as an independent product, so its cost is high, and the required docking wiring is more cumbersome. Therefore, it needs to be improved. Summary of the invention

[0004] In order to improve the overvoltage protection effect of a switching power supply and reduce costs at the same time, the present application provides a front-end input protection circuit of a switching power supply.

[0005] The present application provides a front-end input protection circuit of a switching power supply, which adopts the following technical solution: a front-end input protection circuit of a switching power supply, comprising: A rectifier circuit, the rectifier circuit is used to rectify the input alternating current into direct current; A power supply circuit, wherein an input end of the power supply circuit is connected to an output end of the rectifier circuit; Overvoltage protection circuit. The overvoltage protection circuit includes an overvoltage detection circuit, a control circuit, and a single-pole double-throw relay KM. The input end of the overvoltage detection circuit is connected to the output end of the rectification circuit. The output end of the overvoltage detection circuit is connected to the control circuit. The output end of the power supply circuit is connected to the single-pole double-throw relay KM through the control circuit. The normally closed contact of the single-pole double-throw relay KM is used to cut off or close the output of the switching power supply. The overvoltage detection circuit is used to detect whether the input voltage exceeds a preset value. When it exceeds the preset value, the overvoltage detection circuit outputs a current signal to the control circuit, so that the control circuit is turned on. The power supply circuit supplies power to the single-pole double-throw relay KM, and the single-pole double-throw relay KM is powered on to cut off the output of the switching power supply.

[0006] By adopting the above technical solution, the accessed alternating current is rectified and output as direct current through the rectification circuit. The power supply circuit provides a low voltage to the control circuit. When the overvoltage detection circuit detects that the accessed voltage exceeds the preset value, it outputs a current signal to the control circuit, so that the control circuit is turned on. The power supply circuit supplies power to the single-pole double-throw relay KM, so that the normally closed contact switch of the single-pole double-throw relay KM is opened, thereby cutting off the power output. When the voltage returns to the normal range, the single-pole double-throw relay KM returns to the normally closed contact, which can effectively prevent the damage of the electronic components at the rear stage of the switching power supply due to the sudden change of the input voltage during use. And compared with the prior art, it is embedded inside the original switching power supply, so that the volume is small, additional independent components can be saved, and the cost can be reduced.

[0007] Preferably, the power supply circuit includes a power management chip U1, an inductor L1, a filter circuit, and a voltage stabilizing circuit. The power management chip U1 is connected to the rectification circuit and the inductor L1. The input end of the filter circuit is connected to one end of the inductor L1. The output end of the filter circuit is connected to the input end of the voltage stabilizing circuit. The output end of the voltage stabilizing circuit is connected to the control circuit.

[0008] By adopting the above technical solution, the high-voltage direct current output by the rectification circuit is converted into low-voltage direct current by the power management chip U1, the inductor L1, and the filter circuit and given to the control circuit and the single-pole double-throw relay KM, so as to provide a stable power supply for the single-pole double-throw relay KM, and thus there is no need to externally configure a power supply.

[0009] Preferably, the overvoltage detection circuit includes a plurality of series-connected voltage-dividing resistors and a voltage-regulating diode SHR3. The plurality of series-connected voltage-dividing resistors are connected to the output end of the rectifying circuit. The reference terminal of the voltage-regulating diode SHR3 is connected between the plurality of voltage-dividing resistors. The anode of the voltage-regulating diode SHR3 is grounded. The voltage-regulating diode SHR3 is connected to the control circuit through a load resistor. The output end of the voltage-regulating circuit is connected to one end of a single-pole double-throw relay KM through the control circuit, and the other end of the single-pole double-throw relay KM is grounded.

[0010] By adopting the above technical solution, the voltage output by the rectifying circuit is divided by a plurality of series-connected voltage-dividing resistors and then connected to the reference terminal of the voltage-regulating diode SHR3. When the voltage input to the switching power supply increases and exceeds the voltage at the reference terminal of the voltage-regulating diode SHR3, the voltage-regulating diode SHR3 conducts, thereby enabling the control circuit to conduct, and further causing the normally-closed contact switch of the single-pole double-throw relay KM to disconnect, so that the switching power supply is cut off for overvoltage protection.

[0011] Preferably, it further includes an electrolytic capacitor EC1. The positive electrode of the electrolytic capacitor EC1 is connected to the output end of the rectifying circuit, and the negative electrode of the electrolytic capacitor EC1 is grounded.

[0012] By adopting the above technical solution, the electrolytic capacitor EC1 connected to the output end of the rectifying circuit functions to stabilize voltage, filter, and store electrical energy.

[0013] Preferably, it further includes a power release circuit. The power release circuit is connected in parallel with the electrolytic capacitor EC1 and is used to quickly release the remaining power of the electrolytic capacitor EC1 before the normally-closed contact switch of the single-pole double-throw relay KM closes. The power release circuit includes a triode Q11, a diode D4, a load resistor R41, and a load resistor R42. The emitter of the triode Q11 is connected to the positive electrode of the electrolytic capacitor EC1. The collector of the triode Q11 is connected to one end of the load resistor R41. The other end of the load circuit R41 is grounded. The positive electrode of the diode D4 is connected to the base of the triode Q11. The negative electrode of the diode D4 is electrically connected to the emitter of the triode Q11. One end of the load resistor R42 is connected to the base of the triode Q11, and the other end of the load resistor R42 is grounded.

[0014] By adopting the above technical solution, when the normally-closed contact switch of the single-pole double-throw relay KM is cut off, there is remaining power in the electrolytic capacitor EC1. Therefore, before the normally-closed contact switch closes, it is necessary to quickly release the power in the electrolytic capacitor EC1 to avoid damage to the subsequent circuit. Through the current amplification effect of the triode Q11 and the blocking effect of the diode D4, the power in the electrolytic capacitor EC1 is quickly released.

[0015] Preferably, an electrolytic capacitor EC2 is connected in series with the electrolytic capacitor EC1, and the electrolytic capacitor EC2 is connected in parallel with the normally closed contact switch of the single-pole double-throw relay KM.

[0016] By adopting the above technical solution, in the case of no overvoltage protection, the normally closed contact switch of the single-pole double-throw relay is closed, the electrolytic capacitor EC2 is short-circuited, and the input electric energy is stored in EC1. At this time, the capacitance value of EC1 remains its original value; when the input voltage is overvoltage, the normally closed contact of the single-pole double-throw relay KM is disconnected. At this time, the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are connected in series, so that the voltage will not be transmitted to the subsequent stage. Also, because the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are connected in series, the overvoltage withstand value increases, thus playing a role in protecting the electrolytic capacitor EC1; according to the above control method, when the input voltage is overvoltage, it can be automatically switched so that the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are connected in series to increase the voltage withstand range. When there is no overvoltage, only the electrolytic capacitor EC1 is used, and the electrolytic capacitor EC2 does not participate in the series connection. Thus, the capacitance value of the electrolytic capacitor EC1 will not be reduced due to the series connection method, and it can store enough energy to supply the subsequent circuit under normal working conditions. Thus, it can achieve that multiple capacitors are connected in series to increase the voltage withstand while avoiding the problem that the capacitance value is reduced due to the series connection of capacitors, resulting in insufficient power.

[0017] Preferably, a diode D5 is connected in series with the electrolytic capacitor EC2. The positive pole of the diode D5 is connected to the negative pole of the electrolytic capacitor EC2, and the negative pole of the diode D5 is connected to the positive pole of the electrolytic capacitor EC1.

[0018] By adopting the above technical solution, the diode D5 can raise the potential energy of the electrolytic capacitor EC2 being boosted and transfer it to you all, and accelerate the self-discharge speed of the electrolytic capacitor EC2 when the single-pole double-throw relay KM restores its normally closed contact.

[0019] Preferably, an inductor L2 is connected in series with the normally closed contact switch of the single-pole double-throw relay KM.

[0020] By adopting the above technical solution, when the normally closed contact of the single-pole double-throw relay attracts and the electrolytic capacitor EC2 discharges, the inductor L2 is used to suppress the instantaneous surge peak by applying Lenz's law of the inductor.

[0021] Preferably, a capacitor C5 is connected in parallel with the normally closed contact switch of the single-pole double-throw relay KM.

[0022] By adopting the above technical solution, the capacitor C5 is used as an absorption capacitor and is also used to absorb the instantaneous peak.

[0023] In summary, the present application includes at least one of the following beneficial technical effects: 1. The rectifier circuit rectifies the incoming alternating current and outputs direct current. The power supply circuit provides low voltage to the control circuit. When the overvoltage detection circuit detects that the incoming voltage exceeds the preset value, it outputs a current signal to the control circuit, causing the control circuit to conduct. The power supply circuit powers the single-pole double-throw relay KM, causing the normally closed contact switch of the single-pole double-throw relay KM to open, thus cutting off the power output. When the voltage returns to the normal range, the single-pole double-throw relay KM returns to its normally closed contact, effectively preventing damage to the electronic components at the rear stage of the switching power supply due to sudden changes in the input voltage during use. Compared with the prior art, it is embedded inside the original switching power supply, making it small in size, capable of saving additional independent components, and thus reducing costs. 2. In the case of no overvoltage protection, the normally closed contact switch of the single-pole double-throw relay KM is closed, and the electrolytic capacitor EC2 is short-circuited. The input electrical energy is stored in EC1, and at this time, the capacitance value of EC1 remains its original value. When the input voltage is overvoltage, the normally closed contact of the single-pole double-throw relay KM opens. At this time, the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are in series, so that the voltage will not be transmitted to the rear stage. Also, because the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are in series, the overvoltage withstand value increases, thus playing a role in protecting the electrolytic capacitor EC1. According to the above control method, when the input voltage is overvoltage, it can be automatically switched so that the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are in series to increase the voltage withstand range. When there is no overvoltage, only the electrolytic capacitor EC1 is used, and the electrolytic capacitor EC2 does not participate in the series connection, so that the capacitance value of the electrolytic capacitor EC1 is not reduced due to the series connection method, and it can store enough energy to supply the rear-stage circuit under normal working conditions, thus realizing that multiple capacitors in series increase the voltage withstand while avoiding the problem of reduced capacitance value caused by capacitor series connection and insufficient power. Description of the Drawings

[0024] Figure 1 It is the circuit schematic diagram of the rectifier circuit, power supply circuit and overvoltage protection circuit in the embodiment of the present application.

[0025] Figure 2 It is the circuit schematic diagram of the switching power supply with a power release circuit in the embodiment of the present application.

[0026] Figure 3 It is the circuit schematic diagram of the switching power supply in the embodiment of the present application.

[0027] Description of the reference numerals: 1. Rectifier circuit; 2. Power supply circuit; 21. Filter circuit; 22. Voltage stabilizing circuit; 3. Overvoltage protection circuit; 31. Overvoltage detection circuit; 32. Control circuit; 4. Power release circuit. Detailed Embodiments

[0028] The following will further elaborate on the present application in conjunction with the attached Figures 1-3 drawings.

[0029] The embodiments of the present application disclose a front-end input protection circuit for a switching power supply. Refer to Figure 1 , the front-end input protection circuit includes a rectification circuit 1, a power supply circuit 2, and an overvoltage protection circuit 3. The rectification circuit 1 in the present application is a bridge rectification circuit, which is used to rectify the input alternating current into direct current. The input end of the power supply circuit 2 is connected to the output end of the rectification circuit 1, and is used to convert the high-voltage direct current output by the rectification circuit 1 into low-voltage direct current. The overvoltage protection circuit 3 is used to detect whether the input voltage exceeds a preset value, so as to control the cut-off of the output of the switching power supply.

[0030] Specifically, the overvoltage protection circuit 3 includes an overvoltage detection circuit 31, a control circuit 32, and a single-pole double-throw relay KM. The input end of the overvoltage detection circuit 31 is connected to the output end of the rectification circuit 1, the output end of the overvoltage detection circuit 31 is connected to the control circuit 32, and the output end of the power supply circuit 2 is connected to the single-pole double-throw relay KM through the control circuit 32 for supplying power to the single-pole double-throw relay KM. The normally closed contact of the single-pole double-throw relay KM is used to cut off or close the front-end output of the switching power supply. The overvoltage detection circuit 31 is used to detect whether the input voltage exceeds the preset value. When it exceeds the preset value, the overvoltage detection circuit 31 outputs a signal to the control circuit 32, so that the control circuit 32 is turned on, the power supply circuit 2 supplies power to the single-pole double-throw relay KM, the single-pole double-throw relay KM is energized, and the output of the switching power supply is cut off.

[0031] The overvoltage detection circuit 31 includes a plurality of series-connected voltage-dividing resistors and a voltage-regulating diode SHR3. The plurality of series-connected voltage-dividing resistors are connected to the output end of the rectification circuit 1. The reference terminal of the voltage-regulating diode SHR3 is connected between the plurality of voltage-dividing resistors. The anode of the voltage-regulating diode SHR3 is grounded, and the voltage-regulating diode SHR3 is connected to the control circuit 32 through a load resistor R26. Specifically, the plurality of voltage-dividing resistors in the present application include a voltage-dividing resistor R20, a voltage-dividing resistor R21, and a voltage-dividing resistor R22. The reference terminal of the voltage-regulating diode SHR3 is connected between the voltage-dividing resistor R21 and the voltage-dividing resistor R22. The voltage-regulating diode SHR3 in the present application uses TL431.

[0032] The control circuit 32 includes a triode Q1 and a pull-down resistor R27. The base of the triode Q1 is electrically connected to the load resistor R26. One end of the pull-down resistor R27 is connected to the base of the triode Q1, and the other end is connected to the emitter of the triode Q1. The emitter of the triode Q1 is connected to the power supply circuit 2.

[0033] The voltage output by the rectification circuit 1 is divided by multiple series-connected voltage-dividing resistors and then connected to the reference terminal of the voltage-regulating diode. When the input voltage exceeds the voltage at the reference terminal of the voltage-regulating diode SHR3, the voltage-regulating diode SHR3 conducts, thereby enabling the control circuit 32 to conduct, and further causing the normally-closed contact switch of the single-pole double-throw relay KM to open, thus cutting off the switching power supply for overvoltage protection. When the input voltage returns to the normal voltage range, the voltage-regulating diode SHR3 does not conduct, thereby de-energizing the single-pole double-throw relay KM, and thus the normally-closed contact switch of the single-pole double-throw relay KM closes, enabling the front end of the switching power supply to output normally.

[0034] Specifically, the power supply circuit 2 includes a power management chip U1, an inductor L1, a filtering circuit 21, and a voltage-regulating circuit 22. The power management chip U1 in this application uses the model OB2223AP. The 1st pin, 5th pin, and 6th pin of the power management chip U1 are connected to the output terminal of the rectification circuit 1. The 4th pin of the power management chip U1 is connected to one end of the inductor L1. The other end of the inductor L1 is connected to the filtering circuit 21. The other end of the filtering circuit 21 is connected to the voltage-regulating circuit 22. The output terminal of the voltage-regulating circuit 22 is connected to the control circuit 32. The control circuit 32 and the single-pole double-throw relay KM are powered by the power management chip U1, the inductor L1, and the filtering circuit 21, thereby providing a stable power supply for the single-pole double-throw relay KM, and thus eliminating the need for an external power supply.

[0035] The voltage-regulating circuit 22 includes a triode Q18, a pull-down resistor R40, and a voltage-regulating diode ZD5. The collector of the triode Q18 is connected to the output terminal of the filtering circuit 21. The emitter of the triode Q18 is connected to the emitter of the triode Q1. The base of the triode Q18 is connected to the negative electrode of the voltage-regulating diode ZD5. The positive electrode of the voltage-regulating diode ZD5 is grounded. One end of the pull-down resistor R40 is connected to the collector of the triode Q18, and the other end is connected to the base of the triode Q18.

[0036] Refer to Figure 2 Existing switching power supplies also include an electrolytic capacitor EC1. The positive electrode of the electrolytic capacitor EC1 is connected to the output terminal of the rectification circuit 1, and the negative electrode of the electrolytic capacitor EC1 is grounded. The electrolytic capacitor EC1 connected to the output terminal of the rectification circuit 1 functions to stabilize voltage, filter, and store electrical energy. Therefore, it is necessary to consider the withstand voltage value and capacitance value of the electrolytic capacitor EC1. The higher the withstand voltage value of the electrolytic capacitor EC1, the more it can avoid damage to the electrolytic capacitor EC1 during overvoltage, and the capacitance value of the electrolytic capacitor EC1 can increase the output power of the switching power supply.

[0037] It also includes a power release circuit 4. The power release circuit 4 is connected in parallel with the electrolytic capacitor EC1 and is used to quickly release the remaining power of the electrolytic capacitor EC1 before the normally closed contact switch of the single-pole double-throw relay KM is closed. The power release circuit 4 includes a triode Q11, a diode D4, a load resistor R41, and a load resistor R42. The emitter of the triode Q11 is connected to the positive pole of the electrolytic capacitor EC1. The collector of the triode Q11 is connected to one end of the load resistor R41. The other end of the load circuit R41 is grounded. The positive pole of the diode D4 is connected to the base of the triode Q11. The negative pole of the diode D4 is connected to the emitter of the triode Q11. One end of the load resistor R42 is connected to the base of the triode Q11, and the other end of the load resistor R42 is grounded. When the normally closed contact switch of the single-pole double-throw relay KM is cut off, there is remaining power in the electrolytic capacitor EC1. Therefore, before the normally closed contact switch is closed, it is necessary to quickly release the power in the electrolytic capacitor EC1 directly to avoid damaging the subsequent circuit. Through the current amplification effect of the triode Q11 and the blocking effect of the diode D4, the power in the electrolytic capacitor EC1 is quickly released directly.

[0038] When the switching power supply is in an overvoltage state, the output at the back end is cut off. Therefore, the larger the withstand voltage value range of the electrolytic capacitor EC1, the less likely it is to be damaged by voltage breakdown. And the higher the capacitance value of the electrolytic capacitor, the higher the output power of the switching power supply can be improved.

[0039] Refer to Figure 3 , an electrolytic capacitor EC2 is connected in series with the electrolytic capacitor EC1, and the electrolytic capacitor EC2 is connected in parallel with the normally closed contact switch of the single-pole double-throw relay KM. In the case of no overvoltage protection, the normally closed contact switch of the single-pole double-throw relay is closed, and the electrolytic capacitor EC2 is short-circuited. The input electrical energy is stored in EC1. At this time, the capacitance value of EC1 remains its original value. When the input is overvoltage, the normally closed contact of the single-pole double-throw relay KM is disconnected. At this time, the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are connected in series, so that the voltage will not be transmitted to the subsequent stage. And because the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are connected in series, the overvoltage withstand value increases, thus playing a role in protecting the electrolytic capacitor EC1. According to the above control method, when the input is overvoltage, it can be automatically switched so that the electrolytic capacitor EC1 and the electrolytic capacitor EC2 are connected in series to increase the withstand voltage range. When there is no overvoltage, only the electrolytic capacitor EC1 is used, and the electrolytic capacitor EC2 does not participate in the series connection. Thus, the capacitance value of the electrolytic capacitor EC1 will not be reduced due to the series connection method, and it can store enough energy to supply the subsequent circuit under normal working conditions. Thus, multiple capacitors connected in series can increase the withstand voltage while avoiding the problem that the capacitance value is reduced due to the series connection of capacitors, resulting in insufficient power.

[0040] The electrolytic capacitor EC2 is connected in series with a diode D5. The positive electrode of the diode D5 is connected to the negative electrode of the electrolytic capacitor EC2, and the negative electrode of the diode D5 is connected to the positive electrode of the electrolytic capacitor EC1. The diode D5 can raise the potential energy of the electrolytic capacitor EC2 for bootstrap and transfer it to you, and accelerate the self-discharge speed of the electrolytic capacitor EC2 when the single-pole double-throw relay KM restores its normally closed contact. The normally closed contact switch of the single-pole double-throw relay KM is connected in series with an inductor L2. The inductor L2 is used to suppress the instantaneous surge spike by applying Lenz's law of induction when the normally closed contact of the single-pole double-throw relay attracts the electrolytic capacitor EC2 to discharge. The normally closed contact switch of the single-pole double-throw relay KM is connected in parallel with a capacitor C5. The capacitor C5 is used as a snubber capacitor to absorb the instantaneous spike as well.

[0041] The implementation principle of the front-end input protection circuit of a switching power supply in an embodiment of this application is as follows: The incoming alternating current is rectified into direct current by the rectification circuit 1. When the overvoltage detection circuit 31 detects that the incoming voltage exceeds the preset value, it outputs a current signal to the control circuit 32, thereby making the control circuit 32 conduct, and powers the single-pole double-throw relay KM through the multiplexing power supply circuit 2, thereby disconnecting the normally closed contact switch of the single-pole double-throw relay KM, thereby cutting off the front-end output of the switching power supply, thus effectively protecting the subsequent circuit. When the voltage returns to the normal range, the single-pole double-throw relay KM returns to its normally closed contact, thereby effectively preventing damage to the subsequent circuit of the switching power supply due to sudden changes in the input voltage during use. And compared with the prior art, it is embedded inside the original switching power supply, so that the volume is small, additional independent components can be saved, and the cost can be reduced.

[0042] Unless otherwise defined, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those with ordinary skills in the field to which this application belongs. The words "first", "second", "third" and similar words used in the specification and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "a" or "one" do not indicate a quantity limitation either, but indicate that there is at least one. Words such as "including" or "comprising" mean that the elements or objects appearing before "including" or "comprising" cover the elements or objects listed after "including" or "comprising" and their equivalents, and do not exclude other elements or objects. "Up", "down", "left", "right", etc. are only used to represent relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0043] The above are all the preferred embodiments of this application. Without limiting the protection scope of this application accordingly, therefore: All equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A front-end input protection circuit of a switching power supply, characterized in that: include: A rectifier circuit (1), the rectifier circuit (1) is used to rectify input alternating current into direct current; A power supply circuit (2), wherein an input end of the power supply circuit (2) is connected to an output end of the rectifier circuit (1); An overvoltage protection circuit (3), the overvoltage protection circuit (3) comprising an overvoltage detection circuit (31), a control circuit (32), and a single-pole double-throw relay KM, the input end of the overvoltage detection circuit (31) being connected to the output end of the rectifier circuit (1), the output end of the overvoltage detection circuit (31) being connected to the control circuit (32), the output end of the power supply circuit (2) being connected to the single-pole double-throw relay KM via the control circuit (32), the normally closed contact of the single-pole double-throw relay KM being used to cut off or close the output of a switching power supply, the overvoltage detection circuit (31) being used to detect whether the input voltage exceeds a preset value, when the preset value is exceeded, the overvoltage detection circuit (31) outputs a current signal to the control circuit (32), thereby turning on the control circuit (32), the power supply circuit (2) supplies power to the single-pole double-throw relay KM, the single-pole double-throw relay KM is energized, and the output of the switching power supply is cut off.

2. The front-end input protection circuit of the switching power supply according to claim 1, characterized in that: The power supply circuit (2) comprises a power management chip U1, an inductor L1, a filter circuit (21) and a voltage stabilizing circuit (22); the power management chip U1 is connected to the rectifier circuit (1) and the inductor L1; the input end of the filter circuit (21) is connected to one end of the inductor L1; the output end of the filter circuit (21) is connected to the input end of the voltage stabilizing circuit (22); and the output end of the voltage stabilizing circuit (22) is connected to the control circuit (32).

3. The front-end input protection circuit of the switching power supply according to claim 2, characterized in that: The overvoltage detection circuit (31) comprises a plurality of voltage-dividing resistors connected in series and a voltage-stabilizing tube SHR3, wherein the plurality of voltage-dividing resistors connected in series are connected to the output end of the rectifier circuit (1), the reference end of the voltage-stabilizing tube SHR3 is connected between the plurality of voltage-dividing resistors, the anode of the voltage-stabilizing tube SHR3 is grounded, the voltage-stabilizing tube SHR3 is connected to the control circuit (32) via a load resistor, the output end of the voltage-stabilizing circuit (22) is connected to one end of the single-pole double-throw relay KM via the control circuit (32), and the other end of the single-pole double-throw relay KM is grounded.

4. The front-end input protection circuit of the switching power supply according to claim 1, characterized in that: It also includes an electrolytic capacitor EC1, the positive electrode of the electrolytic capacitor EC1 is connected to the output end of the rectifier circuit (1), and the negative electrode of the electrolytic capacitor EC1 is grounded.

5. The front-end input protection circuit of the switching power supply according to claim 4, characterized in that: The invention also comprises a power release circuit (4), wherein the power release circuit (4) is connected in parallel with the electrolytic capacitor EC1, and the power release circuit (4) is used to quickly release the residual power of the electrolytic capacitor EC1 before the normally closed contact switch of the single-pole double-throw relay KM is closed; the power release circuit (4) comprises a transistor Q11, a diode D4, a load resistor R41, and a load resistor R42, wherein the emitter of the transistor Q11 is connected to the positive electrode of the electrolytic capacitor EC1, the collector of the transistor Q11 is connected to one end of the load resistor R41, the other end of the load circuit R41 is grounded, the positive electrode of the diode D4 is connected to the base of the transistor Q11, the negative electrode of the diode D4 is electrically connected to the emitter of the transistor Q11, one end of the load resistor R42 is connected to the base of the transistor Q11, and the other end of the load resistor R42 is grounded.

6. The front-end input protection circuit of the switching power supply according to claim 4, characterized in that: The electrolytic capacitor EC1 is connected in series with the electrolytic capacitor EC2, and the electrolytic capacitor EC2 is connected in parallel with the normally closed contact switch of the single-pole double-throw relay KM.

7. The front-end input protection circuit of the switching power supply according to claim 6, characterized in that: The electrolytic capacitor EC2 is connected in series with a diode D5 , wherein the anode of the diode D5 is connected to the cathode of the electrolytic capacitor EC2 , and the cathode of the diode D5 is connected to the anode of the electrolytic capacitor EC1 .

8. The front-end input protection circuit of the switching power supply according to claim 1, characterized in that: The normally closed contact switch of the single-pole double-throw relay KM is connected in series with an inductor L2.

9. The front-end input protection circuit of the switching power supply according to claim 1, characterized in that: The normally closed contact switch of the single-pole double-throw relay KM is connected in parallel with a capacitor C5.

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