Switching power supply output short circuit protection circuit based on constant current loop and switching power supply

Abstract

The invention discloses a switching power supply output short-circuit protection circuit based on a constant current loop and a switching power supply, the switching power supply output short-circuit protection circuit comprises a sampling circuit, an amplifying circuit, an error amplifying circuit and a feedback control circuit which are connected in sequence, and further comprises a trigger circuit, the output end of the trigger circuit is connected to the first input end of the error amplifying circuit, and the output end of the error amplifying circuit is connected to the second input end of the feedback control circuit. The trigger circuit reduces the reference voltage of the error amplification circuit when the output of the switching power supply is short-circuited, so that the constant current point of the switching power supply is reduced. On the basis of a constant-current control circuit formed by sequentially connecting a sampling circuit, an amplifying circuit, an error amplifying circuit and a feedback control circuit, a trigger circuit is added. When the output of the switching power supply is short-circuited, the trigger circuit can reduce the reference voltage of the error amplifying circuit and further reduce the output constant current point of the switching power supply, so that the stress and loss of a power device are effectively reduced, and the reliability of the power supply is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of switching power supply technology, specifically relating to a switching power supply output short-circuit protection circuit based on a constant current loop and the switching power supply itself. Background Technology

[0002] With the application and development of switching power supply technology, maintaining a constant current state during output short-circuit protection has become a trend, and constant current loop control technology has become a common strategy for solving this problem. Existing constant current loops are... Figure 1 The constant current point of a switching power supply during a short circuit is generally designed to be 1.1 times or more of the normal operating output current. When short-circuiting for a long period of time, the power devices are subjected to higher stress and losses than during normal operation, which puts great pressure on device selection and affects the reliability of the switching power supply. Summary of the Invention

[0003] The purpose of this invention is to provide a switching power supply output short-circuit protection circuit and switching power supply based on a constant current loop, which solves the problem that the power devices are subjected to high stress and loss when the output of the switching power supply is short-circuited in the existing constant current control loop.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a short-circuit protection circuit for the output of a switching power supply based on a constant current loop, comprising a sampling circuit, an amplification circuit, an error amplification circuit, and a feedback control circuit connected in sequence, and further comprising a trigger circuit, wherein the output terminal of the trigger circuit is connected to the first input terminal of the error amplification circuit, and the trigger circuit reduces the reference voltage of the error amplification circuit when the output of the switching power supply is short-circuited, thereby lowering the constant current point of the switching power supply.

[0005] Optionally, the trigger circuit includes a bypass module and a trigger module. The bypass module is connected to the trigger module. The input terminal of the bypass module is connected to the positive output terminal of the switching power supply. The input terminal of the trigger module is connected to an auxiliary source. The output terminal of the trigger module is connected to the first input terminal of the error amplifier circuit.

[0006] Optionally, the bypass module includes a second capacitor, a ninth resistor, a second switching transistor, a third capacitor, a tenth resistor, a first Zener diode, and an eleventh resistor; the first terminal of the second capacitor is connected to the trigger module and the first terminal of the ninth resistor, the second terminal of the ninth resistor is connected to the first terminal of the second switching transistor, the control terminal of the second switching transistor is connected to the first terminal of the third capacitor, the first terminal of the tenth resistor, and the anode of the first Zener diode, the second terminal of the second switching transistor, the second terminal of the second capacitor, the second terminal of the tenth resistor, and the second terminal of the third capacitor are grounded, and the cathode of the first Zener diode is connected to the positive output terminal of the switching power supply through the eleventh resistor.

[0007] Optionally, the trigger module includes a fourteenth resistor, an eighth resistor, a second Zener diode, a first capacitor, a seventh resistor, and a second switching transistor. The first end of the fourteenth resistor is connected to an auxiliary source. The second end of the fourteenth resistor is connected to the first end of the eighth resistor and the bypass module. The second end of the eighth resistor is connected to the cathode of the second Zener diode. The anode of the second Zener diode is connected to the control terminal of the first switching transistor. The first end of the second switching transistor is connected to the first input terminal of the error amplifier circuit through the seventh resistor. The second end of the second switching transistor is grounded. The control terminal of the second switching transistor is grounded through the third capacitor.

[0008] Optionally, the error amplifier circuit includes a second operational amplifier, a thirteenth resistor, a fourth capacitor, a fourth resistor, a fifth resistor, and a sixth resistor. The first terminal of the fourth capacitor is connected to the inverting input terminal of the second operational amplifier, and the second terminal of the fourth capacitor is connected to the output terminal of the second operational amplifier through the thirteenth resistor. The output terminal of the second operational amplifier is connected to the input terminal of the feedback control circuit, and the inverting input terminal of the second operational amplifier is connected to the output terminal of the amplifier circuit through the fourth resistor. The first terminal of the fifth resistor is connected to an auxiliary source, and the second terminal of the fifth resistor is connected to the first terminal of the sixth resistor, the non-inverting input terminal of the second operational amplifier, and the output terminal of the trigger circuit. The second terminal of the sixth resistor is grounded.

[0009] Optionally, the amplification circuit includes a first resistor, a second resistor, a third resistor, and a first operational amplifier; the first end of the third resistor is connected to the output terminal of the first operational amplifier, the second end of the third resistor is connected to the inverting input terminal of the first operational amplifier, the first end of the second resistor is grounded, the second end of the second resistor is connected to the inverting input terminal of the first operational amplifier, the first end of the first resistor is connected to the non-inverting input terminal of the first operational amplifier, the second end of the first resistor is connected to the output terminal of the sampling circuit, and the output terminal of the first operational amplifier is connected to the second input terminal of the error amplifier circuit.

[0010] Optionally, the sampling circuit includes a sampling resistor connected in series in the output circuit of the switching power supply. The first end of the sampling resistor is the current sampling signal point, and the second end of the sampling resistor is grounded.

[0011] Optionally, the feedback control circuit includes a twelfth resistor and an optocoupler; the optocoupler includes a first pin, a second pin, a third pin, and a fourth pin; the first end of the twelfth resistor is connected to an auxiliary source, and the second end of the twelfth resistor is connected to the first pin of the optocoupler; the second pin of the optocoupler is connected to the output terminal of the operational amplifier circuit; the third pin of the optocoupler is connected to the ground terminal of the control IC, and the fourth pin of the optocoupler is connected to the feedback control pin of the control IC.

[0012] In a second aspect, the present invention also provides a switching power supply, including the constant current loop-based switching power supply output short-circuit protection circuit as described in the first aspect.

[0013] The beneficial effects of this invention are as follows: This invention adds a trigger circuit to a constant current control circuit consisting of a sampling circuit, an amplification circuit, an error amplification circuit, and a feedback control circuit connected in sequence. When the switching power supply output is short-circuited, the trigger circuit lowers the reference voltage of the error amplification circuit, thereby lowering the constant current point of the switching power supply output. This effectively reduces the stress and losses of the power devices and greatly improves the reliability of the power supply. Attached Figure Description

[0014] Figure 1 A framework diagram of existing constant current control loop technology provided for embodiments of the present invention. Figure 2 A framework diagram of a switching power supply output short-circuit protection circuit based on a constant current loop is provided for an embodiment of the present invention.

[0015] Figure 3 Partial circuit schematics (including trigger circuit diagrams) provided for embodiments of the present invention.

[0016] Figure 4The circuit schematic diagrams provided for embodiments of the present invention include sampling circuits, amplification circuits, error amplification circuits, trigger circuits, and feedback control circuits.

[0017] The circuit includes: sampling circuit 1 with sampling resistor R-cs; amplifier circuit 2 with first operational amplifier U1A, first resistor R1, second resistor R2, and third resistor R3; error amplifier circuit 3 with second operational amplifier U1B, fourth resistor R4, fourth capacitor C4, thirteenth resistor R13, fifth resistor R5, and sixth resistor R6; trigger circuit 4 with trigger module 4-1 with fourteenth resistor R14, eighth resistor R8, second Zener diode D2, first capacitor C1, first switch Q1, and seventh resistor R7; bypass module 4-2 with second capacitor C2, ninth resistor R9, second switch Q2, tenth resistor R10, third capacitor C3, first Zener diode D1, and eleventh resistor R11; and feedback control circuit 5 with optocoupler OC600 and twelfth resistor R12. Detailed Implementation

[0018] The present invention and its beneficial effects will be further described in detail below with reference to specific embodiments and accompanying drawings. However, the specific embodiments of the present invention are not limited thereto.

[0019] refer to Figures 2-4 This invention provides a short-circuit protection circuit for the output of a switching power supply based on a constant current loop. The circuit includes a sampling circuit 1, an amplification circuit 2, an error amplification circuit 3, and a feedback control circuit 5 connected in sequence. It also includes a trigger circuit 4, the output of which is connected to the first input of the error amplification circuit 3. When the switching power supply output is short-circuited, the trigger circuit 4 reduces the reference voltage of the error amplification circuit 3, thereby lowering the constant current point of the switching power supply. An auxiliary source powers the trigger circuit, ensuring sufficient supply voltage when the switching power supply output is short-circuited.

[0020] In this embodiment, the trigger circuit consists of a trigger module 4-1 and a bypass module 4-2. The bypass module includes an eleventh resistor R11, a first Zener diode D1, a tenth resistor R10, a third capacitor C3, a second capacitor C2, a ninth resistor R9, and a second switching transistor Q2. One end of R11 is connected to the positive terminal of the switching power supply output, and the other end is connected to the cathode of D1. The anode of D1 is connected to the base of Q2, the emitter of Q2 is grounded, and the collector is connected to one end of the ninth resistor R9. The other end of R9 is connected to one end of the second capacitor C2, and the other end of C2 is grounded. The trigger module consists of a fourteenth resistor R14, an eighth resistor R8, a second Zener diode D2, a first switching transistor Q1, a first capacitor C1, and a seventh resistor R7. One end of R14 is connected to the auxiliary source SVCC, and the other end is connected to one end of R8 and one end of the second capacitor C2 of the bypass module. The other end of R8 is connected to the cathode of D2, and the anode of D2 is connected to the base of Q1. C1 is connected to the base and emitter of Q1, with the emitter of Q1 grounded. The collector of Q1 is connected to one end of R7, and the other end of R7 is connected to the non-inverting input of the second operational amplifier U1B. Therefore, when the switching power supply starts up, the auxiliary source SVCC is established first. Before the power supply output voltage Vout is established, SVCC charges C2 after being current-limited by R8. This prevents SVCC from breaking down D2 after being current-limited by R8, causing Q1 to conduct and pull down the voltage at the non-inverting input of the second operational amplifier U1B, thus affecting the normal operation of the power supply. During the charging of C2, the output voltage Vout is established quickly. After Vout is established, it breaks down D1 after being current-limited by R11, causing Q2 to conduct. At this time, C2 discharges quickly through R14 and the collector-emitter junction of Q2 to ground, ensuring that the constant current point can switch rapidly when the switching power supply output short-circuit protection and recovery switch back and forth. When the power supply is operating normally, the voltage at the non-inverting input of the second operational amplifier U1B is Vref1 = Vref * (R6 / (R5 + R6)) ---- Formula 1.

[0021] In this embodiment, the sampling circuit 1 includes an output current sampling resistor connected in series in the output circuit of the switching power supply, and the sampling voltage signal is Vo_cs.

[0022] In this embodiment, the amplifier circuit 2 includes a first resistor R1, a second resistor R2, a third resistor R3, and a first operational amplifier U1A, wherein U1A includes a non-inverting input terminal 3, an inverting input terminal 2, and an output terminal 1. One end of R1 is connected to the current sampling signal, and the other end is connected to the non-inverting input terminal of U1A. One end of R2 is grounded, and the other end is connected to the inverting input terminal of U1A. One end of R3 is connected to the inverting input terminal of U1A, and the other end is connected to the output terminal of U1A. Thus, the current sampling signal is amplified and output as Vo1 = (1 + R3 / R2) * Vo_cs --- Formula 2.

[0023] In this embodiment, the error amplifier circuit 3 includes a second operational amplifier U1B, a thirteenth resistor R13, a fourth capacitor C4, a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6. The second operational amplifier U1B has a non-inverting input 5 and an inverting input 6. The output of the amplifier circuit is current-limited by R4 and then connected to the inverting input of the second operational amplifier U1B. The reference voltage Vref is divided into Vref1 by R5 and R6 and then connected to the non-inverting input of U1B. Thus, in constant current mode, when the output current increases, the output voltage Vo1 of the amplifier circuit increases, causing the output voltage Vo2 of U1B to decrease. Conversely, when the output current decreases, Vo1 decreases, and the output voltage Vo2 of U1B increases.

[0024] In this embodiment, the feedback control circuit 5 includes a twelfth resistor R12 and an optocoupler OC600. The optocoupler OC600 includes a light-emitting diode (LED) anode pin 1, an LED cathode pin 2, a transistor collector pin 4, and an emitter pin 3. The auxiliary source SVCC is current-limited by R12 and connected to pin 1 of OC600. Pin 2 of OC600 is connected to the output of the second operational amplifier U1B. Pin 4 of OC600 is connected to the feedback pin of the control IC, and pin 3 of OC600 is grounded. Thus, in constant current mode, when the output current decreases, causing the output voltage Vo2 of the second operational amplifier U1B to increase, the conduction level of the LED in the optocoupler decreases, the voltage at the FB pin connected to the IC feedback control increases, and the IC increases the duty cycle or frequency of the drive signal, thereby increasing the output current and achieving a constant current effect. Conversely, when the output current increases, the IC decreases the duty cycle or frequency of the drive signal, thereby decreasing the output current and achieving a constant current effect. This is the existing constant current loop control principle, which will not be elaborated further below.

[0025] The working principle of this implementation is as follows: When the switching power supply starts up, the auxiliary source SVCC is established first, while the power supply output voltage Vout is not established. SVCC charges C2 after current limiting and voltage division by R14, preventing SVCC from breaking down D2 after voltage division by R8 and R14, causing Q1 to conduct and pull down the voltage at the non-inverting input of the second operational amplifier U1B, thus affecting the normal operation of the power supply. During the charging of C2, the output voltage Vout will be established quickly. After Vout is established, it breaks down D1 after voltage division and current limiting by R11, causing Q2 to conduct. At this time, C2 is connected to the ground through R9 and the CE terminal of Q2 for rapid discharge, ensuring that the constant current point can switch quickly when the switching power supply output short-circuit protection and recovery switch back and forth. When the power supply is working normally, the voltage at the non-inverting input of the second operational amplifier U1B is Vref1=Vref*(R6 / (R5+R6))----Formula 3, and the constant current point of the switching power supply output is Io1=Vref1 / ((1+(R3 / R2)*R_cs)---Formula 4.

[0026] After a short circuit at the power output, the output voltage is 0, D1 is not broken down, and Q2 is cut off. SVCC, after voltage division and current limiting by R14, rapidly charges C2. When the voltage across C2 is sufficient to break down D2, Q1 turns on. Ignoring the voltage drop across the collector and emitter of Q1 is equivalent to connecting R7 in parallel with R6, thus reducing the voltage across the sixth resistor of the positive input of U1B. At this time, the voltage Vref1 at the non-inverting input of the operational amplifier decreases. According to Equation 4, the constant current point Io1 decreases at this time. Therefore, the constant current point when the switching power supply output is short-circuited is lower than the constant current point during normal operation.

[0027] This invention adds a trigger circuit 4 to a conventional constant current control loop consisting of a sampling circuit 1, an amplifier circuit 2, an error amplifier circuit 3, and a feedback control 5. The output of the trigger circuit 4 is connected to the non-inverting input of the error amplifier circuit 3. Thus, when the switching power supply output is short-circuited, the trigger circuit pulls down the voltage at the non-inverting input of the error amplifier circuit, thereby lowering the constant current point. This invention effectively reduces the constant current point when the switching power supply output is short-circuited, thereby significantly reducing the power losses of the switching power supply devices and improving the reliability of the switching power supply. The circuit structure of this invention is simple and low-cost.

[0028] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0029] Furthermore, all the terms "electrical connection" and "connection" mentioned in this patent application do not refer solely to the direct connection of components, but rather to the ability to form a better connection structure by adding or removing connecting accessories according to the specific implementation. The use of "electrical connection" in this invention is only to emphasize this meaning, but it does not preclude the use of "connection" and other terms from having the same meaning.

Claims

1. A short-circuit protection circuit for the output of a switching power supply based on a constant current loop, comprising a sampling circuit, an amplification circuit, an error amplification circuit, and a feedback control circuit connected in sequence, characterized in that: It also includes a trigger circuit, the output of which is connected to the first input of the error amplifier circuit. When the output of the switching power supply is short-circuited, the trigger circuit reduces the reference voltage of the error amplifier circuit, thereby lowering the constant current point of the switching power supply.

2. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 1, characterized in that: The trigger circuit includes a bypass module and a trigger module. The bypass module is connected to the trigger module. The input terminal of the bypass module is connected to the positive output terminal of the switching power supply. The input terminal of the trigger module is connected to an auxiliary source. The output terminal of the trigger module is connected to the first input terminal of the error amplifier circuit.

3. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 2, characterized in that: The bypass module includes a second capacitor, a ninth resistor, a second switch, a third capacitor, a tenth resistor, a first Zener diode, and an eleventh resistor. The first terminal of the second capacitor is connected to the trigger module and the first terminal of the ninth resistor. The second terminal of the ninth resistor is connected to the first terminal of the second switch. The control terminal of the second switch is connected to the first terminal of the third capacitor, the first terminal of the tenth resistor, and the anode of the first Zener diode. The second terminal of the second switch, the second terminal of the second capacitor, the second terminal of the tenth resistor, and the second terminal of the third capacitor are grounded. The cathode of the first Zener diode is connected to the positive output terminal of the switching power supply through the eleventh resistor.

4. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 2, characterized in that: The trigger module includes a fourteenth resistor, an eighth resistor, a second Zener diode, a first capacitor, a seventh resistor, and a second switching transistor. The first end of the fourteenth resistor is connected to an auxiliary source. The second end of the fourteenth resistor is connected to the first end of the eighth resistor and the bypass module. The second end of the eighth resistor is connected to the cathode of the second Zener diode. The anode of the second Zener diode is connected to the control terminal of the first switching transistor. The first end of the second switching transistor is connected to the first input terminal of the error amplifier circuit through the seventh resistor. The second end of the second switching transistor is grounded. The control terminal of the second switching transistor is grounded through the third capacitor.

5. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 1, characterized in that: The error amplifier circuit includes a second operational amplifier, a thirteenth resistor, a fourth capacitor, a fourth resistor, a fifth resistor, and a sixth resistor. The first terminal of the fourth capacitor is connected to the inverting input terminal of the second operational amplifier, and the second terminal of the fourth capacitor is connected to the output terminal of the second operational amplifier through the thirteenth resistor. The output terminal of the second operational amplifier is connected to the input terminal of the feedback control circuit, and the inverting input terminal of the second operational amplifier is connected to the output terminal of the amplifier circuit through the fourth resistor. The first terminal of the fifth resistor is connected to an auxiliary source, and the second terminal of the fifth resistor is connected to the first terminal of the sixth resistor, the non-inverting input terminal of the second operational amplifier, and the output terminal of the trigger circuit. The second terminal of the sixth resistor is grounded.

6. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 1, characterized in that: The amplification circuit includes a first resistor, a second resistor, a third resistor, and a first operational amplifier; the first end of the third resistor is connected to the output terminal of the first operational amplifier, the second end of the third resistor is connected to the inverting input terminal of the first operational amplifier, the first end of the second resistor is grounded, the second end of the second resistor is connected to the inverting input terminal of the first operational amplifier, the first end of the first resistor is connected to the non-inverting input terminal of the first operational amplifier, the second end of the first resistor is connected to the output terminal of the sampling circuit, and the output terminal of the first operational amplifier is connected to the second input terminal of the error amplifier circuit.

7. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 1, characterized in that: The sampling circuit includes a sampling resistor connected in series in the output circuit of the switching power supply. The first end of the sampling resistor is the current sampling signal point, and the second end of the sampling resistor is grounded.

8. The short-circuit protection circuit for the output of a switching power supply based on a constant current loop according to claim 1, characterized in that: The feedback control circuit includes a twelfth resistor and an optocoupler; the optocoupler includes a first pin, a second pin, a third pin, and a fourth pin; the first end of the twelfth resistor is connected to an auxiliary source, and the second end of the twelfth resistor is connected to the first pin of the optocoupler; the second pin of the optocoupler is connected to the output terminal of the operational amplifier circuit; the third pin of the optocoupler is connected to the ground terminal of the control IC, and the fourth pin of the optocoupler is connected to the feedback control pin of the control IC.

9. A switching power supply, characterized in that: Includes a constant current loop-based switching power supply output short-circuit protection circuit as described in any one of claims 1-8.

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