Control circuit of switching power supply

Abstract

The utility model discloses a control circuit of a switching power supply, which comprises a PWM (Pulse Width Modulation) generator, a first control circuit and a second control circuit, and the PWM signal output end of the PWM generator is connected with the PWM signal input end of a main circuit power conversion module; the first control circuit comprises a switching signal generation circuit and a closed-loop monitoring and short-circuit protection circuit, and the second control circuit comprises a PWM generator power supply control circuit; the input end of the PWM generator power supply control circuit is connected with a PWM generator power supply, and the output end is connected with the power supply input end of the PWM generator; the control end of the PWM generator power supply control circuit is connected with the switching signal output end of the switching signal generation circuit, and the input end of the switching signal generation circuit is connected with an external direct-current power supply; the input end of the closed-loop monitoring and short-circuit protection circuit is connected with the DC output end of the main circuit, and the output end is connected with the control end of the switching signal generation circuit. The control circuit can improve the reliability of the switching power supply and prevent the switching power supply from being damaged due to repeated starting.

Description

[Technical field]

[0001] This utility model relates to high-frequency switching power supplies, and more particularly to a control circuit for a switching power supply. [Background Technology]

[0002] In a conventional switching power supply, the VCC pin level of the switching power supply chip is usually obtained by charging the power supply capacitor through the primary auxiliary winding of the main transformer via diodes and the bus voltage.

[0003] The invention disclosed in application number 201610817811.X is a two-transistor forward converter circuit, including a two-transistor forward network on the primary side of the transformer, a current-doubling rectifier circuit on the secondary side, and a feedback loop. In the primary-side forward converter circuit, losses are reduced by adding an auxiliary winding to power the control chip. The use of a current-doubling rectifier circuit on the secondary side reduces the inductor current by half, making the circuit suitable for high-current applications and avoiding pulse spikes caused by the two diode circuits on the secondary side. In the feedback loop, a soft-start circuit is used to reduce the feedback error at the moment of power-on, allowing the duty cycle to rise slowly and improving circuit stability.

[0004] This invention's chip power supply method suffers from low reliability and is prone to malfunction. Because it lacks undervoltage protection, it enters a "hiccup" state when a short circuit occurs. This "hiccup" state is commonly referred to as "self-oscillation" or "repeated start-up state." This state means that under output short circuit or overload conditions, the power supply cannot operate stably, causing the switching transistor to periodically turn on and off, resulting in unstable output voltage or even failure to output normal voltage. This phenomenon not only affects the reliability of the switching power supply but can also easily damage it if the short circuit period is long. [Utility Model Content]

[0005] The technical problem to be solved by this utility model is to provide a switching power supply control circuit that can improve the reliability of switching power supplies.

[0006] To solve the above-mentioned technical problems, the present invention adopts a control circuit for a switching power supply, comprising a PWM generator, a first control circuit, and a second control circuit. The switching power supply includes a main circuit, which includes a DC input terminal, a power conversion module, and a DC output terminal. The PWM signal output terminal of the PWM generator is connected to the PWM signal input terminal of the power conversion module. The first control circuit includes a switch signal generation circuit and a closed-loop monitoring and short-circuit protection circuit. The second control circuit includes a PWM generator power supply control circuit. The input terminal of the PWM generator power supply control circuit is connected to the PWM generator power supply, and the output terminal is connected to the power input terminal of the PWM generator. The control terminal of the PWM generator power supply control circuit is connected to the switch signal output terminal of the switch signal generation circuit, and the input terminal of the switch signal generation circuit is connected to an external DC power supply. The input terminal of the closed-loop monitoring and short-circuit protection circuit is connected to the DC output terminal of the main circuit, and the output terminal is connected to the control terminal of the switch signal generation circuit.

[0007] The control circuit of the switching power supply described above includes a switching signal generation circuit comprising a second optocoupler, a first voltage divider circuit, and a fourth electrolytic capacitor. The positive terminal of the fourth electrolytic capacitor is connected to the positive terminal of the external DC power supply, the negative terminal of the fourth electrolytic capacitor is connected to the first terminal of the first voltage divider circuit, and the second terminal of the first voltage divider circuit is connected to the negative terminal of the external DC power supply. The anode of the second optocoupler's LED is connected to the voltage signal output terminal of the first voltage divider circuit, and the cathode is connected to the second terminal of the first voltage divider circuit. The collector of the second optocoupler's phototransistor is connected to the control level, and the emitter is connected to the switching signal output terminal of the switching signal generation circuit. The closed-loop monitoring and short-circuit protection circuit includes a second voltage divider circuit and a first optocoupler. The second voltage divider circuit is connected between the positive and negative terminals of the DC output terminal. The voltage signal output terminal of the second voltage divider circuit is connected to the anode of the first optocoupler's LED, and the cathode of the first optocoupler's LED is connected to the negative terminal of the DC output terminal. The collector of the first optocoupler's phototransistor is connected to the positive terminal of the fourth electrolytic capacitor, and the emitter is connected to the negative terminal of the fourth electrolytic capacitor.

[0008] The control circuit of the switching power supply described above includes a closed-loop monitoring and short-circuit protection circuit comprising a third Zener diode, the anode of which is connected to the anode of the first optocoupler LED, and the cathode of which is connected to the voltage signal output terminal of the second voltage divider circuit. The switching signal generation circuit includes a fourth Zener diode, a tenth capacitor, a seventeenth resistor, and an eleventh capacitor. The anode of the fourth Zener diode is connected to the negative terminal of the external DC power supply, and the cathode is connected to the cathode of the second optocoupler LED. The fourth Zener diode and the tenth capacitor are connected in parallel with the external DC power supply, and the eleventh capacitor is connected in parallel with the cathode of the second optocoupler LED.

[0009] The control circuit of the switching power supply described above includes a fourth NPN transistor, a PMOS transistor, a twentieth resistor, and a twenty-first resistor. The source of the PMOS transistor is connected to the positive terminal of the PWM generator power supply, and the power input terminal of the PWM generator is connected to the drain of the PMOS transistor. The collector of the fourth NPN transistor is connected to the power input terminal of the PWM generator through the twenty-first resistor, and to the gate of the PMOS transistor through the twentieth resistor. The base of the fourth NPN transistor is connected to the switch signal output terminal of the switch signal generation circuit, and the emitter is connected to the negative terminal of the DC input terminal.

[0010] The control circuit of the switching power supply described above includes a thermistor, a 12th capacitor, a 13th capacitor, a 5th electrolytic capacitor, a 22nd resistor, and a 23rd resistor. The source of the PMOS transistor is connected to the positive terminal of the PWM generator power supply through the thermistor and to the negative terminal of the DC input through the 5th electrolytic capacitor. The base of the fourth NPN transistor is connected to the switch signal output terminal of the switch signal generation circuit through the 23rd resistor and to the negative terminal of the DC input through the 22nd resistor. The 13th capacitor and the 22nd resistor are connected in parallel. The drain of the PMOS transistor is connected to the negative terminal of the DC input through the 12th capacitor.

[0011] The control circuit of the switching power supply described above includes a main circuit comprising a main transformer and a secondary output circuit of the main transformer. The power conversion module includes a primary circuit of the main transformer, a push-pull drive circuit, and a PWM generator power supply circuit. The primary circuit of the main transformer is connected to the primary winding of the main transformer, the secondary output circuit of the main transformer is connected to the secondary winding of the main transformer, and the power supply circuit of the PWM generator is connected to the primary auxiliary winding of the main transformer. The output terminal of the power supply circuit of the PWM generator is the power supply for the PWM generator.

[0012] The control circuit of the switching power supply described above includes a primary circuit of the main transformer comprising a first MOSFET, a second MOSFET, a sampling resistor, a first clamping diode, a second clamping diode, a first Zener diode, and a second Zener diode. The source of the first MOSFET and the cathode of the first clamping diode are connected to the same-name terminals of the primary winding of the main transformer. The drain of the first MOSFET is connected to the positive terminal of the DC input and the first terminal of the sixth capacitor. The anode of the first clamping diode is connected to the negative terminal of the DC input. The cathode of the second clamping diode is connected to the drain of the first MOSFET, and the anode is connected to the drain of the second MOSFET. The drain of the second MOSFET is connected to the opposite-name terminal of the primary winding. The source of the second MOSFET is connected to the second terminal of the sixth capacitor and connected to the negative terminal of the DC input through the sampling resistor. A fourth capacitor is connected in parallel across the sampling resistor. The DC input includes a current-limiting resistor and a first electrolytic capacitor. The first terminal of the current-limiting resistor is connected to the positive terminal of the DC input and the first terminal is connected to the output terminal of the control level. A fifth capacitor, the first electrolytic capacitor, and an eighth resistor are connected in parallel between the positive and negative terminals of the DC input.

[0013] The control circuit of the switching power supply described above, the push-pull drive circuit includes a first resistor, a second resistor, a first NPN transistor, a PNP transistor, a first diode, a second diode, a first capacitor, and a push-pull transformer. The first end of the first resistor is connected to the PWM signal output terminal of the PWM generator, and the second end of the first resistor is connected to the base of the first NPN transistor and the base of the PNP transistor, respectively. The collector of the first NPN transistor and the cathode of the first diode are respectively connected to the output terminal of the control level. The emitter of the first NPN transistor is connected to the emitter of the PNP transistor, the anode of the first diode, and the cathode of the second diode, respectively, and is connected to the same-name terminal of the primary winding of the push-pull transformer via the second resistor and the first capacitor connected in series. The collector of the PNP transistor is connected to the anode of the second diode and the negative terminal of the DC input terminal, and is connected to the opposite-name terminal of the primary winding of the push-pull transformer. The push-pull transformer includes two secondary windings. The gate of the first MOSFET is connected to the first secondary winding of the push-pull transformer via a fourth resistor and a second capacitor. The source of the first MOSFET is connected to the opposite terminal of the first secondary winding of the push-pull transformer; the cathode of the first Zener diode is connected to the gate of the first MOSFET, and the anode of the first Zener diode is connected to the source of the first MOSFET; the ninth resistor is connected in parallel with the first Zener diode; the anode of the third diode is connected to the gate of the first MOSFET, and the cathode of the third diode is connected to the first terminal of the third resistor; the second terminal of the third resistor is connected to the connection point of the fourth resistor and the second capacitor; the gate of the second MOSFET is connected to the same terminal of the second secondary winding of the push-pull transformer via the sixth resistor and the third capacitor, and the source of the second MOSFET is connected to the opposite terminal of the first secondary winding of the push-pull transformer; the cathode of the second Zener diode is connected to the gate of the second MOSFET, and the anode of the second Zener diode is connected to the source of the second MOSFET; the tenth resistor is connected in parallel with the second Zener diode; the anode of the fourth diode is connected to the gate of the second MOSFET, and the cathode of the fourth diode is connected to the first terminal of the fifth resistor; the second terminal of the fifth resistor is connected to the connection point of the sixth resistor and the third capacitor.

[0014] The control circuit of the switching power supply described above includes an output rectifier diode, a freewheeling diode, an output filter electrolytic capacitor, an energy storage inductor, a thirteenth resistor, a fourteenth resistor, an eighth capacitor, a ninth capacitor, and a load resistor. The anode of the output rectifier diode is connected to the same-name terminal of the secondary winding of the main transformer, and the opposite-name terminal of the secondary winding of the main transformer is connected to the negative terminal of the DC output terminal. The cathode of the output rectifier diode is connected to the positive terminal of the DC output terminal through the energy storage inductor. The positive terminal of the output filter electrolytic capacitor and the first terminal of the load resistor are connected to the positive terminal of the DC output terminal. The anode of the freewheeling diode, the negative terminal of the output filter electrolytic capacitor, and the second terminal of the load resistor are connected to the negative terminal of the DC output terminal. The cathode of the freewheeling diode is connected to the cathode of the output rectifier diode. The thirteenth resistor and the eighth capacitor are connected in series and then in parallel with the output rectifier diode. The fourteenth resistor and the ninth capacitor are connected in series and then in parallel with the freewheeling diode.

[0015] The control circuit of the switching power supply described above, and the power supply circuit of the PWM generator, include an eleventh resistor, a twelfth resistor, a seventh capacitor, a seventh diode, and a second electrolytic capacitor. The anode of the seventh capacitor is connected to the same-name terminal of the primary auxiliary winding of the main transformer, and the cathode of the seventh capacitor is connected to the output terminal of the power supply circuit of the PWM generator through the eleventh resistor. The twelfth resistor and the seventh capacitor are connected in series and then connected in parallel with the seventh diode. The positive terminal of the second electrolytic capacitor is connected to the cathode of the seventh diode, and the negative terminal of the second electrolytic capacitor is connected to the negative terminal of the DC input terminal and the opposite-name terminal of the primary auxiliary winding of the main transformer.

[0016] The control circuit of this utility model for a switching power supply can prevent the switching transistor from periodically turning on and off under output short circuit or overload conditions, thereby improving the reliability of the switching power supply protection. [Brief Description of the Drawings]

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a structural block diagram of the switching power supply control circuit according to an embodiment of the present invention.

[0019] Figure 2 This is the main circuit of the switching power supply in an embodiment of this utility model.

[0020] Figure 3 This is the control circuit of this utility model embodiment. [Detailed Implementation]

[0021] The structural framework of the switching power supply control circuit in this embodiment of the utility model is as follows: Figure 1 As shown, it includes a main circuit and a control circuit. The main circuit includes a DC input terminal 11, a power conversion module 12, a transformer 13 (main transformer T2), and a DC output terminal 14; the control circuit includes an external power supply 21, a first control circuit 22, a second control circuit 23, and a PWM generator 24.

[0022] Figure 2 This is a circuit diagram of the main circuit of the switching power supply circuit in an embodiment of the present invention;

[0023] Reference Figure 2 In this embodiment of the invention, the switching power supply topology is a two-transistor forward converter circuit, including:

[0024] DC input terminal 11 includes the bus positive terminal BUS+ and the bus negative terminal GND;

[0025] The power conversion module 12 includes a primary-side circuit, a push-pull drive circuit, and a PWM generator power supply circuit;

[0026] Transformer 13 (main transformer T2) includes a primary winding, a secondary winding, and a primary auxiliary winding;

[0027] DC output terminal 14 includes a positive terminal PV+ and a negative terminal PGND;

[0028] The primary winding is connected to the primary circuit; the primary circuit is connected to the push-pull drive circuit; the secondary winding is connected to the secondary output circuit; the primary auxiliary winding is connected to the power supply circuit of the PWM generator 24.

[0029] The primary circuit includes MOSFETs M1 and M2, resistors R3-R12, current-limiting resistor RB, capacitors C2-C6, electrolytic capacitor E1, Zener diodes Z1 and Z2, and diodes D3-D6. The source of MOSFET M1 is connected to the cathode of clamped diode D6 and the corresponding terminal (pin 1) of the primary winding of transformer 13. The drain of MOSFET M1 is connected to the positive terminal BUS+ of the DC input terminal 11 and the first terminal of capacitor C6. The anode of diode D6 is connected to the negative terminal GND of the bus. The cathode of clamped diode D5 is connected to the MOSFET M1. The drain and anode are connected to the drain of MOSFET M2; the drain of MOSFET M2 is connected to the opposite terminal (pin 4) of the primary winding, and the source is connected to the second terminal of capacitor C6, and is connected to the negative bus GND of DC input terminal 11 through sampling resistor R7. Capacitor C4 is connected in parallel across resistor R7; resistor RB consists of multiple resistors connected in series, with one end of resistor RB connected to the positive bus BUS+ and the other end connected to VCC+, where VCC+ is the control level; the two ends of capacitor C5, electrolytic capacitor E1, and resistor R8 are connected in parallel between the positive bus BUS+ and the negative bus GND.

[0030] The push-pull drive circuit includes resistors R1 and R2, NPN transistor Q1, PNP transistor Q2, diodes D1 and D2, capacitor C1, and push-pull transformer T1. The first end of resistor R1 is connected to the PWM signal output pin OUT of PWM generator 24, and the second end of resistor R1 is connected to the bases of transistors Q1 and Q2. The collector of transistor Q1 and the cathode of diode D1 are connected to the control level VCC+. The emitter of transistor Q1 is connected to the emitter of transistor Q2, the anode of diode D1, and the cathode of diode D2. The collector of transistor Q2 is connected to the anode of diode D2 and the negative terminal GND of the bus. The emitter of transistor Q1 is connected to the same-name terminal of the primary winding of push-pull transformer T1 via resistor R2 and capacitor C1, and the collector of transistor Q2 is connected to the opposite-name terminal of the primary winding of push-pull transformer T1.

[0031] The push-pull transformer T1 includes two secondary windings. The gate of MOSFET M1 is connected to the same-name terminal of the first secondary winding of push-pull transformer T1 via resistor R4 and capacitor C2. The source of MOSFET M1 is connected to the opposite-name terminal of the first secondary winding of push-pull transformer T1. The cathode of Zener diode Z1 is connected to the gate of MOSFET M1, and the anode of Zener diode Z1 is connected to the source of MOSFET M1. Resistor R9 is connected in parallel with Zener diode Z1. The anode of diode D3 is connected to the gate of MOSFET M1, and the cathode of diode D3 is connected to the first terminal of resistor R3. The second terminal of resistor R3 is connected to resistor R4 and capacitor C2. The connection point of capacitor C2; the gate of MOSFET M2 is connected to the same-name terminal of the second secondary winding of push-pull transformer T1 through resistor R6 and capacitor C3 in sequence, and the source of MOSFET M2 is connected to the opposite-name terminal of the first secondary winding of push-pull transformer T1; the cathode of Zener diode Z2 is connected to the gate of MOSFET M2, the anode of Zener diode Z2 is connected to the source of MOSFET M2, and resistor R10 is connected in parallel with Zener diode Z2; the anode of diode D4 is connected to the gate of MOSFET M2, the cathode of diode D4 is connected to the first terminal of resistor R5, and the second terminal of resistor R5 is connected to the connection point of resistor R6 and capacitor C3;

[0032] The secondary output circuit of transformer 13 includes an output rectifier diode D8, a freewheeling diode D9, an output filter electrolytic capacitor E3, an energy storage inductor L1, resistors R13 and R14, capacitors C8 and C9, and a load resistor RL. The anode of the output diode D8 is connected to the same-name terminal (pins 9-12) of the secondary winding of transformer 13, and the opposite-name terminal (pins 13-16) of the secondary winding of transformer 13 is connected to the ground PGND of the DC output terminal. The cathode of the output diode D8 is connected to the positive terminal PV+ of the DC output terminal through the energy storage inductor L1. The positive terminal of the output filter capacitor E3 and the first terminal of the load resistor RL are connected to the positive terminal PV+ of the DC output terminal 14. The anode of the freewheeling diode D9, the negative terminal of the output filter capacitor E3, and the second terminal of the load resistor RL are connected to the ground PGND of the DC output terminal 14. The cathode of the freewheeling diode D9 is connected to the cathode of the output diode D8. Resistor R13 and capacitor C8 are connected in series and then in parallel with diode D8. Resistor R14 and capacitor C9 are connected in series and then in parallel with diode D9.

[0033] The PWM generator power supply circuit for transformer 13 (main transformer T2) includes resistors R11 and R12, capacitor C7, diode D7, and electrolytic capacitor E2. The anode of capacitor C7 is connected to the same-name terminal of the primary auxiliary winding of main transformer T2, and the cathode of capacitor C7 is connected to the output terminal of the PWM generator power supply circuit through resistor R11. Resistor R12 and capacitor C7 are connected in series and then in parallel with diode D7. The positive terminal of electrolytic capacitor E2 is connected to the cathode of diode D7, and the negative terminal of electrolytic capacitor E2 is connected to the negative terminal of the DC input and the opposite-name terminal of the primary auxiliary winding of main transformer T2. After the circuit starts operating, the PWM generator power supply circuit charges electrolytic capacitor E2. When the power supply is operating in the positive half-cycle, the bus voltage directly supplies power to the primary auxiliary winding of main transformer T2 at the control level VCC+ through MOSFET M1, pins 1 and 4 of the primary winding of main transformer T2, and MOSFET M2, thereby powering the PWM generator 24.

[0034] Figure 3 This is a circuit diagram of the control circuit in an embodiment of the present invention;

[0035] Reference Figure 3 The first control circuit in this embodiment of the present invention includes resistors R15 to R19, capacitors C10 and C11, electrolytic capacitor E4, Zener diode Z3 and Z4, optocoupler U1 and optocoupler U2.

[0036] The voltage at the DC output terminal PV+ of the main circuit is divided by resistors R15 and R16 and then connected to the cathode of Zener diode Z3. The anode of Zener diode Z3 is connected to the anode (pin 1) of the LED of optocoupler U1. The cathode (pin 2) of the LED is grounded to PGND. The emitter (pin 3) of the phototransistor of optocoupler U1 is connected to the negative terminal of electrolytic capacitor E4, and the collector (pin 4) is connected to the positive terminal of electrolytic capacitor E4 and the positive terminal of input terminal J1 of external power supply 21. The first end of resistor R18 is connected to the negative terminal of electrolytic capacitor E4, and the second end of resistor R18 is connected to the cathode of Zener diode Z4 through resistor R19. The anode of Zener diode Z4 is connected to the negative terminal of input terminal J1 of external power supply 21. The anode (pin 1) of the LED of optocoupler U2 is connected to the second end of resistor R18, and the cathode (pin 2) is connected to the cathode of Zener diode Z4. Resistor R17 and capacitor C10 are connected in parallel between the positive and negative terminals of external power supply 21, and capacitor C11 is connected in parallel with resistor R19.

[0037] The collector (pin 4) of the phototransistor U2 is connected to the control level VCC+, and the emitter (pin 3) of the phototransistor U2 is connected to the switch level ON / OFF.

[0038] Reference Figure 3The second control circuit in this embodiment of the present invention includes a PWM generator U3 (including a switching power supply control chip UC2844), resistors R20 to R23, a thermistor NTC, capacitors C12 and C13, an electrolytic capacitor E5, a PMOS transistor Q3, and an NPN transistor Q4.

[0039] The collector of NPN transistor Q4 is connected to the gate of PMOS transistor Q3 through resistor R20, and connected to the control level VCC+ through resistor R21.

[0040] The ON / OFF switch level is divided by resistors R22 and R23 and then connected to the base of NPN transistor Q4. Capacitor C13 is connected in parallel across resistor R22.

[0041] The emitter of NPN transistor Q4 is connected to the negative terminal of the bus, GND.

[0042] The source of PMOS transistor Q3 is connected to the control level VCC+ through the thermistor NTC, and at the same time connected to the negative terminal GND of the bus through the electrolytic capacitor E5.

[0043] The drain of PMOS transistor Q3 is connected to the power supply pin VCC of PWM generator U3, and is also connected to the negative terminal GND of the bus through capacitor C12.

[0044] When the switch level ON / OFF turns high, the Vce of transistor Q4 is turned on and at a low level. At this time, the Vgs of PMOS transistor Q3 is low, controlling Vsd to turn on and at a high level, supplying power to the PWM generator. The thermistor NTC suppresses the power-on inrush current. When the switch level ON / OFF turns low, the Vce of transistor Q4 is not turned on, controlling the Vgs of MOS transistor Q3 to be low, Vsd is not turned on, and the PWM generator is turned off.

[0045] The working principle of the switching power supply control circuit of this utility model is as follows:

[0046] 1) In the first control circuit, when the external power input terminal J1 is connected to the voltage, it charges the electrolytic capacitor E4. Utilizing the charging and discharging characteristics of the electrolytic capacitor E4, power is supplied to pins 1-2 of the optocoupler U2 through resistor R18. Pins 3-4 of the optocoupler U2 are turned on, making the control level VCC+ and the switch level pin ON / OFF in the second control circuit conduct. The switch level pin ON / OFF turns to a high level. It also continuously supplies power to the power supply pin (pin 7 VCC) of the PWM generator U3. The PWM generator starts working, and the PWM signal is output to the power conversion module 12 of the main circuit, which is the output voltage of the main circuit of the switching power supply.

[0047] 2) When the main circuit of the switching power supply outputs a normal voltage, the DC output terminal PV+ is divided by resistors R15 and R16 and then supplied to pins 1 and 2 of optocoupler U1 through Zener diode Z3, thus establishing a closed-loop system.

[0048] 3) When the main circuit of the switching power supply experiences an output short circuit, the DC input terminal PV+ of the main circuit of the switching power supply has no output voltage, the level of pins 1-2 of optocoupler U1 is lower than the conduction threshold level of the optocoupler, and pins 3-4 of optocoupler U1 are not conducting. At this time, the external power input terminal J1 no longer supplies power to pins 1-2 of optocoupler U2, pins 3-4 of optocoupler U2 are not conducting, the ON / OFF level pin of the switching level turns to a low level, the PWM generator turns off the PWM waveform level output by the OUT pin, and the main circuit of the switching power supply stops working and will not self-oscillate or repeatedly start.

[0049] The control circuit of this utility model of the switching power supply can prevent the switching transistor from periodically turning on and off under output short circuit or overload conditions, thereby improving the reliability of the switching power supply protection and preventing damage caused by repeated starts due to long short circuit cycles.

Claims

1. A control circuit for a switching power supply, comprising a PWM generator, the switching power supply comprising a main circuit, the main circuit comprising a DC input terminal, a power conversion module, and a DC output terminal, the PWM signal output terminal of the PWM generator being connected to the PWM signal input terminal of the power conversion module; characterized in that, The system includes a first control circuit and a second control circuit. The first control circuit includes a switch signal generation circuit and a closed-loop monitoring and short-circuit protection circuit. The second control circuit includes a PWM generator power supply control circuit. The input terminal of the PWM generator power supply control circuit is connected to the PWM generator power supply, and the output terminal is connected to the power input terminal of the PWM generator. The control terminal of the PWM generator power supply control circuit is connected to the switch signal output terminal of the switch signal generation circuit, and the input terminal of the switch signal generation circuit is connected to an external DC power supply. The input terminal of the closed-loop monitoring and short-circuit protection circuit is connected to the DC output terminal of the main circuit, and the output terminal is connected to the control terminal of the switch signal generation circuit.

2. The control circuit of the switching power supply according to claim 1, characterized in that, The switching signal generation circuit includes a second optocoupler, a first voltage divider circuit, and a fourth electrolytic capacitor. The positive terminal of the fourth electrolytic capacitor is connected to the positive terminal of an external DC power supply, the negative terminal of the fourth electrolytic capacitor is connected to the first terminal of the first voltage divider circuit, and the second terminal of the first voltage divider circuit is connected to the negative terminal of the external DC power supply. The anode of the second optocoupler's LED is connected to the voltage signal output terminal of the first voltage divider circuit, and the cathode is connected to the second terminal of the first voltage divider circuit. The collector of the second optocoupler's phototransistor is connected to the control level, and the emitter is connected to the switching signal output terminal of the switching signal generation circuit. The closed-loop monitoring and short-circuit protection circuit includes a second voltage divider circuit and a first optocoupler. The second voltage divider circuit is connected between the positive and negative terminals of the DC output terminal. The voltage signal output terminal of the second voltage divider circuit is connected to the anode of the first optocoupler's LED, and the cathode of the first optocoupler's LED is connected to the negative terminal of the DC output terminal. The collector of the first optocoupler's phototransistor is connected to the positive terminal of the fourth electrolytic capacitor, and the emitter is connected to the negative terminal of the fourth electrolytic capacitor.

3. The control circuit of the switching power supply according to claim 2, characterized in that, The closed-loop monitoring and short-circuit protection circuit includes a third Zener diode, the anode of which is connected to the anode of the first optocoupler LED, and the cathode of which is connected to the voltage signal output terminal of the second voltage divider circuit. The switching signal generation circuit includes a fourth Zener diode, a tenth capacitor, a seventeenth resistor, and an eleventh capacitor. The anode of the fourth Zener diode is connected to the negative terminal of the external DC power supply, and the cathode is connected to the cathode of the second optocoupler LED. The fourth Zener diode and the tenth capacitor are connected in parallel with the external DC power supply, and the eleventh capacitor is connected in parallel with the cathode of the second optocoupler LED.

4. The control circuit of the switching power supply according to claim 2, characterized in that, The PWM generator power supply control circuit includes a fourth NPN transistor, a PMOS transistor, a twentieth resistor, and a twenty-first resistor. The source of the PMOS transistor is connected to the positive terminal of the PWM generator power supply, and the power input terminal of the PWM generator is connected to the drain of the PMOS transistor. The collector of the fourth NPN transistor is connected to the power input terminal of the PWM generator through the twenty-first resistor, and to the gate of the PMOS transistor through the twentieth resistor. The base of the fourth NPN transistor is connected to the switch signal output terminal of the switch signal generation circuit, and the emitter is connected to the negative terminal of the DC input terminal.

5. The control circuit of the switching power supply according to claim 4, characterized in that, The PWM generator power supply control circuit includes a thermistor, a twelfth capacitor, a thirteenth capacitor, a fifth electrolytic capacitor, a twenty-second resistor, and a twenty-third resistor. The source of the PMOS transistor is connected to the positive terminal of the PWM generator power supply through the thermistor and to the negative terminal of the DC input through the fifth electrolytic capacitor. The base of the fourth NPN transistor is connected to the switch signal output terminal of the switch signal generation circuit through the twenty-third resistor and to the negative terminal of the DC input through the twenty-second resistor. The thirteenth capacitor and the twenty-second resistor are connected in parallel. The drain of the PMOS transistor is connected to the negative terminal of the DC input through the twelfth capacitor.

6. The control circuit of the switching power supply according to claim 1, characterized in that, The main circuit includes a main transformer and a secondary output circuit of the main transformer. The power conversion module includes a primary circuit of the main transformer, a push-pull drive circuit, and a PWM generator power supply circuit. The primary circuit of the main transformer is connected to the primary winding of the main transformer, the secondary output circuit of the main transformer is connected to the secondary winding of the main transformer, and the power supply circuit of the PWM generator is connected to the primary auxiliary winding of the main transformer. The output terminal of the power supply circuit of the PWM generator is the power supply for the PWM generator.

7. The control circuit of the switching power supply according to claim 6, characterized in that, The primary circuit of the main transformer includes a first MOSFET, a second MOSFET, a sampling resistor, a first clamping diode, a second clamping diode, a first Zener diode, and a second Zener diode. The source of the first MOSFET and the cathode of the first clamping diode are connected to the same-name terminals of the primary winding of the main transformer. The drain of the first MOSFET is connected to the positive terminal of the DC input and the first terminal of the sixth capacitor. The anode of the first clamping diode is connected to the negative terminal of the DC input. The cathode of the second clamping diode is connected to the drain of the first MOSFET, and the anode is connected to the drain of the second MOSFET. The drain of the second MOSFET is connected to the opposite-name terminal of the primary winding. The source of the second MOSFET is connected to the second terminal of the sixth capacitor and connected to the negative terminal of the DC input through the sampling resistor. A fourth capacitor is connected in parallel across the sampling resistor. The DC input includes a current-limiting resistor and a first electrolytic capacitor. The first terminal of the current-limiting resistor is connected to the positive terminal of the DC input and the first terminal is connected to the output terminal of the control level. A fifth capacitor, the first electrolytic capacitor, and an eighth resistor are connected in parallel between the positive and negative terminals of the DC input.

8. The control circuit of the switching power supply according to claim 7, characterized in that, The push-pull drive circuit includes a first resistor, a second resistor, a first NPN transistor, a PNP transistor, a first diode, a second diode, a first capacitor, and a push-pull transformer. The first end of the first resistor is connected to the PWM signal output terminal of the PWM generator, and the second end of the first resistor is connected to the bases of the first NPN transistor and the PNP transistor, respectively. The collector of the first NPN transistor and the cathode of the first diode are connected to the output terminal of the control level, respectively. The emitter of the first NPN transistor is connected to the emitter of the PNP transistor, the anode of the first diode, and the cathode of the second diode, respectively, and is connected to the same-name terminal of the primary winding of the push-pull transformer via the second resistor and the first capacitor connected in series. The collector of the PNP transistor is connected to the anode of the second diode and the negative terminal of the DC input terminal, and is connected to the opposite-name terminal of the primary winding of the push-pull transformer. The push-pull transformer includes two secondary windings. The gate of the first MOSFET is connected to the same-name terminal of the first secondary winding of the push-pull transformer via a fourth resistor and a second capacitor. The source of the first MOSFET is connected to the opposite terminal of the first secondary winding of the push-pull transformer; the cathode of the first Zener diode is connected to the gate of the first MOSFET, and the anode of the first Zener diode is connected to the source of the first MOSFET; the ninth resistor is connected in parallel with the first Zener diode; the anode of the third diode is connected to the gate of the first MOSFET, and the cathode of the third diode is connected to the first terminal of the third resistor; the second terminal of the third resistor is connected to the connection point of the fourth resistor and the second capacitor; the gate of the second MOSFET is connected to the same terminal of the second secondary winding of the push-pull transformer through the sixth resistor and the third capacitor in sequence, and the source of the second MOSFET is connected to the opposite terminal of the first secondary winding of the push-pull transformer; the cathode of the second Zener diode is connected to the gate of the second MOSFET, and the anode of the second Zener diode is connected to the source of the second MOSFET; the tenth resistor is connected in parallel with the second Zener diode; the anode of the fourth diode is connected to the gate of the second MOSFET, and the cathode of the fourth diode is connected to the first terminal of the fifth resistor; the second terminal of the fifth resistor is connected to the connection point of the sixth resistor and the third capacitor.

9. The control circuit of the switching power supply according to claim 6, characterized in that, The secondary output circuit of the main transformer includes an output rectifier diode, a freewheeling diode, an output filter electrolytic capacitor, an energy storage inductor, a thirteenth resistor, a fourteenth resistor, an eighth capacitor, a ninth capacitor, and a load resistor. The anode of the output rectifier diode is connected to the same-name terminal of the secondary winding of the main transformer, and the opposite-name terminal of the secondary winding of the main transformer is connected to the negative terminal of the DC output terminal. The cathode of the output rectifier diode is connected to the positive terminal of the DC output terminal through the energy storage inductor. The positive terminal of the output filter electrolytic capacitor and the first terminal of the load resistor are connected to the positive terminal of the DC output terminal. The anode of the freewheeling diode, the negative terminal of the output filter electrolytic capacitor, and the second terminal of the load resistor are connected to the negative terminal of the DC output terminal. The cathode of the freewheeling diode is connected to the cathode of the output rectifier diode. The thirteenth resistor and the eighth capacitor are connected in series and then in parallel with the output rectifier diode. The fourteenth resistor and the ninth capacitor are connected in series and then in parallel with the freewheeling diode.

10. The control circuit of the switching power supply according to claim 6, characterized in that, The power supply circuit for the PWM generator includes an eleventh resistor, a twelfth resistor, a seventh capacitor, a seventh diode, and a second electrolytic capacitor. The anode of the seventh capacitor is connected to the same-name terminal of the primary auxiliary winding of the main transformer, and the cathode of the seventh capacitor is connected to the output terminal of the power supply circuit of the PWM generator through the eleventh resistor. The twelfth resistor and the seventh capacitor are connected in series and then connected in parallel with the seventh diode. The positive terminal of the second electrolytic capacitor is connected to the cathode of the seventh diode, and the negative terminal of the second electrolytic capacitor is connected to the negative terminal of the DC input terminal and the opposite-name terminal of the primary auxiliary winding of the main transformer.

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