A short circuit protection circuit for a forward type switching power supply of servo drive

Abstract

The utility model discloses a kind of for servo drive's forward-type switching power supply short-circuit protection circuit, including PWM controller, power switch tube and short-circuit protection circuit, short-circuit protection circuit includes opto-isolator isolation component and switch drive circuit;The input end of opto-isolator isolation component is connected to power short-circuit signal, for when receiving power short-circuit signal, disconnect opto-coupler passage;The output end of opto-isolator isolation component is connected to PWM controller by switch drive circuit, to make PWM controller stop working by the off state of opto-isolator isolation component when power short-circuit.This scheme uses opto-coupler U44 to replace capacitor element and realizes self-starting, the protection circuit provided can realize short-circuit protection and self-starting when short-circuit recovery, while, frequent restart problem can also be effectively avoided, overcome the power device and transformer heating problem caused by frequent restart.

Description

Technical Field

[0001] This utility model belongs to the field of switching power supply technology, and in particular relates to a short-circuit protection circuit for a forward switching power supply used in servo drive. Background Technology

[0002] A forward converter is a common DC-DC or AC-DC power supply topology. Its core feature is that when the switching transistor is turned on, the input voltage transfers energy directly to the secondary side through the primary winding of the transformer. The secondary rectifier diode is turned on, supplying power to the load and charging the energy storage inductor. When the switching transistor is turned off, the secondary rectifier diode is turned off, and the energy storage inductor releases energy through the freewheeling diode, maintaining the continuity of the load current.

[0003] Typical forward converter switching power supplies are designed with short-circuit protection circuits. To achieve self-starting, these protection circuits also include energy storage capacitors. When a short circuit occurs at the output, the current increases sharply. The protection circuit triggers the switching transistor to turn off, stopping energy output. Simultaneously, the protection circuit slowly discharges the accumulated energy. As the energy is discharged, the voltage at the critical node in the protection circuit gradually rises. When the voltage rises to a certain threshold, the circuit attempts to turn the switching transistor back on to restore energy output. If the short circuit is not resolved at this point, the output current will surge again, and the protection circuit will immediately trigger shutdown again, repeating the "discharge-recovery-restart-shutdown" cycle. This creates a frequent "start-shutdown" switching mode. Prolonged exposure to this frequent switching mode can cause the power devices and transformer to overheat, potentially leading to damage. Utility Model Content

[0004] The purpose of this invention is to address the above-mentioned problems by providing a short-circuit protection circuit for a forward switching power supply used in servo drives. This circuit provides short-circuit protection for the switching power supply without frequent restarts, thus preventing overheating of power devices and transformers.

[0005] A short-circuit protection circuit for a forward switching power supply used in servo drive includes a PWM controller, a power switching transistor, and a short-circuit protection circuit, wherein the short-circuit protection circuit includes an optocoupler isolation component and a switching drive circuit. The input terminal of the optocoupler isolation component is connected to a power short-circuit signal, which is used to disconnect the optocoupler path when a power short-circuit signal is received. The output terminal of the optocoupler isolation component is connected to the PWM controller through the switch driving circuit, so that the PWM controller stops working when the power supply is short-circuited by the off state of the optocoupler isolation component.

[0006] In the aforementioned short-circuit protection circuit for a forward switching power supply used for servo drive, the optocoupler isolation component is an optocoupler U44. The input side of the optocoupler U44 is connected to the power short-circuit signal, and the output side is connected to the switch drive circuit, so that when the power short-circuit signal is received, the PWM controller is stopped by the switch drive circuit.

[0007] In the aforementioned forward switching power supply short-circuit protection circuit for servo drive, the anode pin of the input side of optocoupler U44 is connected to the power supply short-circuit signal, and the cathode pin is connected to analog ground. The emitter pin on the output side of optocoupler U44 is connected to the IPM ground, and the collector pin is connected to the input of the switch drive circuit.

[0008] In the above-mentioned forward switching power supply short-circuit protection circuit for servo drive, the power short-circuit signal is the DC power input. When the power supply is normal, the DC power input is normal and the optocoupler path is open. When the power supply is short-circuited, the DC input of the power supply is close to zero, and the optocoupler path is disconnected.

[0009] In the aforementioned forward switching power supply short-circuit protection circuit for servo drive, the switching drive circuit includes a PNP transistor QA4, an NPN transistor QA5, and a PNP transistor QA6 connected in sequence. The base of the PNP transistor QA4 is connected to the collector pin of the optocoupler U44, the collector of the PNP transistor QA4 is connected to the base of the NPN transistor QA5, and the emitter is connected to the reference voltage. The collector of the NPN transistor QA5 is connected to the base of the PNP transistor QA6, and the emitter is connected to the IPM ground. The collector of the PNP transistor QA6 is connected to the power supply terminal of the PWM controller, and the emitter is connected to the auxiliary power supply.

[0010] In the above-mentioned short-circuit protection circuit for a forward switching power supply used for servo drive, a current-limiting resistor RA10 is connected in series between the base of the PNP transistor QA4 and the collector on the output side of the optocoupler U44. A current-limiting resistor RA11 is connected in series between the base of the NPN transistor QA5 and the collector of the PNP transistor QA4. A current-limiting resistor RA12 is connected in series between the base of the PNP transistor QA6 and the collector of the NPN transistor QA5.

[0011] In the aforementioned short-circuit protection circuit for a forward switching power supply used for servo drive, a freewheeling diode DA2 is connected in series between the collector of the PNP transistor QA6 and the PWM controller.

[0012] In the aforementioned short-circuit protection circuit for a forward switching power supply used for servo drive, the output terminal of the PWM controller is connected to the power switching transistor, the power supply terminal is connected to the collector of the PNP transistor QA6, the RT / CT terminal is connected to the collector of the PNP transistor QA4 through resistor R262, and is connected to the IPM ground terminal GND_IPM through capacitor C228.

[0013] In the aforementioned short-circuit protection circuit for a forward switching power supply used for servo drive, the voltage feedback terminal of the PWM controller is connected to a voltage feedback loop, and the voltage feedback loop includes a reference voltage source U41 and a second optocoupler U40.

[0014] In the aforementioned short-circuit protection circuit for a forward switching power supply used for servo drive, the power switching transistor is an N-channel enhancement-mode MOSFET, with its gate connected to the output terminal of the PWM controller, its source connected to the IPM ground terminal, and its drain connected to the primary winding of the transformer.

[0015] The advantages of this utility model are: this solution uses optocoupler U44 to replace capacitor components to achieve self-starting. The protection circuit provided can achieve short circuit protection and self-starting when the short circuit is restored, while also effectively avoiding the problem of frequent restarts and overcoming the problem of power devices and transformer overheating caused by frequent restarts. Attached Figure Description

[0016] Figure 1 This is a structural block diagram of the short-circuit protection circuit for a forward switching power supply used in servo drives according to this utility model. Figure 2 This is a circuit diagram of the short-circuit protection circuit for a forward switching power supply used in servo drives according to this utility model. Figure 3 yes Figure 2 The original circuit diagram of the short-circuit protection circuit section is shown in the image.

[0017] Figure label: PWM controller 1; power switching transistor 2; short circuit protection circuit 3; transformer 4. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1 and Figure 2 As shown, this embodiment discloses a short-circuit protection circuit for a forward switching power supply used in servo drive, which has a DC input of +24V and includes a PWM controller 1, a power switching transistor 2, a short-circuit protection circuit 3, a transformer, etc.

[0020] Among them, such as Figure 2 and Figure 3As shown, the short-circuit protection circuit 3 includes an optocoupler isolation component and a switch drive circuit.

[0021] The optocoupler isolation component is an optocoupler U44. The input side of the optocoupler U44 is connected to the power supply short-circuit signal to disconnect the optocoupler path when the power supply short-circuit signal is received. The output side is connected to the PWM controller 1 through a switch drive circuit so that the PWM controller 1 can be stopped when the power supply short-circuit signal is received.

[0022] Specifically, the power supply short-circuit signal is the +24V DC power input. The anode pin of the optocoupler U44 input side is connected to the +24V DC power input, and the cathode pin is connected to analog ground AGND. The emitter pin of the optocoupler U44 output side is connected to the IPM ground GND_IPM, and the collector pin is connected to the input of the switch driver circuit. When the power supply is normal, the +24V DC power input is normal, and the optocoupler path is on; when the power supply is short-circuited, the +24V DC power input is close to zero, and the optocoupler path is disconnected.

[0023] The switch drive circuit includes a PNP transistor QA4, an NPN transistor QA5, and a PNP transistor QA6 connected in sequence.

[0024] The base of PNP transistor QA4 is connected to the collector pin of optocoupler U44 through current-limiting resistor RA10. The collector of PNP transistor QA4 is connected to the base of NPN transistor QA5 through current-limiting resistor RA11. The emitter is connected to the reference voltage VREF1.

[0025] The collector of NPN transistor QA5 is connected to the base of PNP transistor QA6 through current-limiting resistor RA12, and the emitter is connected to the IPM ground terminal GND_IPM.

[0026] The collector of PNP transistor QA6 is connected to the power supply terminal of PWM controller 1 via freewheeling diode DA2, and the emitter is connected to the auxiliary power supply +15V_IPM. Freewheeling diode DA2 is used to prevent reverse voltage at the gate of power switch 2 from damaging the drive circuit.

[0027] Specifically, the PWM controller 1 includes a PWM control chip U10. Its output pin 6 (Out) is connected to the power switch 2, its power supply pin 7 (Vcc) is connected to the collector of the PNP transistor QA6, and its pin 4 (RT / CT) is connected to the collector of the PNP transistor QA4 through resistor R262, and to the IPM ground GND_IPM through capacitor C228. When the optocoupler U44 is on, PNP transistors QA4, NPN transistors QA5, and PNP transistor QA6 conduct sequentially, Va+ approaches the auxiliary power supply 15V_IPM, and the U10 chip operates. When the optocoupler U44 is off, PNP transistors QA4, NPN transistors QA5, and PNP transistor QA6 are all off, Va+ has no voltage, and the U10 chip stops operating.

[0028] Furthermore, the voltage feedback terminal 2 (Vfb) of the U10 chip is connected to the voltage feedback loop, and the voltage feedback loop includes a reference voltage source U41 and a second optocoupler U40.

[0029] like Figure 2 As shown, the reference terminal of the reference voltage source U41 is connected to the DC power input through a rectifier and filter circuit, the cathode is connected to the cathode pin on the input side of the second optocoupler U40, and the anode is connected to analog ground AGND.

[0030] The anode pin on the input side of the second optocoupler U40 is connected to the DC power input of +24V, and the collector pin 4 on the output side is connected to the voltage feedback terminal of the PWM controller 1, which is used to isolate and transmit the DC power input signal to the PWM controller 1.

[0031] Furthermore, the power switch 2 is an N-channel enhancement-mode MOSFET, with its gate connected to the output terminal of the PWM controller 1, its source connected to the IPM ground terminal GND_IPM, and its drain connected to the primary winding of the transformer 4.

[0032] The circuit works as follows: When the +24V power supply is short-circuited, optocoupler U44 disconnects, QA4 turns off, and QA5 and QA6 also turn off, preventing pin 4 of U10 from oscillating. Simultaneously, the voltage across Va+ drops, causing U10 to stop working, thus protecting the circuit. The circuit then waits for the power supply to be restored, without attempting to reconnect. Until the +24V power supply returns to normal, optocoupler U44 remains off, preventing U10 from restarting and thus preventing the MOSFET and transformer from overheating. Once the +24V power supply returns to normal, optocoupler U44 turns on, the Va+ voltage rises, U10 restarts, and pin 4 begins to oscillate.

[0033] The specific embodiments described herein are merely illustrative examples illustrating the spirit of this utility model. Those skilled in the art to which this utility model pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this utility model or exceeding the scope defined by the appended claims.

[0034] Although this document frequently uses terms such as PWM controller 1, power switching transistor 2, short-circuit protection circuit 3, and transformer 4, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention.

Claims

1. A short-circuit protection circuit for a forward switching power supply used in servo drives, comprising a PWM controller (1), a power switching transistor (2), and a short-circuit protection circuit (3), characterized in that, The short-circuit protection circuit (3) includes an optocoupler isolation component and a switch drive circuit; The input terminal of the optocoupler isolation component is connected to a power short-circuit signal, which is used to disconnect the optocoupler path when a power short-circuit signal is received. The output terminal of the optocoupler isolation component is connected to the PWM controller (1) through the switch driving circuit so that the PWM controller (1) stops working when the power supply is short-circuited by the off state of the optocoupler isolation component.

2. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 1, characterized in that, The aforementioned optocoupler isolation component is an optocoupler U44; The input side of the optocoupler U44 is connected to the power supply short-circuit signal, and the output side is connected to the switch drive circuit, so that when the power supply short-circuit signal is received, the PWM controller (1) is stopped by the switch drive circuit.

3. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 2, characterized in that, The anode pin on the input side of optocoupler U44 is connected to the power supply short-circuit signal, and the cathode pin is connected to analog ground; The emitter pin on the output side of optocoupler U44 is connected to the IPM ground, and the collector pin is connected to the input of the switch drive circuit.

4. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 3, characterized in that, The power short-circuit signal is the DC power input. When the power supply is normal, the DC power input is normal and the optocoupler path is open. When the power supply is short-circuited, the DC input of the power supply is close to zero, and the optocoupler path is disconnected.

5. The short-circuit protection circuit for a forward switching power supply for servo drive according to any one of claims 2 to 4, characterized in that, The switch drive circuit includes a PNP transistor QA4, an NPN transistor QA5, and a PNP transistor QA6 connected in sequence. The base of the PNP transistor QA4 is connected to the collector pin of the optocoupler U44, the collector of the PNP transistor QA4 is connected to the base of the NPN transistor QA5, and the emitter is connected to the reference voltage. The collector of the NPN transistor QA5 is connected to the base of the PNP transistor QA6, and the emitter is connected to the IPM ground. The collector of the PNP transistor QA6 is connected to the power supply terminal of the PWM controller (1), and the emitter is connected to the auxiliary power supply.

6. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 5, characterized in that, A current-limiting resistor RA10 is connected in series between the base of the PNP transistor QA4 and the collector on the output side of the optocoupler U44. A current-limiting resistor RA11 is connected in series between the base of the NPN transistor QA5 and the collector of the PNP transistor QA4. A current-limiting resistor RA12 is connected in series between the base of the PNP transistor QA6 and the collector of the NPN transistor QA5.

7. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 5, characterized in that, A freewheeling diode DA2 is connected in series between the collector of the PNP transistor QA6 and the PWM controller (1).

8. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 5, characterized in that, The output terminal of the PWM controller (1) is connected to the power switching transistor (2), the power supply terminal is connected to the collector of the PNP transistor QA6, the RT / CT terminal is connected to the collector of the PNP transistor QA4 through resistor R262, and is connected to the IPM ground terminal GND_IPM through capacitor C228.

9. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 8, characterized in that, The voltage feedback terminal of the PWM controller (1) is connected to the voltage feedback loop, and the voltage feedback loop includes a reference voltage source U41 and a second optocoupler U40.

10. The short-circuit protection circuit for a forward switching power supply for servo drive according to claim 1, characterized in that, The power switch (2) is an N-channel enhancement-mode MOS transistor, with its gate connected to the output terminal of the PWM controller (1), its source connected to the IPM ground terminal, and its drain connected to the primary winding of the transformer (4).

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