Switching power supply for taking electricity from direct-current bus of active power filter

Abstract

The invention discloses a switching power supply for taking electricity from a direct-current bus of an active power filter. The switching power supply comprises a power supply chip, a high-voltage power-on starting circuit, a driving circuit, a multi-way switching circuit, a first transformer and a rectifying and filtering circuit, the driving circuit comprises a push-pull circuit and a second transformer, an input end of the push-pull circuit is electrically connected with a control signal output pin of the power supply chip, an output end of the push-pull circuit is electrically connected with a primary winding of the second transformer, and a plurality of secondary windings of the second transformer are electrically connected with control ends of the switching circuits respectively; each switching circuit is electrically connected with an electricity taking contact of the direct-current bus and each primary winding of the first transformer, and is used for controlling the on-off of a circuit between each section of sub direct-current bus divided by the electricity taking contact and each primary winding of the first transformer according to a driving signal output by the driving circuit; a first secondary winding of the first transformer is electrically connected with the input end of the rectification filter circuit, and the output end of the rectification filter circuit serves as the overall output of the power supply.

Description

Technical Field

[0001] This invention relates to the field of power supply technology, and more specifically to a switching power supply that draws power from the DC bus of an active power filter. Background Technology

[0002] Currently, the market uses two methods: AC-side power supply and DC-side full bus power supply with cascaded topology.

[0003] Direct AC power supply, with its active power filter compensating for high-order harmonics, can interfere with the AC-side switching power supply, potentially damaging EMC components. Ensuring normal operation of the AC-side switching power supply under high-order harmonic conditions requires EMC protection adjustments, increasing costs. Furthermore, the DC-side bus capacitors cannot be discharged after grid-side power failure; their self-discharge is lengthy, necessitating waiting for complete discharge before field disassembly. Cascaded topologies with full DC-side bus power supply present significant challenges in consistency control due to their multi-stage series topology. The multi-stage series connection of high-voltage electrolytic capacitors also poses a high risk of voltage imbalance, compromising power supply reliability. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects existing in the prior art and provide a switching power supply with DC bus power extraction that can effectively avoid problems such as the difficulty of consistent control of direct cascaded drive of the entire bus, the high risk of voltage imbalance of multi-stage series capacitors of high-voltage electrolytic capacitors, and the influence of high-order harmonics of AC power supply, and greatly enhance the reliability of the power supply.

[0005] To achieve the above objectives, the technical solution of the present invention is to design a switching power supply with active power filter DC bus power supply, including: power chip, high voltage power-on start-up circuit, drive circuit, multi-channel switching circuit, first transformer and rectifier filter circuit; The input terminal of the high-voltage power-on start-up circuit is electrically connected to the DC bus of the active power filter, and the output terminal of the high-voltage power-on start-up circuit outputs internal power to power the power chip and the drive circuit. The drive circuit includes a push-pull circuit and a second transformer. The input terminal of the push-pull circuit is electrically connected to the control signal output pin of the power chip, and the output terminal of the push-pull circuit is electrically connected to the primary winding of the second transformer. The multiple secondary windings of the second transformer are respectively electrically connected to the control terminal of each switching circuit. Each switching circuit is electrically connected to the power take-up contacts of the DC bus and each primary winding of the first transformer, respectively, and is used to control the circuit connection and disconnection between each segment of the DC bus divided by the power take-up contacts and each primary winding of the first transformer according to the drive signal output by the drive circuit. The primary winding of the first transformer is electrically connected to the input terminal of the rectifier and filter circuit, and the output terminal of the rectifier and filter circuit serves as the output of the entire power supply.

[0006] Furthermore, among the power-taking contacts at both ends of each DC bus segment, the potential of the first power-taking contact is higher than the potential of the second power-taking contact. The multi-channel switching circuit includes a first switching circuit, which controls the circuit connection and disconnection between the first sub-DC bus and the first primary winding of the first transformer. The first switching circuit includes a first capacitor, a first resistor, a first diode, a first MOSFET, a second diode, and a second resistor. The first terminal of the first capacitor, the first terminal of the first resistor, and the first terminal of the first primary winding of the first transformer are electrically connected to the first power-taking contact of the first sub-DC bus. The second terminal of the first capacitor and the second terminal of the first resistor are connected in parallel to the cathode of the first diode. The anode of the first diode and the first terminal of the first MOSFET are connected in parallel to the second terminal of the first primary winding of the first transformer. The gate of the first MOSFET is electrically connected to the first primary winding of the second transformer. The second terminal of the first MOSFET is electrically connected to the second power-taking contact of the first sub-DC bus.

[0007] Furthermore, the rectifier filter circuit includes a bidirectional rectifier diode, a second capacitor, a third capacitor, and a fourth capacitor; The anode of the bidirectional rectifier diode is electrically connected to the first end of the primary winding of the first transformer. The cathode of the bidirectional rectifier diode serves as the positive output terminal of the power supply system. The positive terminals of the second capacitor, the third capacitor, and the fourth capacitor are connected in parallel to the cathode of the bidirectional rectifier diode. The second end of the primary winding of the first transformer, the negative terminal of the second capacitor, the negative terminal of the third capacitor, and the second end of the fourth capacitor are connected in parallel to ground.

[0008] Furthermore, the high-voltage power-on start-up circuit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a second MOSFET, a third MOSFET, a Zener diode, a third diode, a fifth capacitor, and a sixth capacitor; The third, fourth, fifth, sixth, and seventh resistors are connected in series with the cathode of the third diode. The anode of the third diode is grounded. One end of the third resistor and the first terminal of the second MOSFET are connected in parallel to the positive terminal contact of the DC bus. The second terminal of the second MOSFET is electrically connected to the first terminal of the third MOSFET. The gate of the second MOSFET is connected in parallel between the fifth and sixth resistors. The cathode of the Zener diode is connected in parallel to the gate of the second MOSFET. The anode of the Zener diode is connected in parallel to the second terminal of the second MOSFET. The gate of the third MOSFET is connected in parallel between the seventh resistor and the third diode. The second terminal of the third MOSFET, the first terminal of the fifth capacitor, and the first terminal of the sixth capacitor are connected in parallel to the output terminal of the high-voltage power-on start-up circuit. The second terminals of the fifth and sixth capacitors are grounded.

[0009] Furthermore, the switching power supply also includes a winding power supply circuit, which includes a seventh capacitor, a fourth diode, a first transistor, a fifth diode, an eighth resistor, an eighth capacitor, a ninth capacitor, a sixth diode, and the second stage winding of the first transformer. The first terminal of the seventh capacitor and the cathode of the fourth diode are connected in parallel to the output terminal of the high-voltage power-on starting circuit. The anode of the fourth diode is electrically connected to the first terminal of the first transistor. The second terminal of the first transistor is electrically connected to the first terminal of the eighth capacitor and the cathode of the fifth diode. The base of the first transistor is electrically connected to the cathode of the sixth diode. The anode of the fifth diode is electrically connected to the first terminal of the second winding of the first transformer. The second terminal of the second winding of the first transformer, the second terminal of the eighth capacitor, the anode of the sixth diode, and the second terminal of the seventh capacitor are grounded. The eighth resistor is connected in parallel between the second terminal and the base of the first transistor. The ninth capacitor is connected in parallel across the six diodes. The winding power supply circuit is used to output the internal power supply to power the power chip and the drive circuit after the high-voltage power-on start circuit is powered on, and to cut off the output of the high-voltage power-on start circuit.

[0010] Furthermore, the switching power supply also includes a feedback circuit, which includes a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a tenth capacitor, a first reference voltage source, a first optocoupler, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, and a second transistor. The first end of the ninth resistor and the first end of the tenth resistor are connected in parallel to the output terminal of the rectifier filter circuit. The second end of the ninth resistor is electrically connected to the anode of the first optocoupler. The second end of the tenth resistor is electrically connected to the first end of the eleventh resistor. The reference electrode of the first reference voltage source is connected in parallel between the tenth and eleventh resistors. The cathode of the first reference voltage source is electrically connected to the cathode of the first optocoupler. The anode of the first reference voltage source and the second end of the eleventh resistor are grounded. The tenth capacitor is connected in parallel between the anode and the reference electrode of the first reference voltage source. The twelfth resistor is connected in parallel between the anode and the cathode of the first optocoupler. The collector of the first optocoupler is connected in parallel to the first end of the thirteenth resistor and the first end of the fourteenth resistor. The emitter of the first optocoupler is grounded. The second end of the thirteenth resistor is electrically connected to the reference voltage pin of the power chip. The second end of the fourteenth resistor is electrically connected to the base of the second transistor. The emitter of the second transistor is electrically connected to the compensation pin of the power chip. The collector of the second transistor is grounded. The fifteenth resistor is connected in parallel between the base and the emitter of the second transistor. The second transistor is a PNP transistor.

[0011] Furthermore, the switching power supply also includes an overvoltage protection circuit and a third transistor. The overvoltage protection circuit includes a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a second reference voltage source, a second optocoupler, a twentieth resistor, a twenty-first resistor, and a fourth MOSFET. The first terminals of the sixteenth resistor and the seventeenth resistor are connected in parallel to the output terminal of the rectifier filter circuit. The second terminal of the sixteenth resistor is electrically connected to the anode of the second optocoupler. The second terminal of the seventeenth resistor is electrically connected to the first terminal of the eighteenth resistor. The reference electrode of the second reference voltage source is connected in parallel between the seventeenth and eighteenth resistors. The cathode of the second reference voltage source is electrically connected to the cathode of the second optocoupler. The anode of the second reference voltage source and the second terminal of the eighteenth resistor are grounded. The nineteenth resistor is connected in parallel between the anode and cathode of the second optocoupler. The collector is electrically connected to the first end of the twentieth resistor, the second end of the twentieth resistor is electrically connected to the reference voltage pin of the power supply chip, the emitter of the second optocoupler is electrically connected to the gate of the fourth MOSFET, the source of the fourth MOSFET is grounded, the twentieth eleventh resistor is connected in parallel between the gate and source of the fourth MOSFET, the drain of the fourth MOSFET is electrically connected to the base of the third transistor, the emitter of the third transistor is electrically connected to the compensation pin of the power supply chip, the collector of the third transistor is grounded, and the base of the third transistor is connected in parallel to the reference voltage pin of the power supply chip. The third transistor is a PNP transistor, and the fourth MOSFET is an NMOS transistor.

[0012] Furthermore, the switching power supply also includes a short-circuit protection circuit, which includes a 22nd resistor, a 23rd resistor, a 24th resistor, a 25th resistor, a third reference voltage source, a third optocoupler, a 26th resistor, a 27th resistor, a 28th resistor, a 29th resistor, a 30th resistor, a 31st resistor, a 32nd resistor, an 11th capacitor, a 12th capacitor, a 7th diode, an 8th diode, and an operational amplifier. The first end of the 22nd resistor and the first end of the 23rd resistor are connected in parallel to the output terminal of the rectifier filter circuit. The second end of the 22nd resistor is electrically connected to the anode of the third optocoupler. The second end of the 23rd resistor is electrically connected to the first end of the 24th resistor. The reference electrode of the third reference voltage source is connected in parallel between the 23rd resistor and the 24th resistor. The cathode of the third reference voltage source is electrically connected to the cathode of the third optocoupler. The anode of the third reference voltage source and the second end of the 24th resistor are grounded. The 25th resistor is connected in parallel between the anode and the cathode of the third optocoupler. The collector of the third optocoupler is electrically connected to the first terminal of the 26th resistor, the emitter of the third optocoupler is grounded, the second terminal of the 26th resistor is electrically connected to the first terminal of the 29th resistor, the first terminal of the 11th capacitor is connected in parallel between the 26th and 29th resistors, the second terminal of the 11th capacitor is grounded, the second terminal of the 29th resistor is electrically connected to the inverting input terminal of the operational amplifier, the cathode of the 7th diode and the first terminal of the 27th resistor are connected in parallel between the 26th and 29th resistors, the anode of the 7th diode and the second terminal of the 27th resistor are connected in parallel to the first terminal of the 28th resistor, and the second terminal of the 28th resistor is... The reference voltage is applied to the anode of the eighth diode, which is connected in parallel between the twenty-seventh and twenty-eighth resistors. The cathode of the eighth diode is connected in parallel to the output terminal of the operational amplifier. The first terminal of the thirtieth resistor is connected to the reference voltage, and the second terminal of the thirtieth resistor is electrically connected to the non-inverting input terminal of the operational amplifier. The first terminal of the thirty-second resistor, the first terminal of the twelfth capacitor, and the first terminal of the thirty-first resistor are connected in parallel to the second terminal of the thirtieth resistor. The second terminal of the thirty-second resistor and the second terminal of the twelfth capacitor are grounded. The second terminal of the thirty-first resistor is connected in parallel to the output terminal of the operational amplifier, and the output terminal of the operational amplifier is electrically connected to the base of the third transistor.

[0013] Furthermore, the switching power supply also includes an undervoltage protection circuit, the input terminal of which is electrically connected to the internal power supply, and the output terminal of which is electrically connected to the base of the third transistor. The undervoltage protection circuit connects the base of the third transistor to the ground terminal when the internal power supply is below the undervoltage threshold.

[0014] Furthermore, the switching power supply also includes an over-temperature protection circuit, the output terminal of which is electrically connected to the base of the third transistor, and the over-temperature protection circuit includes a thermistor. The over-temperature protection circuit outputs a low level to pull down the base potential of the third transistor when the temperature exceeds the high-temperature threshold.

[0015] The advantages and beneficial effects of this invention are as follows: This invention divides the DC bus into multiple sub-DC bus segments through several power-taking contacts in the DC bus, and drives a multi-channel switching circuit with a drive circuit, so that multiple DC bus segments are simultaneously powered through the multi-channel switching circuit. This achieves rapid discharge of the DC bus capacitors after AC power failure, while effectively avoiding problems such as the difficulty of consistent control of direct cascaded drive of the entire bus, the high risk of voltage imbalance due to multi-stage series capacitors of high-voltage electrolytic capacitors, and the influence of high-order harmonics in AC power supply, thus greatly enhancing the reliability of the power supply. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the circuit structure of the switching power supply for the DC bus power draw of the active power filter of the present invention; Figure 2 This is a circuit diagram of a switching power supply for an active power filter that draws power from the DC bus according to the present invention. Figure 3 This is the feedback circuit diagram of the present invention; Figure 4 This is the overvoltage protection circuit diagram of the present invention; Figure 5 This is a short-circuit protection circuit diagram of the present invention; Figure 6 This is the undervoltage protection circuit diagram of the present invention; Figure 7 This is the over-temperature protection circuit diagram of the present invention; Figure 8 This is the overall circuit diagram of the switching power supply for the DC bus power draw of the active power filter of the present invention. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0018] according to Figures 1-8 As shown, the present invention is a switching power supply designed to achieve the above-mentioned objective. The technical solution of the present invention is to design an active power filter DC bus power supply, including: power chip U1, high voltage power-on start-up circuit 101, drive circuit 102, multi-channel switching circuit, first transformer T1 and rectifier filter circuit 103.

[0019] The input terminal of the high-voltage power-on start circuit 101 is electrically connected to the DC bus of the active power filter, and the output terminal of the high-voltage power-on start circuit outputs the internal power supply VCC to power the power chip and the drive circuit.

[0020] The drive circuit 102 includes a push-pull circuit and a second transformer T3. The input terminal of the push-pull circuit is electrically connected to the control signal output pin OUT of the power chip U1, and the output terminal of the push-pull circuit is electrically connected to the primary winding T3A of the second transformer T3. The multiple secondary windings of the second transformer T3 are respectively electrically connected to the control terminal of each switching circuit.

[0021] Each switching circuit is electrically connected to the power take-up contacts of the DC bus and each primary winding of the first transformer T1, and is used to control the circuit connection and disconnection between each segment of the DC bus divided by the power take-up contacts and each primary winding of the first transformer T1 according to the drive signal output by the drive circuit.

[0022] The primary winding T1D of the first transformer T1 is electrically connected to the input terminal of the rectifier and filter circuit, and the output terminal of the rectifier and filter circuit serves as the output of the entire power supply.

[0023] by Figure 1 For example, Figure 1 The switching power supply adopts a simultaneous power supply method using a full DC bus plus a center contact N, avoiding the problem of difficult consistency control caused by direct cascading of the entire bus. The DC bus of the active power filter, divided into two sections by the center contact N, can be considered as two capacitors, denoted by Ca and Cb. Capacitor Ca can be considered the positive half-bus capacitor, and capacitor Cb can be considered the negative half-bus capacitor. Capacitors Ca and Cb are the DC bus capacitors of the active power filter. The capacitance balancing of capacitors C1 and C2 is achieved through the control of the active power filter; it is voltage equalization controlled, not resistive voltage division, thus eliminating the risk of voltage imbalance.

[0024] The DC bus voltage of an active power filter is high. In this case, selecting a single-ended flyback circuit would result in high voltage spikes on the power switching transistors in the circuit, and MOSFETs with such high voltage ratings are expensive on the market. By adopting a method of supplying power to the entire bus and several power-taking contacts simultaneously, the entire bus is divided into multiple DC bus segments for separate control. This bypasses the problem of difficult consistency control when directly cascading the entire bus, and the MOSFETs selected as switching transistors are of common types and inexpensive.

[0025] Combination Figure 1 , Figure 2 The switching power supply achieves high-voltage power-on startup through the high-voltage power-on startup circuit 101. During the initial power-on phase, the high-voltage power-on startup circuit 101 outputs internal power to supply power to internal components, such as the power chip U1 and the transistors of the drive circuit. Figure 1 The example multiplexer circuit includes a first switching circuit 104 and a second switching circuit 105. The first switching circuit 104 controls the on / off connection between the sub-DC bus Ca and the primary winding T1A of transformer T1, and the second switching circuit 105 controls the on / off connection between the sub-DC bus Cb and the primary winding T1B of transformer T1. Figure 2 The push-pull circuit in the drive circuit 102 is composed of transistors Q6 and Q7. When the high-frequency PWM control signal is output from the control signal output pin OUT of the power chip U1, transistors Q6 and Q7 in the push-pull circuit alternately turn on and off. The high-frequency PWM control signal is amplified by transistors Q6 and Q7 and input to the primary winding T3A of the main side of transformer T3, and then transmitted to the two secondary windings T3B and T3C of the secondary side of transformer T3. The control terminals of the first switch circuit 104 and the second switch circuit 105 are respectively connected to the secondary windings T3C and T3B of transformer T3. The secondary windings T3C and T3B output high-frequency pulsating voltage synchronized with the high-frequency PWM control signal to the control terminals of the first switch circuit 104 and the second switch circuit 105, driving the switching of the MOSFETs in the first switch circuit 104 and the second switch circuit 105, thereby controlling the circuit connection between the sub-DC bus Ca and the primary winding T1A of transformer T1, and the circuit connection between the sub-DC bus Cb and the primary winding T1B of transformer T1.

[0026] The DC bus supplies power to multiple primary windings of transformer T1 in segments. The electrical energy is then transferred to the secondary windings via the transformer. After rectification and filtering by the rectifier and filter circuit connected to the secondary windings, the output power VOUT is used as the overall power supply output.

[0027] The switching power supply of this invention achieves high-voltage power-on startup through a high-voltage power-on startup circuit. The drive circuit is driven by two auxiliary windings of the transformer. Because the DC bus is powered in segments through the power-taking contacts, the drive of the multi-channel switching circuit does not need to be completely synchronous. This avoids problems such as the difficulty in controlling drive consistency, the high risk of voltage imbalance due to multi-stage series capacitors of high-voltage electrolytic capacitors, and the influence of high-order harmonics in the AC power supply, thus greatly enhancing the reliability of the power supply.

[0028] To achieve segmented multi-path power supply for the DC bus and avoid problems such as difficulty in controlling drive consistency, high risk of voltage imbalance due to multi-stage series capacitors in high-voltage electrolytic capacitors, and the influence of high-order harmonics in AC power supply, the preferred embodiment of this invention is that, among the power-taking contacts at both ends of each sub-DC bus, the potential of the first power-taking contact is higher than the potential of the second power-taking contact (for example, the electromotive force of the positive contact Vbus+ of sub-DC bus Ca is greater than that of the center contact N1, and the electromotive force of the center contact N1 of sub-DC bus Cb is greater than that of the negative contact Vbus+).

[0029] The multi-channel switching circuit includes a first switching circuit 104, which controls the circuit connection and disconnection between the first sub-DC bus Ca and the first primary winding T1A of the first transformer T1. The first switching circuit includes a first capacitor C1, a first resistor R1, a first diode D2, a first MOSFET Q1, a second diode D3, and a second resistor R7.

[0030] The first terminal of the first capacitor C1, the first terminal of the first resistor R1, and the first terminal of the first primary winding T1A of the first transformer T1 are electrically connected to the first power-taking contact (i.e., the positive contact Vbus+) of the first sub-DC bus. The second terminal of the first capacitor C1 and the second terminal of the first resistor R1 are connected in parallel to the cathode of the first diode D2. The anode of the first diode D2 and the first terminal of the first MOSFET Q1 are connected in parallel to the second terminal of the first primary winding T1A of the first transformer T1. The gate of the first MOSFET Q1 is electrically connected to the first primary winding T3C of the second transformer T3. The second terminal of the first MOSFET Q1 is electrically connected to the second power-taking contact (i.e., the center contact N1) of the first sub-DC bus.

[0031] The circuit structure and connection relationship of each switch circuit are similar to those of the first switch circuit. The working principle of the multi-channel switch circuit is explained below using the first switch circuit 104 and the second switch circuit 105 as examples.

[0032] The high-frequency PWM signal output by power chip U1 is transmitted through transformer T3 to the gates of MOSFETs Q1 and Q3 in the first switching circuit 104 and the second switching circuit 105, controlling the alternating high-frequency switching of MOSFETs Q1 and Q3 (e.g., 10kHz~100kHz). When MOSFET Q1 is on, a loop is formed from the positive contact Vbus+ of the positive half-bus Ca → primary winding T1A → MOSFET Q1 → center contact N, and a high-frequency pulsed DC current flows through the primary winding T1A. When MOSFET Q3 is on, a loop is formed from the center contact N of the negative half-bus Cb → primary winding T1B → MOSFET Q3 → ground, and a high-frequency pulsed DC current flows through the primary winding T1B. The conduction time of the two transistors is adjusted by the PWM duty cycle of the signal output by power chip U1, and there is no fixed limitation on the half-wave period.

[0033] In order to improve the power quality and stability of the switching power supply output, a preferred embodiment of the present invention is that the rectifier filter circuit includes a bidirectional rectifier diode D1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4.

[0034] The anode of the bidirectional rectifier diode D1 is electrically connected to the first terminal of the primary winding T1D of the first transformer T1. The cathode of the bidirectional rectifier diode D1 serves as the positive output terminal of the power supply system. The positive terminals of the second capacitor C2, the third capacitor C3, and the first terminal of the fourth capacitor C4 are connected in parallel to the cathode of the bidirectional rectifier diode D1. The second terminal of the primary winding T1D of the first transformer T1, the negative terminal of the second capacitor C2, the negative terminal of the third capacitor C3, and the second terminal of the fourth capacitor C4 are connected in parallel to ground.

[0035] Bidirectional rectifier diode D1 is used for full-wave rectification. Capacitors C2 and C3 are electrolytic capacitors used for low-frequency filtering. Capacitor C4 is a general-purpose ceramic capacitor used for high-frequency filtering.

[0036] To ensure safe and reliable high-voltage power-on startup, the preferred embodiment of the present invention is that the high-voltage power-on startup circuit includes a third resistor R3, a fourth resistor R6, a fifth resistor R9, a sixth resistor R11, a seventh resistor R14, a second MOSFET Q2, a third MOSFET Q4, a Zener diode ZD1, a third diode D6, a fifth capacitor C6, and a sixth capacitor C7.

[0037] The third resistor R3, the fourth resistor R6, the fifth resistor R9, the sixth resistor R11, and the seventh resistor R14 are connected in series with the cathode of the third diode D6. The anode of the third diode D6 is grounded. One end of the third resistor R3 and the first terminal of the second MOSFET Q2 are connected in parallel to the positive terminal Vbus+ of the DC bus. The second terminal of the second MOSFET Q2 is electrically connected to the first terminal of the third MOSFET Q4. The gate of the second MOSFET Q2 is connected in parallel between the fifth resistor R9 and the sixth resistor R11. The cathode of the Zener diode ZD1 is connected in parallel to the gate of the second MOSFET Q2. The anode of the Zener diode ZD1 is connected in parallel to the second terminal of the second MOSFET Q2. The gate of the third MOSFET Q4 is connected in parallel between the seventh resistor R14 and the third diode D6. The second terminal of the third MOSFET Q4, the first terminal of the fifth capacitor C6, and the first terminal of the sixth capacitor C7 are connected in parallel to the output terminal VCC of the high-voltage power-on start-up circuit. The second terminals of the fifth capacitor C6 and the sixth capacitor C7 are grounded.

[0038] Resistors R3, R6, R9, R11, and R14, connected in series, form a voltage divider network that proportionally reduces the high voltage, providing a safe voltage range for MOSFETs Q2 and Q4 and Zener diode ZD1, while simultaneously controlling the charging rate of filter capacitors C6 and C7. MOSFETs Q2 and Q4 act as electronic switches, controlling the on / off state of the high-voltage power-on startup circuit. During the initial power-on phase, they are turned off, allowing the voltage divider network to charge capacitors C6 and C7 to establish the output of the internal power supply VCC. Zener diode ZD1 has both voltage clamping and threshold control functions, while diode D6 provides overvoltage protection and voltage regulation. Filter capacitors C6 and C7 charge through the voltage divider resistors during power-on, establishing the output of the internal power supply VCC to provide initial power to the power chip, while also acting as a filter to ensure stable power supply.

[0039] In order to reduce the losses of the high-voltage power-on start-up circuit and improve the power supply efficiency of the internal power supply, the preferred embodiment of the present invention is that the switching power supply further includes a winding power supply circuit, which includes a seventh capacitor C8, a fourth diode D7, a first transistor Q5, a fifth diode D8, an eighth resistor R18, an eighth capacitor C9, a ninth capacitor C10, a sixth diode D9, and the second stage winding T1C of the first transformer T1.

[0040] The first terminal of the seventh capacitor C8 and the cathode of the fourth diode D7 are connected in parallel to the output terminal of the high-voltage power-on starting circuit. The anode of the fourth diode D7 is electrically connected to the first terminal of the first transistor Q5. The second terminal of the first transistor Q5 is electrically connected to the first terminal of the eighth capacitor C9 and the cathode of the fifth diode D8. The base of the first transistor Q5 is electrically connected to the cathode of the sixth diode D9. The anode of the fifth diode D8 is electrically connected to the first terminal of the second winding T1C of the first transformer T1. The second terminal of the second winding T1C of the first transformer T1, the second terminal of the eighth capacitor C9, the anode of the sixth diode D9, and the second terminal of the seventh capacitor C8 are grounded. The eighth resistor R18 is connected in parallel between the second terminal and the base of the first transistor Q5. The ninth capacitor C10 is connected in parallel across the six diode D9.

[0041] The winding power supply circuit is used to output the internal power supply VCC to power the power chip and drive circuit after the high-voltage power-on start circuit is powered on and started, and to cut off the output of the high-voltage power-on start circuit.

[0042] After the power-on startup phase of the high-voltage power-on circuit, the internal power supply VCC is output through the winding power supply circuit during normal operation. At this time, the winding power supply circuit pulls up the source voltage of MOSFET Q4 in the high-voltage power-on circuit. When the gate voltage of MOSFET Q4 is lower than the source voltage, MOSFET Q4 is automatically turned off, thereby cutting off the output of the high-voltage power-on circuit.

[0043] In this circuit, diodes D7 and D8 provide rectification, while transistor Q5 acts as a switch to control the power supply to the secondary winding T1C, achieving pulse control for power on and power off. Diode D9 clamps the reverse electromotive force to prevent damage to the transistor from the induced high voltage in the winding when Q5 is off. Resistor R18 provides bias and current limiting. Capacitors C8, C9, and C10 provide filtering and also form a freewheeling circuit when Q5 is off, releasing the remaining energy in winding T1C.

[0044] To achieve feedback regulation and ensure stable overall power output, a preferred embodiment of the present invention further includes a feedback circuit in the switching power supply. The feedback circuit includes a ninth resistor R27, a tenth resistor R30, an eleventh resistor R31, a twelfth resistor R29, a tenth capacitor C19, a first reference voltage source IC1, a first optocoupler U2, a thirteenth resistor R26, a fourteenth resistor R28, a fifteenth resistor R25, and a second transistor Q10.

[0045] The first terminal of the ninth resistor R27 and the first terminal of the tenth resistor R30 are connected in parallel to the output terminal of the rectifier filter circuit. The second terminal of the ninth resistor R27 is electrically connected to the anode of the first optocoupler U2. The second terminal of the tenth resistor R30 is electrically connected to the first terminal of the eleventh resistor R31. The reference electrode of the first reference voltage source IC1 is connected in parallel between the tenth resistor R30 and the eleventh resistor R31. The cathode of the first reference voltage source IC1 is electrically connected to the cathode of the first optocoupler U2. The anode of the first reference voltage source IC1 and the second terminal of the eleventh resistor R31 are grounded. The tenth capacitor C19 is connected in parallel between the anode and the reference electrode of the first reference voltage source IC1. The twelfth resistor R29 is connected in parallel between the anode and cathode of the first optocoupler U2. The collector of the first optocoupler U2 is connected in parallel to the first terminal of the thirteenth resistor R26 and the first terminal of the fourteenth resistor R28. The emitter of the first optocoupler U2 is grounded. The second terminal of the thirteenth resistor R26 is electrically connected to the reference voltage pin VREF of the power supply chip U1. The second terminal of the fourteenth resistor R28 is electrically connected to the base of the second transistor Q10. The emitter of the second transistor Q10 is electrically connected to the compensation pin COMP of the power supply chip U1. The collector of the second transistor Q10 is grounded. The fifteenth resistor R25 is connected in parallel between the base and emitter of the second transistor Q10. The second transistor is a PNP transistor.

[0046] In this circuit, resistors R27, R29, R30, and R31 form a voltage divider network to sample the output voltage Vout of the switching power supply. Capacitor C19 acts as a filter capacitor to stabilize the feedback voltage. The reference voltage source IC1 (such as TL431) compares the feedback voltage with an internal reference, controlling the current on one side of the optocoupler U2's photodiode. Optocoupler U2 provides electrical isolation, preventing high voltage interference from the input side to the output side, while simultaneously transmitting the feedback signal. Transistor Q10 and resistors R25 and R28 form a signal amplification circuit to ensure feedback accuracy. The switching power supply output voltage Vout is divided by the voltage divider resistors and then input to the reference terminal of the reference voltage source IC1. The reference voltage source IC1 adjusts the cathode current based on the deviation between the divided voltage and the internal reference, thereby changing the luminous intensity of the photodiode in optocoupler U2. When the transistor side of optocoupler U2 is turned on, the reference voltage VREF forms a ground path through the transistor side of optocoupler U2, which pulls down the base potential of transistor Q10. The emitter potential of transistor Q10 rises, affecting the COMP pin of power chip U1. Power chip U1 adjusts the PWM output duty cycle accordingly to achieve stable regulation of the output voltage.

[0047] To achieve overvoltage protection of the switching power supply output and improve the safety of the switching power supply, a preferred embodiment of the present invention is that the switching power supply further includes an overvoltage protection circuit and a third transistor Q9. The overvoltage protection circuit includes a sixteenth resistor R34, a seventeenth resistor R37, an eighteenth resistor R39, a nineteenth resistor R36, a second reference voltage source IC2, a second optocoupler U3, a twentieth resistor R33, a twenty-first resistor R38, and a fourth MOSFET Q13.

[0048] The first terminals of the sixteenth resistor R34 and the seventeenth resistor R37 are connected in parallel to the output of the rectifier filter circuit. The second terminal of the sixteenth resistor R34 is electrically connected to the anode of the second optocoupler U3. The second terminal of the seventeenth resistor R37 is electrically connected to the first terminal of the eighteenth resistor R39. The reference electrode of the second reference voltage source IC2 is connected in parallel between the seventeenth resistor R37 and the eighteenth resistor R39. The cathode of the second reference voltage source IC2 is electrically connected to the cathode of the second optocoupler U3. The anode of the second reference voltage source IC2 and the second terminal of the eighteenth resistor R39 are grounded. The nineteenth resistor R36 is connected in parallel between the anode and cathode of the second optocoupler U3. The collector of the second optocoupler U3... The emitter of the second optocoupler U3 is electrically connected to the first terminal of the twentieth resistor R33, and the second terminal of the twentieth resistor R33 is electrically connected to the reference voltage pin VREF of the power supply chip U1. The emitter of the second optocoupler U3 is electrically connected to the gate of the fourth MOSFET Q13, and the source of the fourth MOSFET Q13 is grounded. The twenty-first resistor R38 is connected in parallel between the gate and source of the fourth MOSFET. The drain of the fourth MOSFET Q13 is electrically connected to the base of the third transistor Q9, and the emitter of the third transistor Q9 is electrically connected to the compensation pin COMP of the power supply chip U1. The collector of the third transistor Q9 is grounded, and the base of the third transistor Q9 is connected in parallel to the reference voltage pin VREF of the power supply chip U1. The third transistor Q9 is a PNP transistor, and the fourth MOSFET Q13 is an NMOS transistor.

[0049] Similar to the diode side circuit of the optocoupler in the feedback circuit, resistors R34, R37, R39, and R36 form a voltage divider network to sample the output voltage Vout of the switching power supply. The reference voltage source IC2 is used to compare the feedback voltage with the internal reference and control the current on the diode side of optocoupler U3. When the output voltage Vout of the switching power supply is overvoltage, the photodiode of optocoupler U3 is activated, controlling the transistor side of optocoupler U3 to conduct, forming a connection path from the reference voltage VREF to the gate of MOSFET Q13. This pulls up the gate potential of MOSFET Q13, turning on MOSFET Q13. The reference voltage VREF connected to the base of transistor Q9 forms a ground path through MOSFET Q13, pulling down the base potential of transistor Q9. The emitter potential of transistor Q9 rises and is fed back to the COMP pin of power chip U1, triggering power chip U1 to turn off, thus achieving overvoltage protection.

[0050] To achieve short-circuit protection of the switching power supply output and improve the safety of the switching power supply, a preferred embodiment of the present invention further includes a short-circuit protection circuit, which includes resistors R45 (22nd), R49 (23rd), R52 (24th), R48 (25th), IC3 (3rd reference voltage source), U5 (3rd optocoupler), R47 (26th), R44 (27th), R41 (28th), R46 (29th), R43 (30th), R50 (31st), R51 (32nd), C23 (11th), C24 (12th), D14 (7th), D13 (8th), and U4 (operational amplifier).

[0051] The first terminal of the twenty-second resistor R45 and the first terminal of the twenty-third resistor R49 are connected in parallel to the output terminal of the rectifier filter circuit. The second terminal of the twenty-second resistor R45 is electrically connected to the anode of the third optocoupler U5. The second terminal of the twenty-third resistor R49 is electrically connected to the first terminal of the twenty-fourth resistor R52. The reference electrode of the third reference voltage source IC3 is connected in parallel between the twenty-third resistor R49 and the twenty-fourth resistor R52. The cathode of the third reference voltage source IC3 is electrically connected to the cathode of the third optocoupler U5. The anode of the third reference voltage source IC3 and the twenty-fourth resistor R52 are connected in parallel. The second terminal of R52 is grounded. The twenty-fifth resistor R48 is connected in parallel between the anode and cathode of the third optocoupler U5. The collector of the third optocoupler U5 is electrically connected to the first terminal of the twenty-sixth resistor R47, and the emitter of the third optocoupler U5 is grounded. The second terminal of the twenty-sixth resistor R47 is electrically connected to the first terminal of the twenty-ninth resistor R46. The first terminal of the eleventh capacitor C23 is connected in parallel between the twenty-sixth resistor R47 and the twenty-ninth resistor R46. The second terminal of the eleventh capacitor C23 is grounded. The second terminal of the twenty-ninth resistor R46 is connected to the inverting output of the operational amplifier U4. The input terminals are electrically connected as follows: the cathode of the seventh diode D14 and the first terminal of the twenty-seventh resistor R44 are connected in parallel between the twenty-sixth resistor R47 and the twenty-ninth resistor R46; the anode of the seventh diode D14 and the second terminal of the twenty-seventh resistor R44 are connected in parallel between the first terminal of the twenty-eighth resistor R41; the second terminal of the twenty-eighth resistor R41 is connected to the reference voltage +5V; the anode of the eighth diode D13 is connected in parallel between the twenty-seventh resistor R44 and the twenty-eighth resistor R41; and the cathode of the eighth diode D13 is connected in parallel to the output terminal of operational amplifier U4. The thirtieth... The first terminal of resistor R43 is connected to the reference voltage +5V. The second terminal of the thirtieth resistor R43 is electrically connected to the non-inverting input terminal of operational amplifier U4. The first terminal of the thirty-second resistor R51, the first terminal of the twelfth capacitor C24, and the first terminal of the thirty-first resistor R50 are connected in parallel to the second terminal of the thirtieth resistor R43. The second terminals of the thirty-second resistor R51 and the second terminal of the twelfth capacitor C24 are grounded. The second terminal of the thirty-first resistor R50 is connected in parallel to the output terminal of operational amplifier U4. The output terminal of operational amplifier U4 is electrically connected to the base of the third transistor Q9.

[0052] When the output voltage Vout of the switching power supply is short-circuited, the output voltage Vout drops sharply. The optocoupler, which was originally activated by the output voltage Vout through resistors R45, R49, R52, R48 and the reference voltage source IC3, is cut off. The reference voltage +5V is pulled high at the inverting terminal of the operational amplifier U4 through diode D14, and the output terminal of the operational amplifier U4 is pulled low, thereby pulling down the base potential of transistor Q9. The emitter potential of transistor Q9 rises and is fed back to the COMP pin of the power chip U1, triggering the power chip U1 to turn off, thus achieving short-circuit protection.

[0053] To achieve undervoltage protection of the internal power supply and improve the safety of the switching power supply, a preferred embodiment of the present invention is that the switching power supply further includes an undervoltage protection circuit. The input terminal of the undervoltage protection circuit is electrically connected to the internal power supply VCC, and the output terminal of the undervoltage protection circuit is electrically connected to the base of the third transistor Q9. When the internal power supply VCC is lower than the undervoltage threshold, the undervoltage protection circuit connects the base of the third transistor Q9 to the ground terminal.

[0054] When the internal power supply VCC is higher than the undervoltage threshold, the Zener diode D12 breaks down, the gate potential of MOSFET Q12 is pulled high, and MOSFET Q12 conducts, thereby pulling down the gate voltage of MOSFET Q11. MOSFET Q11 is then turned off, and the base potential of transistor Q9 remains at the reference voltage VREF, without triggering undervoltage protection. When the internal power supply VCC is lower than the undervoltage threshold, the Zener diode D12 is turned off, the gate potential of MOSFET Q11 is pulled high, and MOSFET Q11 conducts. The base potential of transistor Q9 is pulled low, and the emitter potential of transistor Q9 rises, feeding back to the COMP pin of power chip U1, triggering power chip U1 to turn off, thus achieving undervoltage protection.

[0055] To improve the safety of the switching power supply by providing over-temperature protection, a preferred embodiment of the present invention further includes an over-temperature protection circuit. The output terminal of the over-temperature protection circuit is electrically connected to the base of the third transistor Q9. The over-temperature protection circuit includes a thermistor RT1. When the temperature exceeds the high-temperature threshold, the over-temperature protection circuit outputs a low level to pull down the base potential of the third transistor Q9.

[0056] The higher the temperature of the thermistor RT1, the lower its resistance. The temperature control chip J1 compares the input voltage with its internal reference threshold and outputs high and low level control signals. R40 and R42 are voltage divider resistors, and C20 is a filter capacitor. When the temperature is too high, the resistance of the thermistor RT1 becomes less than the threshold, causing the reference voltage VREF to be divided and the voltage at the input of the temperature control chip J1 to be less than the internal reference threshold. This results in a low-level signal outputting a low base potential of the transistor Q9, triggering the power supply chip U1 to turn off, thus achieving over-temperature protection.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A switching power supply that draws power from the DC bus of an active power filter, characterized in that, include: Power supply chip, high-voltage power-on start-up circuit, drive circuit, multiplexer circuit, first transformer and rectifier filter circuit; The input terminal of the high-voltage power-on start-up circuit is electrically connected to the DC bus of the active power filter, and the output terminal of the high-voltage power-on start-up circuit outputs internal power to power the power chip and the drive circuit. The drive circuit includes a push-pull circuit and a second transformer. The input terminal of the push-pull circuit is electrically connected to the control signal output pin of the power chip, and the output terminal of the push-pull circuit is electrically connected to the primary winding of the second transformer. The multiple secondary windings of the second transformer are respectively electrically connected to the control terminal of each switching circuit. Each switching circuit is electrically connected to the power take-up contacts of the DC bus and each primary winding of the first transformer, respectively, and is used to control the circuit connection and disconnection between each segment of the DC bus divided by the power take-up contacts and each primary winding of the first transformer according to the drive signal output by the drive circuit. The primary winding of the first transformer is electrically connected to the input terminal of the rectifier and filter circuit, and the output terminal of the rectifier and filter circuit serves as the output of the entire power supply.

2. The switching power supply according to claim 1, characterized in that, In each DC bus section, the potential of the first power-taking contact is higher than that of the second power-taking contact. The multi-channel switching circuit includes a first switching circuit, which controls the circuit connection and disconnection between the first sub-DC bus and the first primary winding of the first transformer. The first switching circuit includes a first capacitor, a first resistor, a first diode, a first MOSFET, a second diode, and a second resistor. The first terminal of the first capacitor, the first terminal of the first resistor, and the first terminal of the first primary winding of the first transformer are electrically connected to the first power-taking contact of the first sub-DC bus. The second terminal of the first capacitor and the second terminal of the first resistor are connected in parallel to the cathode of the first diode. The anode of the first diode and the first terminal of the first MOSFET are connected in parallel to the second terminal of the first primary winding of the first transformer. The gate of the first MOSFET is electrically connected to the first primary winding of the second transformer. The second terminal of the first MOSFET is electrically connected to the second power-taking contact of the first sub-DC bus.

3. The switching power supply according to claim 1, characterized in that, The rectifier and filter circuit includes a bidirectional rectifier diode, a second capacitor, a third capacitor, and a fourth capacitor; The anode of the bidirectional rectifier diode is electrically connected to the first end of the primary winding of the first transformer. The cathode of the bidirectional rectifier diode serves as the positive output terminal of the power supply system. The positive terminals of the second capacitor, the third capacitor, and the fourth capacitor are connected in parallel to the cathode of the bidirectional rectifier diode. The second end of the primary winding of the first transformer, the negative terminal of the second capacitor, the negative terminal of the third capacitor, and the second end of the fourth capacitor are connected in parallel to ground.

4. The switching power supply according to claim 1, characterized in that, The high-voltage power-on start-up circuit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a second MOSFET, a third MOSFET, a Zener diode, a third diode, a fifth capacitor, and a sixth capacitor. The third, fourth, fifth, sixth, and seventh resistors are connected in series with the cathode of the third diode. The anode of the third diode is grounded. One end of the third resistor and the first terminal of the second MOSFET are connected in parallel to the positive terminal contact of the DC bus. The second terminal of the second MOSFET is electrically connected to the first terminal of the third MOSFET. The gate of the second MOSFET is connected in parallel between the fifth and sixth resistors. The cathode of the Zener diode is connected in parallel to the gate of the second MOSFET. The anode of the Zener diode is connected in parallel to the second terminal of the second MOSFET. The gate of the third MOSFET is connected in parallel between the seventh resistor and the third diode. The second terminal of the third MOSFET, the first terminal of the fifth capacitor, and the first terminal of the sixth capacitor are connected in parallel to the output terminal of the high-voltage power-on start-up circuit. The second terminals of the fifth and sixth capacitors are grounded.

5. The switching power supply according to claim 1, characterized in that, The switching power supply also includes a winding power supply circuit, which includes a seventh capacitor, a fourth diode, a first transistor, a fifth diode, an eighth resistor, an eighth capacitor, a ninth capacitor, a sixth diode, and the second stage winding of the first transformer. The first terminal of the seventh capacitor and the cathode of the fourth diode are connected in parallel to the output terminal of the high-voltage power-on starting circuit. The anode of the fourth diode is electrically connected to the first terminal of the first transistor. The second terminal of the first transistor is electrically connected to the first terminal of the eighth capacitor and the cathode of the fifth diode. The base of the first transistor is electrically connected to the cathode of the sixth diode. The anode of the fifth diode is electrically connected to the first terminal of the second winding of the first transformer. The second terminal of the second winding of the first transformer, the second terminal of the eighth capacitor, the anode of the sixth diode, and the second terminal of the seventh capacitor are grounded. The eighth resistor is connected in parallel between the second terminal and the base of the first transistor. The ninth capacitor is connected in parallel across the six diodes. The winding power supply circuit is used to output the internal power supply to power the power chip and the drive circuit after the high-voltage power-on start circuit is powered on, and to cut off the output of the high-voltage power-on start circuit.

6. The switching power supply according to claim 1, characterized in that, The switching power supply also includes a feedback circuit, which includes a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a tenth capacitor, a first reference voltage source, a first optocoupler, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, and a second transistor. The first end of the ninth resistor and the first end of the tenth resistor are connected in parallel to the output terminal of the rectifier filter circuit. The second end of the ninth resistor is electrically connected to the anode of the first optocoupler. The second end of the tenth resistor is electrically connected to the first end of the eleventh resistor. The reference electrode of the first reference voltage source is connected in parallel between the tenth and eleventh resistors. The cathode of the first reference voltage source is electrically connected to the cathode of the first optocoupler. The anode of the first reference voltage source and the second end of the eleventh resistor are grounded. The tenth capacitor is connected in parallel between the anode and the reference electrode of the first reference voltage source. The twelfth resistor is connected in parallel between the anode and the cathode of the first optocoupler. The collector of the first optocoupler is connected in parallel to the first end of the thirteenth resistor and the first end of the fourteenth resistor. The emitter of the first optocoupler is grounded. The second end of the thirteenth resistor is electrically connected to the reference voltage pin of the power chip. The second end of the fourteenth resistor is electrically connected to the base of the second transistor. The emitter of the second transistor is electrically connected to the compensation pin of the power chip. The collector of the second transistor is grounded. The fifteenth resistor is connected in parallel between the base and the emitter of the second transistor. The second transistor is a PNP transistor.

7. The switching power supply according to claim 1, characterized in that, The switching power supply also includes an overvoltage protection circuit and a third transistor. The overvoltage protection circuit includes a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a second reference voltage source, a second optocoupler, a twentieth resistor, a twenty-first resistor, and a fourth MOSFET. The first terminals of the sixteenth resistor and the seventeenth resistor are connected in parallel to the output terminal of the rectifier filter circuit. The second terminal of the sixteenth resistor is electrically connected to the anode of the second optocoupler. The second terminal of the seventeenth resistor is electrically connected to the first terminal of the eighteenth resistor. The reference electrode of the second reference voltage source is connected in parallel between the seventeenth and eighteenth resistors. The cathode of the second reference voltage source is electrically connected to the cathode of the second optocoupler. The anode of the second reference voltage source and the second terminal of the eighteenth resistor are grounded. The nineteenth resistor is connected in parallel between the anode and cathode of the second optocoupler. The collector is electrically connected to the first end of the twentieth resistor, the second end of the twentieth resistor is electrically connected to the reference voltage pin of the power supply chip, the emitter of the second optocoupler is electrically connected to the gate of the fourth MOSFET, the source of the fourth MOSFET is grounded, the twentieth eleventh resistor is connected in parallel between the gate and source of the fourth MOSFET, the drain of the fourth MOSFET is electrically connected to the base of the third transistor, the emitter of the third transistor is electrically connected to the compensation pin of the power supply chip, the collector of the third transistor is grounded, and the base of the third transistor is connected in parallel to the reference voltage pin of the power supply chip. The third transistor is a PNP transistor, and the fourth MOSFET is an NMOS transistor.

8. The switching power supply according to claim 7, characterized in that, The switching power supply also includes a short-circuit protection circuit, which includes a 22nd resistor, a 23rd resistor, a 24th resistor, a 25th resistor, a third reference voltage source, a third optocoupler, a 26th resistor, a 27th resistor, a 28th resistor, a 29th resistor, a 30th resistor, a 31st resistor, a 32nd resistor, an 11th capacitor, a 12th capacitor, a 7th diode, an 8th diode, and an operational amplifier. The first end of the 22nd resistor and the first end of the 23rd resistor are connected in parallel to the output terminal of the rectifier filter circuit. The second end of the 22nd resistor is electrically connected to the anode of the third optocoupler. The second end of the 23rd resistor is electrically connected to the first end of the 24th resistor. The reference electrode of the third reference voltage source is connected in parallel between the 23rd resistor and the 24th resistor. The cathode of the third reference voltage source is electrically connected to the cathode of the third optocoupler. The anode of the third reference voltage source and the second end of the 24th resistor are grounded. The 25th resistor is connected in parallel between the anode and the cathode of the third optocoupler. The collector of the third optocoupler is electrically connected to the first terminal of the 26th resistor, the emitter of the third optocoupler is grounded, the second terminal of the 26th resistor is electrically connected to the first terminal of the 29th resistor, the first terminal of the 11th capacitor is connected in parallel between the 26th and 29th resistors, the second terminal of the 11th capacitor is grounded, the second terminal of the 29th resistor is electrically connected to the inverting input terminal of the operational amplifier, the cathode of the 7th diode and the first terminal of the 27th resistor are connected in parallel between the 26th and 29th resistors, the anode of the 7th diode and the second terminal of the 27th resistor are connected in parallel to the first terminal of the 28th resistor, and the second terminal of the 28th resistor is... The reference voltage is applied to the anode of the eighth diode, which is connected in parallel between the twenty-seventh and twenty-eighth resistors. The cathode of the eighth diode is connected in parallel to the output terminal of the operational amplifier. The first terminal of the thirtieth resistor is connected to the reference voltage, and the second terminal of the thirtieth resistor is electrically connected to the non-inverting input terminal of the operational amplifier. The first terminal of the thirty-second resistor, the first terminal of the twelfth capacitor, and the first terminal of the thirty-first resistor are connected in parallel to the second terminal of the thirtieth resistor. The second terminal of the thirty-second resistor and the second terminal of the twelfth capacitor are grounded. The second terminal of the thirty-first resistor is connected in parallel to the output terminal of the operational amplifier, and the output terminal of the operational amplifier is electrically connected to the base of the third transistor.

9. The switching power supply according to claim 7, characterized in that, The switching power supply also includes an undervoltage protection circuit, the input terminal of which is electrically connected to the internal power supply, and the output terminal of which is electrically connected to the base of the third transistor. The undervoltage protection circuit connects the base of the third transistor to the ground terminal when the internal power supply is below the undervoltage threshold.

10. The switching power supply according to claim 7, characterized in that, The switching power supply also includes an over-temperature protection circuit, the output terminal of which is electrically connected to the base of the third transistor, and the over-temperature protection circuit includes a thermistor. The over-temperature protection circuit outputs a low level to pull down the base potential of the third transistor when the temperature exceeds the high-temperature threshold.

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