Protection circuit of switching power supply, switching power supply and power equipment

Abstract

The application relates to a protection circuit of a switching power supply, the switching power supply and a power device, wherein the switching power supply comprises a power supply chip and a flyback power supply circuit; the protection circuit comprises a driving circuit and a switching circuit; the driving circuit can output a driving signal based on a first voltage signal of a control pin of the power supply chip to drive the switching circuit to output a reference voltage to a current sampling pin of the power supply chip so as to make the power supply chip close the output of the flyback power supply circuit, thereby achieving the effect of quickly closing the switching power supply when the output current exceeds a first current threshold, greatly reducing the risk of damage of the switching power supply caused by heat, and improving the safety and stability of the switching power supply.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and in particular relates to a protection circuit for a switching power supply and a switching power supply. Background Technology

[0002] In related technical fields, some switching power supplies, such as flyback auxiliary power circuits, rely on the power supply pins to drop below the minimum operating voltage to control the power chip's shutdown when a short circuit occurs at the output of the single-ended flyback power chip. When the power supply pins are de-energized for an extended period, the short-circuit output windings and rectifier diodes of the flyback switching power supply will experience a prolonged period of high current. This high current can easily cause the insulation of the rectifier diodes and windings to overheat, potentially leading to device damage and affecting the product's safety and stability. Utility Model Content

[0003] The purpose of this application is to provide a protection circuit and a switching power supply, which aims to solve the problem in the related art that the switching power supply has an excessively long shutdown time when the output is short-circuited, which can easily cause device damage and low safety and stability.

[0004] In a first aspect, embodiments of this application provide a protection circuit for a switching power supply, the switching power supply including a power chip and a flyback power supply circuit; the protection circuit includes:

[0005] A driving circuit, wherein the input terminal of the driving circuit is connected to the control pin of the power chip, and the control pin of the power chip is used to output a first voltage signal reaching a first voltage value to the driving circuit when the output current of the flyback power circuit exceeds a first current threshold, and the driving circuit is used to output a driving signal according to the first voltage signal.

[0006] A switching circuit is provided, wherein the control terminal of the switching circuit is connected to the output terminal of the driving circuit, the first terminal of the switching circuit is used to connect to a reference voltage, and the second terminal of the switching circuit is connected to the current sampling pin of the power chip. The switching circuit is used to conduct under the drive signal and output the reference voltage to the current sampling pin of the power chip to control the power chip to turn off the output of the flyback power circuit.

[0007] In some embodiments, the driving circuit includes a delay circuit, which is used to delay the first voltage signal for a preset time before outputting the driving signal.

[0008] In some embodiments, the delay circuit includes a first resistor and a first capacitor, which are connected in series between the control pin and the ground terminal of the power chip, and the series connection node of the first resistor and the first capacitor serves as the output terminal of the drive circuit.

[0009] In some embodiments, the switching circuit includes a first switching transistor and a second switching transistor of the same type;

[0010] The control terminal of the first switching transistor is connected to the control terminal of the switching circuit, the first end of the first switching transistor is connected to the first end of the switching circuit, the second end of the first switching transistor is connected to the control terminal of the second switching transistor, the first end of the second switching transistor is connected to the first end of the first switching transistor, and the second end of the second switching transistor is connected to the second end of the switching circuit.

[0011] In some embodiments, both the first switching transistor and the second switching transistor are PNP transistors, with the base of the PNP transistor forming the control terminal of the corresponding switch; the emitter of the PNP transistor forming the first terminal of the corresponding switching transistor, and the collector of the PNP transistor forming the second terminal of the corresponding switching transistor.

[0012] In some embodiments, at least one of a first current limiting circuit, a filter circuit, and a second current limiting circuit is also included;

[0013] The first current limiting circuit is connected between the output terminal of the drive circuit and the control terminal of the switching circuit.

[0014] The filter circuit is connected between the output terminal of the drive circuit and the control terminal of the switch circuit.

[0015] The second current limiting circuit is connected between the control terminal and the ground terminal of the second switching transistor.

[0016] In some embodiments, the first terminal of the switching circuit is connected to the reference voltage pin of the power chip to receive the reference voltage.

[0017] Secondly, one embodiment of this application also provides a switching power supply, including a power chip and a flyback power circuit; the power chip is used to control the flyback power circuit; the switching power supply also includes the protection circuit as described above.

[0018] In some embodiments, the flyback power supply circuit includes a transformer, a power switch, an output circuit, a sampling circuit, and a feedback circuit.

[0019] The first end of the primary winding of the transformer is used to connect to a power supply, and the first end of the power switch is connected to the second end of the primary winding. The second end of the power switch is connected to the current sampling pin of the power chip and grounded through the sampling circuit. The drive pin of the power chip is connected to the control terminal of the power switch. The secondary winding of the transformer is connected to the output circuit, and the feedback circuit is connected to the output circuit and the control pin. The feedback circuit is used to output a first voltage signal reaching a first voltage value to the control pin of the power chip when the output current of the output circuit exceeds a first current threshold.

[0020] Thirdly, one embodiment of this application also provides a power device, including the aforementioned switching power supply.

[0021] The beneficial effects of this application embodiment compared with related technologies are as follows: The protection circuit includes a drive circuit and a switching circuit. When the output current of the flyback power circuit of the switching power supply exceeds the first current threshold, the drive circuit can output a drive signal based on the first voltage signal of the control pin of the power chip of the switching power supply. The drive switching circuit outputs the reference voltage to the current sampling pin of the power chip, so that the power chip shuts down the output of the flyback power circuit. This achieves the effect of quickly shutting down the switching power supply when the output current exceeds the first current threshold, greatly reducing the risk of damage to the switching power supply due to heat generation and improving the safety and stability of the switching power supply. Attached Figure Description

[0022] Figure 1 This is a circuit diagram of a switching power supply according to an embodiment of this application.

[0023] Figure 2 This is a schematic diagram of a protection circuit for a switching power supply provided in an embodiment of this application.

[0024] Figure 3 A circuit diagram of a protection circuit for a switching power supply provided in an embodiment of this application. Detailed Implementation

[0025] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0026] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0028] Please see Figure 1 One embodiment of this application provides a switching power supply applicable to any electrical device, such as an adapter, energy storage device, or power device. The switching power supply includes a power chip 100 and a flyback power circuit. The power chip 100 controls the flyback power circuit, and the switching power supply also includes a protection circuit 210.

[0029] The protection circuit 210 of the switching power supply can output a drive signal based on the first voltage signal of the control pin COMP of the power chip 100 when the output current of the flyback power circuit exceeds the first current threshold. The reference voltage Vref is output to the current sampling pin CS of the power chip 100, so that the power chip 100 shuts down the output of the flyback power circuit. This achieves the effect of quickly shutting down the switching power supply when the output current exceeds the first current threshold, greatly reducing the risk of damage to the switching power supply due to heat and improving the safety and stability of the switching power supply.

[0030] In some embodiments, the flyback power supply circuit includes a transformer, a power switch Q1, an output circuit 220, a sampling circuit 230, and a feedback circuit 240. The first end of the primary winding Np1 of the transformer is connected to the power supply Vin, and the first end of the power switch Q1 is connected to the second end of the primary winding Np1. The second end of the power switch Q1 is connected to the current sampling pin CS of the power chip 100 and grounded through the sampling circuit 230. The drive pin out of the power chip 100 is connected to the control terminal of the power switch Q1. The secondary winding Ns1 of the transformer is connected to the output circuit 220. The feedback circuit 240 is connected to the output circuit 220 and the control pin COMP of the power chip 100. The feedback circuit 240 is used to output a first voltage signal reaching a first voltage value to the control pin COMP of the power chip 100 when the output current of the output circuit 220 exceeds a first current threshold.

[0031] For example, the power supply Vin is direct current (DC). This DC power can be obtained by rectifying an AC power supply through a rectifier bridge, or it can be directly provided by a DC power supply. The power switch Q1 is an N-channel MOSFET, with its drain, source, and gate being the first terminal, second terminal, and control terminal, respectively. The sampling circuit 230 includes a sampling resistor Rcs, which is connected between the source of the MOSFET Q1 and the ground terminal. The drive pin out of the power chip 100 outputs a pulse width modulation (PWM) signal. When the PWM signal controls the MOSFET Q1 to turn on, the inductor current in the primary winding Np1 of the transformer begins to rise and store energy. When the PWM signal controls the MOSFET Q1 to turn off, the primary winding Np1 of the transformer releases energy and couples it to the secondary winding Ns1 of the transformer, and outputs it from the output circuit 220.

[0032] The first current threshold is a reference value used to determine whether a short circuit occurs at the output. It can be set to the current value at the time of the short circuit, or it can be set to a value lower than this current value, depending on the actual needs. When the output current exceeds the first current threshold, a short circuit can be determined at the output. The first voltage value can be the voltage value corresponding to a high-level signal, and it can be configured according to the actual situation. It can be understood that when the feedback circuit 240 does not experience a short circuit fault in the output circuit 220, it will output a second voltage signal of the second voltage value to the control pin COMP of the power chip 100. At this time, the power chip 100 will control the flyback power supply circuit to output normally according to the second voltage signal.

[0033] In some embodiments, the output circuit 220 includes a rectifier diode D1 and an output capacitor C1. The anode of the rectifier diode D1 is connected to the first terminal of the secondary winding Ns1 of the transformer, and the cathode of the rectifier diode D1 constitutes the positive output terminal of the output circuit 220. The second terminal of the secondary winding Ns1 of the transformer constitutes the negative output terminal of the output circuit 220, and the output capacitor C1 is connected between the positive and negative output terminals.

[0034] In some embodiments, the feedback loop includes voltage divider resistors R1 and R2, a controllable precision voltage regulator SCR1, resistors R3 and R4, and an optocoupler U1. Voltage divider resistors R1 and R2 are connected in series between the positive and negative output terminals of the output circuit 220. The positive terminal of the light source of optocoupler U1 is connected to the positive output terminal of the output circuit 220 through resistor R3; the negative terminal of the light source of optocoupler U1 is connected to the cathode of the controllable precision voltage regulator SCR1; the anode of the controllable precision voltage regulator SCR1 is connected to the negative output terminal, and the reference terminal of the controllable precision voltage regulator SCR1 is connected to the series node of voltage divider resistors R1 and R2. The positive terminal of the photodetector of optocoupler U1 is connected to the reference voltage Vref through resistor R4, and the positive terminal of the photodetector of optocoupler U1 is also connected to the control pin COMP of the power chip 100; the negative terminal of the photodetector of optocoupler U1 is grounded.

[0035] It is understood that in the embodiments of this application, the negative terminal of the input side of the switching power supply constitutes the input side ground terminal GND1, and the negative terminal of the output circuit 220 constitutes the output side ground terminal GND2.

[0036] In some embodiments, the flyback power supply circuit further includes a power supply circuit 250 for the power chip 100, located on the input side of the switching power supply. The power supply circuit 250 includes an auxiliary winding Np2 of the transformer, a diode D2, a capacitor C2, and a starting resistor R5. The anode of diode D2 is connected to the first terminal of the auxiliary winding Np2, the second terminal of the auxiliary winding Np2 is grounded, and the anode of diode D2 is connected to the power supply pin VCC of the power chip 100. One end of the starting resistor R5 is connected to the power supply Vin, and the other end is connected to the power supply pin VCC of the power chip 100.

[0037] For example, with a reference voltage Vref of 5V, when the output Vout of the switching power supply is not short-circuited, the controllable precision voltage regulator SCR1 conducts based on the voltage of the voltage divider resistor R2, and the optocoupler U1 conducts. Based on the voltage division of resistor R4 and optocoupler U1, the voltage range of the control pin COMP of the power supply chip 100 is, for example, 2.5V to 4V. When the output Vout of the switching power supply is short-circuited, there is no current in the voltage divider resistor R2, the controllable precision voltage regulator SCR1 is cut off, the optocoupler U1 is turned off, and the reference voltage Vref is supplied to the control pin COMP of the power supply chip 100 through resistor R4, causing the control pin COMP to be pulled high to a first voltage value, for example, a first voltage signal greater than 4V. A typical first voltage value can be set to 4.3V.

[0038] Please see Figure 2In some embodiments, the protection circuit 210 of the switching power supply includes a drive circuit 211 and a switching circuit 212. The input terminal of the drive circuit 211 is connected to the control pin COMP of the power chip 100. The control pin COMP of the power chip 100 is used to output a first voltage signal reaching a first voltage value to the drive circuit 211 when the output current of the flyback power supply circuit exceeds a first current threshold. The drive circuit 211 is used to output a drive signal according to the first voltage signal. The control terminal of the switching circuit 212 is connected to the output terminal of the drive circuit 211. The first terminal of the switching circuit 212 is used to connect to a reference voltage Vref. The second terminal of the switching circuit 212 is connected to the current sampling pin CS of the power chip 100. The switching circuit 212 is used to turn on under the drive signal, outputting the reference voltage Vref to the current sampling pin CS of the power chip 100 to control the power chip 100 to turn off the output of the flyback power supply circuit.

[0039] In this embodiment, when the control pin COMP of the power chip 100 is short-circuited, for example, the voltage rises to a first voltage value, thereby providing a first voltage signal to the drive circuit 211. The drive circuit 211 outputs a drive signal based on the first voltage signal, and drives the switching circuit 212 to output the reference voltage Vref to the current sampling pin CS of the power chip 100, thereby triggering the short-circuit protection of the power chip 100, entering the wave blocking state, and shutting down the output of the flyback power supply circuit. This greatly reduces the risk of damage to the switching power supply due to heat and improves the safety and stability of the switching power supply.

[0040] In some embodiments, the driving circuit 211 includes a delay circuit, which delays the first voltage signal for a preset time before outputting a driving signal. Adding a delay function helps avoid accidentally triggering the short-circuit protection of the power supply chip 100 and shutting down the output of the flyback power supply circuit. Optionally, the delay circuit implements the delay based on the first voltage signal lasting for at least a preset time.

[0041] Please see Figure 3 In some embodiments, the delay circuit includes a first resistor R6 and a first capacitor C3. The first resistor R6 and the first capacitor C3 are connected in series between the control pin COMP of the power supply chip 100 and the ground terminal. The series connection of the first resistor R6 and the first capacitor C3 serves as the output terminal of the drive circuit 211. It is understood that the values ​​of the first resistor R6 and the first capacitor C3 can adjust the preset delay duration. The drive signal is the first voltage signal output after the preset delay duration.

[0042] In other embodiments, the driving circuit 211 may be configured with a voltage divider network and a switching transistor. The voltage divider network divides the first voltage signal to obtain a voltage component, which drives the switching transistor to turn on and output a driving signal.

[0043] Please see Figure 3 In some embodiments, the switching circuit 212 includes a first switching transistor M1 and a second switching transistor M2 of the same type. The control terminal of the first switching transistor M1 is connected to the control terminal of the switching circuit 212, the first end of the first switching transistor M1 is connected to the first end of the switching circuit 212, the second end of the first switching transistor M1 is connected to the control terminal of the second switching transistor M2, the first end of the second switching transistor M2 is connected to the first end of the first switching transistor M1, and the second end of the second switching transistor M2 is connected to the second end of the switching circuit 212. In this embodiment, the states of the first switching transistor M1 and the second switching transistor M2 are opposite. When the first switching transistor M1 is turned off under the drive of a drive signal generated by a first voltage signal based on a first voltage value, the second switching transistor M2 will be turned on, connecting the reference voltage Vref at the first end of the switching circuit 212 to the current sampling pin CS of the power supply chip 100. Conversely, if no drive signal is received, that is, when the control pin COMP outputs a control signal, the first switching transistor M1 will be turned on, the second switching transistor M2 will be turned off, and no reference voltage Vref will be connected to the current sampling pin CS of the power supply chip 100. The switching circuit 212 adopts this simple circuit structure, with fewer components, which can reduce costs and increase efficiency, and is conducive to miniaturization.

[0044] In some embodiments, both the first switching transistor M1 and the second switching transistor M2 are PNP transistors. The base of the PNP transistor constitutes the control terminal of the corresponding switch; the emitter of the PNP transistor constitutes the first terminal of the corresponding switching transistor, and the collector of the PNP transistor constitutes the second terminal of the corresponding switching transistor. For example, when the control pin COMP of the power supply chip 100 is pulled high to above 4.3V, this level charges the first capacitor C3 through the first resistor R6. Once the voltage of the first capacitor C3 reaches 4.3V, the first switching transistor M1 is turned off. The base potential of the second switching transistor M2 is 0V, the second switching transistor M2 is turned on, and the current sampling pin CS of the power supply chip 100 is pulled high to the reference voltage Vref, and the power supply chip 100 enters a waveform blocking state.

[0045] In some embodiments, the protection circuit 210 of the switching power supply further includes a first current limiting circuit R7. The first current limiting circuit R7 is connected between the output terminal of the drive circuit 211 and the control terminal of the switching circuit 212, and is used to limit the current at the control terminal of the switching circuit 212 to provide protection. For example, the first current limiting circuit R7 includes a current limiting resistor.

[0046] In some embodiments, the protection circuit 210 of the switching power supply further includes a filter circuit C4, which is connected between the output terminal of the drive circuit 211 and the control terminal of the switching circuit 212. The filter circuit C4 filters out interference from the control terminal of the switching circuit 212, ensuring accurate control of the switching circuit 212 and providing a certain degree of protection. For example, the filter circuit C4 includes a filter capacitor.

[0047] In some embodiments, the protection circuit 210 of the switching power supply further includes a second current-limiting circuit R8. The second current-limiting circuit R8 is connected between the control terminal of the second switching transistor M2 and the ground terminal, providing bias to the control terminal of the second switching transistor M2 and simultaneously acting as a current limiter. Exemplarily, the second current-limiting circuit R8 includes a current-limiting resistor.

[0048] In some embodiments, a current-limiting resistor is connected between the control terminal of the second switch M2 and the second terminal of the first switch M1.

[0049] In some embodiments, the first terminal of the switching circuit 212 is connected to the reference voltage pin of the power supply chip 100 to receive the reference voltage Vref, i.e., the reference voltage Vref is directly provided by the power supply chip 100. In other embodiments, the reference voltage Vref may be provided by a separately configured reference voltage source.

[0050] Compared to traditional flyback power supplies, the switching power supply of this application embodiment can quickly shut down the power chip 100 in the event of an output short circuit. This greatly reduces the heating of the rectifier diode D1 and the secondary winding Ns1 copper wire in the output circuit 220, significantly reducing the risk of damage to the device and personal safety risks caused by overheating. It also has the advantages of fewer components, smaller board area, and significant advantages in reliability and cost.

[0051] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A protection circuit for a switching power supply, characterized by The switching power supply includes a power chip and a flyback power circuit; the protection circuit includes: A driving circuit, wherein the input terminal of the driving circuit is connected to the control pin of the power chip, and the control pin of the power chip is used to output a first voltage signal reaching a first voltage value to the driving circuit when the output current of the flyback power circuit exceeds a first current threshold, and the driving circuit is used to output a driving signal according to the first voltage signal. A switching circuit is provided, wherein the control terminal of the switching circuit is connected to the output terminal of the driving circuit, the first terminal of the switching circuit is used to connect to a reference voltage, and the second terminal of the switching circuit is connected to the current sampling pin of the power chip. The switching circuit is used to conduct under the drive signal and output the reference voltage to the current sampling pin of the power chip to control the power chip to turn off the output of the flyback power circuit.

2. The protection circuit of claim 1, wherein, The driving circuit includes a delay circuit, which is used to delay the first voltage signal for a preset time before outputting the driving signal.

3. The protection circuit of claim 2, wherein, The delay circuit includes a first resistor and a first capacitor, which are connected in series between the control pin and the ground terminal of the power chip. The series connection node of the first resistor and the first capacitor serves as the output terminal of the drive circuit.

4. The protection circuit according to claim 1 or 2, wherein The switching circuit includes a first switching transistor and a second switching transistor of the same type; The control terminal of the first switching transistor is connected to the control terminal of the switching circuit, the first end of the first switching transistor is connected to the first end of the switching circuit, the second end of the first switching transistor is connected to the control terminal of the second switching transistor, the first end of the second switching transistor is connected to the first end of the first switching transistor, and the second end of the second switching transistor is connected to the second end of the switching circuit.

5. The protection circuit of claim 4, wherein, Both the first and second switching transistors are PNP transistors. The base of the PNP transistor forms the control terminal of the corresponding switch. The emitter of the PNP transistor forms the first terminal of the corresponding switching transistor, and the collector of the PNP transistor forms the second terminal of the corresponding switching transistor.

6. The protection circuit of claim 4, wherein, It also includes at least one of a first current limiting circuit, a filter circuit, and a second current limiting circuit; The first current limiting circuit is connected between the output terminal of the drive circuit and the control terminal of the switching circuit. The filter circuit is connected between the output terminal of the drive circuit and the control terminal of the switch circuit. The second current limiting circuit is connected between the control terminal and the ground terminal of the second switching transistor.

7. The protection circuit as described in claim 1, characterized in that, The first terminal of the switching circuit is connected to the reference voltage pin of the power chip to receive the reference voltage.

8. A switching power supply, characterized in that, It includes a power supply chip and a flyback power supply circuit; the power supply chip is used to control the flyback power supply circuit; the switching power supply also includes a protection circuit as described in any one of claims 1 to 7.

9. The switching power supply as described in claim 8, characterized in that, The flyback power supply circuit includes a transformer, a power switch, an output circuit, a sampling circuit, and a feedback circuit. The first end of the primary winding of the transformer is used to connect to a power supply, and the first end of the power switch is connected to the second end of the primary winding. The second end of the power switch is connected to the current sampling pin of the power chip and grounded through the sampling circuit. The drive pin of the power chip is connected to the control terminal of the power switch. The secondary winding of the transformer is connected to the output circuit. The feedback circuit is connected to the output circuit and the control pin of the power chip. The feedback circuit is used to output a first voltage signal reaching a first voltage value to the control pin of the power chip when the output current of the output circuit exceeds a first current threshold.

10. An electrical device, characterized in that, Includes the switching power supply as described in claim 8 or 9.

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