An undervoltage protection circuit and a flyback power supply circuit

Abstract

The present application discloses an undervoltage protection circuit and a flyback power supply circuit. The undervoltage protection circuit includes: a driver chip; a voltage comparison subcircuit, a first input end for receiving a reference voltage, a second input end electrically connected to the input end of a flyback converter, and a voltage comparison subcircuit outputting a first level in response to the input voltage of the flyback converter being lower than the reference voltage; a first switch module, a control end electrically connected to the output end of the voltage comparison subcircuit, a first end electrically connected to the fault feedback end of the driver chip, and a second end electrically connected to the ground end, the first switch module is turned on in response to the first level, and the fault feedback end of the driver chip is connected to the ground end; the driver chip enters a locked state in response to the fault feedback end of the driver chip being connected to the ground end, so that the drive signal output end of the driver chip does not send a drive signal to the flyback converter. The embodiment of the present application can protect the flyback converter when the input voltage is too low.

Description

Technical Field

[0001] The present application belongs to the technical field of electronic circuits, and in particular relates to an undervoltage protection circuit and a flyback power supply circuit. Background Art

[0002] Usually, when designing a flyback converter, the minimum input voltage and maximum output power are generally used as the limit operating conditions. When the input voltage is lower than the designed minimum input voltage, the duty cycle of the flyback converter when working at full load may exceed the designed limit value, resulting in abnormal output of the switching power supply; in addition, if the input voltage is too low, when running at full load, the current flowing through the flyback converter is too large, which will increase the loss of the switching power supply and reduce the efficiency. In severe cases, it will cause the thermal design of the power supply to fail. Utility Model Content

[0003] The embodiments of the present application provide an undervoltage protection circuit and a flyback power supply circuit, which can protect a flyback converter when the input voltage is too low.

[0004] In a first aspect, an embodiment of the present application provides an undervoltage protection circuit, which includes: a driver chip; a voltage comparison subcircuit, a first input end of the voltage comparison subcircuit is used to receive a reference voltage, a second input end of the voltage comparison subcircuit is electrically connected to the input end of the flyback converter, and the voltage comparison subcircuit is used to output a first level in response to the input voltage of the flyback converter being lower than the reference voltage; a first switch module, a control end of the first switch module is electrically connected to the output end of the voltage comparison subcircuit, a first end of the first switch module is electrically connected to a fault feedback end of the driver chip, a second end of the first switch module is electrically connected to a ground end, and the first switch module is used to be turned on in response to the first level, connecting the fault feedback end of the driver chip to the ground end; the driver chip is used to enter a locked state in response to the fault feedback end of the driver chip being connected to the ground end, so that the drive signal output end of the driver chip does not send a drive signal to the flyback converter.

[0005] According to the implementation scheme of the first aspect of the present application, the undervoltage protection circuit also includes: a linear voltage stabilization sub-circuit, a first end of the linear voltage stabilization sub-circuit is electrically connected to the power input end of the driving chip and the chip power supply end of the flyback converter, a second end of the linear voltage stabilization sub-circuit is electrically connected to the first input end of the voltage comparison sub-circuit, and the linear voltage stabilization sub-circuit provides a reference voltage for the voltage comparison sub-circuit through the second end.

[0006] According to any of the aforementioned embodiments of the first aspect of the present application, the voltage comparison subcircuit includes: a first voltage dividing module, a first end of the first voltage dividing module is electrically connected to the second end of the linear voltage stabilization subcircuit; a second voltage dividing module, a first end of the second voltage dividing module is electrically connected to the second end of the first voltage dividing module, and the second end of the second voltage dividing module is electrically connected to the ground end; a first capacitor, a first end of the first capacitor is electrically connected to the second end of the first voltage dividing module and the first end of the second voltage dividing module, and the second end of the first capacitor is electrically connected to the ground end; a comparator, a power supply end of the comparator is electrically connected to the second end of the linear voltage stabilization subcircuit, a first input end of the comparator is electrically connected to the second end of the first voltage dividing module, the first end of the second voltage dividing module and the first end of the first capacitor, the ground end of the comparator is electrically connected to the ground end, and the output end of the comparator is electrically connected to the control end of the first switch module; A third voltage-dividing module, wherein the first end of the third voltage-dividing module is electrically connected to the positive voltage input end of the flyback converter, and the second end of the third voltage-dividing module is electrically connected to the second input end of the comparator; a fourth voltage-dividing module, wherein the first end of the fourth voltage-dividing module is electrically connected to the second end of the third voltage-dividing module, and the second end of the fourth voltage-dividing module is electrically connected to the negative voltage input end of the flyback converter and the ground end; a second capacitor, wherein the first end of the second capacitor is electrically connected to the second end of the third voltage-dividing module and the second input end of the comparator, and the second end of the second capacitor is electrically connected to the ground end; a pull-up resistor, wherein the first end of the pull-up resistor is electrically connected to the second end of the linear voltage stabilization subcircuit, and the second end of the pull-up resistor is electrically connected to the control end of the first switch module and the output end of the comparator; and a third capacitor, wherein the first end of the third capacitor is electrically connected to the second end of the pull-up resistor, and the second end of the third capacitor is electrically connected to the ground end.

[0007] According to any of the aforementioned embodiments of the first aspect of the present application, the linear voltage stabilization subcircuit includes: a transistor, a first end of the transistor is electrically connected to the power input end of the driving chip; a driving resistor, a first end of the driving resistor is electrically connected to the control end of the transistor, and a second end of the driving resistor is electrically connected to the first end of the transistor; a first voltage stabilization module, a first end of the first voltage stabilization module is electrically connected to the control end of the transistor, and a second end of the first voltage stabilization module is electrically connected to the ground end; a fifth voltage divider module, a first end of the fifth voltage divider module is electrically connected to the second end of the transistor, and a second end of the fifth voltage divider module is electrically connected to the third end of the first voltage stabilization module; a sixth voltage divider module, a first end of the sixth voltage divider module is electrically connected to the second end of the fifth voltage divider module and the third end of the first voltage stabilization module, and a second end of the sixth voltage divider module is electrically connected to the ground end; a first decoupling module, a first end of the first decoupling module is electrically connected to the second end of the driving resistor, and a second end of the first decoupling module is electrically connected to the ground end.

[0008] According to any of the aforementioned embodiments of the first aspect of the present application, the undervoltage protection circuit also includes: a voltage limiting sub-circuit, a first end of the voltage limiting sub-circuit is electrically connected to the input end of the flyback converter, a second end of the voltage limiting sub-circuit is electrically connected to the high voltage input end of the driver chip, a third end of the voltage limiting sub-circuit is electrically connected to the ground end, and the voltage limiting sub-circuit is used to limit the voltage input to the driver chip; a fourth capacitor, a first end of the fourth capacitor is electrically connected to the power input end of the driver chip, and a second end of the fourth capacitor is electrically connected to the ground end and the ground end of the driver chip.

[0009] According to any of the aforementioned embodiments of the first aspect of the present application, the voltage limiting subcircuit includes: a current limiting module, a first end of the current limiting module is electrically connected to the input end of the flyback converter; an overvoltage protection module, a first end of the overvoltage protection module is electrically connected to the second end of the current limiting module, and the second end of the overvoltage protection module is electrically connected to the ground end; a second switch module, a control end of the second switch module is electrically connected to the first end of the overvoltage protection module, and the first end of the switch module is electrically connected to the first end of the current limiting module; a seventh voltage divider module, a first end of the seventh voltage divider module is electrically connected to the second end of the second switch module; a first reverse cutoff module, a first end of the first reverse cutoff module is electrically connected to the second end of the seventh voltage divider module, and the second end of the first reverse cutoff module is electrically connected to the high voltage input end of the driver chip.

[0010] According to any of the aforementioned embodiments of the first aspect of the present application, the voltage limiting subcircuit also includes: a second decoupling module, a first end of the second decoupling module is electrically connected to the first end of the overvoltage protection module and the control end of the second switch module, and a second end of the second decoupling module is electrically connected to the first end of the seventh voltage dividing module; an eighth voltage dividing module, a first end of the eighth voltage dividing module is electrically connected to the first end of the second decoupling module, and a second end of the eighth voltage dividing module is electrically connected to the first end of the seventh voltage dividing module; a second voltage stabilizing module, a first end of the second voltage stabilizing module is electrically connected to the first end of the second decoupling module, and a second end of the second voltage stabilizing module is electrically connected to the first end of the seventh voltage dividing module.

[0011] In a second aspect, an embodiment of the present application provides a flyback power supply circuit, the flyback power supply circuit comprising: a flyback converter; and an undervoltage protection circuit such as the first aspect, the undervoltage protection circuit being electrically connected to the flyback converter.

[0012] According to the implementation scheme of the second aspect of the present application, the flyback converter includes: a third switch module, the control end of the third switch module is electrically connected to the drive signal output end of the driving chip of the undervoltage protection circuit; a first transformer, the first end of the first primary winding of the first transformer is electrically connected to the positive voltage power supply end, the second end of the first primary winding is electrically connected to the first end of the third switch module, and the first secondary winding of the first transformer is electrically connected to the output end; a fourth switch module, the control end of the fourth switch module is electrically connected to the drive signal output end of the driving chip; a second transformer, the first end of the second primary winding of the second transformer is electrically connected to the second end of the third switch module, the second end of the second primary winding is electrically connected to the first end of the fourth switch module, and the second secondary winding of the second transformer is electrically connected to the power input end of the driving chip of the undervoltage protection circuit.

[0013] According to any of the aforementioned embodiments of the second aspect of the present application, the flyback power supply circuit also includes: a second reverse cutoff module, a first end of the second reverse cutoff module is electrically connected to the first end of the first primary winding, and a second end of the second reverse cutoff module is electrically connected to the positive voltage input terminal; a third decoupling module, a first end of the third decoupling module is electrically connected to the second end of the second reverse cutoff module and the positive voltage input terminal; a first sampling module, a first end of the first sampling module is electrically connected to the second end of the third switching module, and the second end of the first sampling module is electrically connected to the second end of the third decoupling module; a third reverse cutoff module, a first end of the third reverse cutoff module is electrically connected to the first end of the second primary winding, and the second end of the third reverse cutoff module is electrically connected to the second end of the third decoupling module and the high voltage input terminal of the driving chip; a fourth decoupling module, a first end of the fourth decoupling module is electrically connected to the first end of the second primary winding and the second section of the third decoupling module, and the fourth decoupling module The second end of the module is electrically connected to the ground end; the second sampling module, the first end of the second sampling module is electrically connected to the second end of the fourth switch module, and the second end of the second sampling module is electrically connected to the ground end; the fourth reverse cut-off module, the first end of the fourth reverse cut-off module is electrically connected to the first end of the first secondary winding, and the second end of the fourth reverse cut-off module is electrically connected to the output end; the fifth decoupling module, the first end of the fifth decoupling module is electrically connected to the second end of the fourth reverse cut-off module, and the second end of the fifth decoupling module is electrically connected to the second end of the first secondary winding; the fifth reverse cut-off module, the first end of the fifth reverse cut-off module is electrically connected to the first end of the second secondary winding, and the second end of the fifth reverse cut-off module is electrically connected to the power input end of the driving chip; the sixth decoupling module, the first end of the sixth decoupling module is electrically connected to the second end of the fifth reverse cut-off module, and the second end of the sixth decoupling module is electrically connected to the ground end and the second end of the second secondary winding.

[0014] The undervoltage protection circuit and flyback power supply circuit of the embodiment of the present application compare the input voltage of the flyback converter with the reference voltage through the voltage comparison subcircuit, and when the input voltage is lower than the reference voltage, output the first level to control the first switch module to turn on. Since the first end of the first switch module is electrically connected to the fault feedback end of the driver chip, and the second end of the first switch module is electrically connected to the ground end, when the first level controls the first switch module to turn on, the fault feedback end of the driver chip is connected to the ground end, so that the driver chip enters a locked state, thereby realizing that the drive signal output end of the driver chip does not send a drive signal to the flyback converter. The flyback converter does not work if it does not receive the drive signal, so that when the input voltage is too low, the flyback converter does not work, thereby realizing the protection of the flyback converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 This is a circuit connection diagram of the undervoltage protection circuit provided in an embodiment of the present application;

[0017] Figure 2 is another circuit connection schematic diagram of the undervoltage protection circuit provided in an embodiment of the present application;

[0018] Figure 3 This is another circuit connection diagram of the undervoltage protection circuit provided in the embodiment of the present application;

[0019] Figure 4 It is a circuit connection diagram of a flyback power supply circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0020] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0021] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0022] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0023] In the embodiments of the present application, the term “electrically connected” may refer to a direct electrical connection between two components, or may refer to an electrical connection between two components via one or more other components.

[0024] It is obvious to those skilled in the art that various modifications and changes can be made in the present application without departing from the spirit or scope of the present application. Therefore, the present application is intended to cover modifications and changes of the present application that fall within the scope of the corresponding claims (technical solutions for protection) and their equivalents. It should be noted that the implementation methods provided in the embodiments of the present application can be combined with each other without contradiction.

[0025] Before describing the technical solutions provided by the embodiments of the present application, in order to facilitate the understanding of the embodiments of the present application, the present application first specifically describes the problems existing in the related art:

[0026] Flyback converters are widely used in switching power supplies due to their low cost, wide voltage conversion range, and easy control. At present, there are many integrated flyback power supply control chips on the market, among which QR control chips represented by NCP1342 chips can help flyback converters work in a quasi-resonant state to a certain extent, reduce converter losses, and are widely used in flyback power supplies.

[0027] It should be noted that when designing a flyback converter, the minimum input voltage and maximum output power are generally used as the limit operating conditions. When the input voltage is lower than the designed minimum input voltage, the duty cycle of the flyback converter when working at full load may exceed the designed limit value, resulting in abnormal output of the switching power supply; in addition, if the input voltage is too low, when running at full load, the current flowing through the flyback converter is too large, which will increase the loss of the switching power supply and reduce the efficiency. In severe cases, it will cause the thermal design of the power supply to fail.

[0028] In order to solve the above technical problems, the embodiments of the present application provide an undervoltage protection circuit and a flyback power supply circuit. The undervoltage protection circuit provided by the embodiments of the present application is first introduced below.

[0029] Figure 1 is a circuit connection diagram of an undervoltage protection circuit provided in an embodiment of the present application, such as Figure 1 As shown, the undervoltage protection circuit 100 may include: a driving chip 110 , a voltage comparison subcircuit 120 and a first switch module 130 .

[0030] The first input terminal of the voltage comparison subcircuit 120 is used to receive the reference voltage VREF, and the second input terminal of the voltage comparison subcircuit 120 is electrically connected to the input terminal of the flyback converter 200. The voltage comparison subcircuit 120 is used to output a first level in response to the input voltage VIN of the flyback converter 200 being lower than the reference voltage VREF.

[0031] The control end of the first switch module 130 is electrically connected to the output end of the voltage comparison sub-circuit 120, the first end of the first switch module 130 is electrically connected to the fault feedback end FAULT of the driver chip 110, and the second end of the first switch module 130 is electrically connected to the ground end GND. The first switch module 130 is used to be turned on in response to the first level, connecting the fault feedback end FAULT of the driver chip to the ground end GND.

[0032] The present application achieves the purpose of controlling the FAULT terminal potential by controlling the on and off of the first switch module 130 .

[0033] The driver chip 110 is used to enter a locked state in response to the fault feedback terminal FAULT of the driver chip 110 being connected to the ground terminal GND, so that the drive signal output terminal Drive of the driver chip 110 does not send a drive signal to the flyback converter 200 .

[0034] In some specific embodiments, the first switch module 130 may be an NMOS transistor or a PMOS transistor. Figure 1Taking the first switching module as the NMOS transistor Q1 for illustration, at this time, the first level is a high level, that is, when VIN < VREF, the voltage comparator sub-circuit 120 outputs a high level, the NMOS transistor Q1 conducts, and the FAULT terminal of the driving chip is grounded. The driving chip 110 can be an NCP1342 chip. It should be noted that when the potential of the FAULT terminal of the NCP1342 chip is lower than 400 mV, the chip is locked and does not generate waves, and the power supply does not work. Therefore, when the FAULT terminal of the driving chip is grounded, the driving chip 110 enters the locked state. Correspondingly, when the first switching module 130 is a PMOS transistor, the first level is a low level.

[0035] The NCP1342 chip can help the flyback converter 200 work in the quasi-resonant state to a certain extent, reduce the loss of the flyback converter 200, and is widely used in the flyback power supply circuit.

[0036] The undervoltage protection circuit 100 of the embodiment of the present application compares the input voltage VIN of the flyback converter 200 with the reference voltage VREF through the voltage comparator sub-circuit 120, and outputs the first level to control the first switching module 130 to turn on when the input voltage VIN is lower than the reference voltage VREF. Since the first terminal of the first switching module 130 is electrically connected to the fault feedback terminal FAULT of the driving chip, and the second terminal of the first switching module 130 is electrically connected to the ground terminal GND, when the first level controls the first switching module 130 to turn on, the fault feedback terminal FAULT of the driving chip 110 is connected and conducted to the ground terminal GND, so that the driving chip 110 enters the locked state, and further the drive signal output terminal Drive of the driving chip does not send a drive signal to the flyback converter 200. The flyback converter 200 does not work without receiving the drive signal, so that when the input voltage VIN is too low, the flyback converter 200 does not work, and the protection of the flyback converter 200 is realized.

[0037] Figure 2 It is another circuit connection diagram of the undervoltage protection circuit provided by the embodiment of the present application. As Figure 2 shown, the undervoltage protection circuit 100 may further include: a linear voltage regulator sub-circuit 140 and a voltage limiting sub-circuit 150.

[0038] The first terminal of the linear voltage regulator sub-circuit 140 is electrically connected to the power input terminal VCC of the driving chip and the chip power supply terminal of the flyback converter 200. The second terminal of the linear voltage regulator sub-circuit 140 is electrically connected to the first input terminal of the voltage comparator sub-circuit 120. The linear voltage regulator sub-circuit 140 provides the reference voltage VREF for the voltage comparator sub-circuit through the second terminal.

[0039] The first end of the voltage limiting sub-circuit 150 is electrically connected to the input end of the flyback converter 200, the second end of the voltage limiting sub-circuit 150 is electrically connected to the high voltage input end HV of the driver chip 110, and the third end of the voltage limiting sub-circuit 150 is electrically connected to the ground end GND. The voltage limiting sub-circuit 150 is used to limit the voltage input to the driver chip 110.

[0040] For example, if the maximum withstand voltage of the driver chip 110 is 700 V, and the input voltage of the flyback converter 200 is 1500 V, the voltage input to the driver chip is 700 V by setting the voltage limiting subcircuit 150. If the input voltage of the flyback converter 200 is lower than the maximum withstand voltage of the driver chip 110, the voltage input to the driver chip 110 is the input voltage of the flyback converter 200.

[0041] The specific circuit structures of the voltage comparison subcircuit 120, the linear voltage regulation subcircuit 140 and the voltage limiting subcircuit 150 are shown in FIG. Figure 3 Partial detailed explanation.

[0042] Figure 3 is another circuit connection diagram of the undervoltage protection circuit provided in the embodiment of the present application, the voltage dividing module includes but is not limited to resistors, Figure 3 The voltage divider module is shown as a resistor. Figure 3 As shown, the voltage comparison subcircuit 120 may include: a first voltage division module R1, a second voltage division module R2, a first capacitor C1, a comparator U1, a third voltage division module R3, a fourth voltage division module R4, a second capacitor C2, a pull-up resistor R5 and a third capacitor C3.

[0043] The first end of the first voltage divider module R1 is electrically connected to the second end of the linear voltage stabilization sub-circuit 140, the first end of the second voltage divider module R2 is electrically connected to the second end of the first voltage divider module R1, the second end of the second voltage divider module R2 is electrically connected to the ground terminal GND, the first end of the first capacitor C1 is electrically connected to the second end of the first voltage divider module R1 and the first end of the second voltage divider module R2, and the second end of the first capacitor C1 is electrically connected to the ground terminal GND.

[0044] The power supply end of the comparator U1 is electrically connected to the second end of the linear voltage regulator sub-circuit 140, the first input end of the comparator U1 is electrically connected to the second end of the first voltage divider module R1, the first end of the second voltage divider module R2 and the first end of the first capacitor C1, the ground end GND of the comparator U1 is electrically connected to the ground end GND, and the output end of the comparator U1 is electrically connected to the control end of the first switch module 130.

[0045] The first end of the third voltage divider module R3 is electrically connected to the positive voltage input terminal of the flyback converter 200, and the second end of the third voltage divider module R3 is electrically connected to the second input terminal of the comparator U1; the first end of the fourth voltage divider module R4 is electrically connected to the second end of the third voltage divider module R3, and the second end of the fourth voltage divider module R4 is electrically connected to the negative voltage input terminal of the flyback converter 200 and the ground terminal GND.

[0046] A first end of the second capacitor C2 is electrically connected to the second end of the third voltage dividing module R3 and the second input end of the comparator U1 , and a second end of the second capacitor C2 is electrically connected to the ground end GND.

[0047] The first end of the pull-up resistor R5 is electrically connected to the second end of the linear voltage regulator subcircuit 140, and the second end of the pull-up resistor R5 is electrically connected to the control end of the first switch module 130 and the output end of the comparator U1. The first end of the third capacitor C3 is electrically connected to the second end of the pull-up resistor R5, and the second end of the third capacitor C3 is electrically connected to the ground terminal GND.

[0048] It should be understood that the first capacitor C1 acts as a decoupling device to make the input voltage of the non-inverting input terminal of the comparator U1 more stable. The input voltage of the non-inverting input terminal of the comparator U1 (i.e., the reference voltage VREF) is determined by the setting of the linear voltage stabilization sub-circuit 140 and the resistance values ​​of the first voltage divider module R1 and the second voltage divider module R2.

[0049] The second capacitor C2 also functions as a decoupling device to stabilize the input voltage of the negative input terminal of the comparator U2. The input voltage of the negative input terminal of the comparator U1 is determined by the input voltage of the flyback converter and the resistance values ​​of the third voltage divider module R3 and the fourth voltage divider module R4.

[0050] Based on this, it can be known that one of the two input terminals of the comparator U1 can reflect the input voltage of the flyback converter, and the other can set the reference voltage. The voltages at both ends can be compared by the comparator U1, and the first level can be output. When the voltage at the negative input terminal is lower than the reference voltage at the positive input terminal, the comparator U1 is in a high impedance state, the first switch module 130 is driven to conduct through the pull-up resistor R5, the FAULT terminal potential is pulled to the ground, and the driver chip 110 is locked and does not work. When the voltage at the negative input terminal of the comparator U1 is higher than the voltage at the positive input terminal, U1 outputs a low level, the first switch module 130 is turned off, and the driver chip 110 and the power supply work normally.

[0051] By properly designing the output voltage value of the voltage divider modules R1, R2, R3 and R4 and the linear voltage regulator sub-circuit 140, the threshold of the input undervoltage protection can be controlled.

[0052] For the specific structure of the linear voltage regulator subcircuit 140, see Figure 3 ,like Figure 3As shown, the undervoltage protection circuit may further include: a fourth capacitor C4.

[0053] A fourth capacitor C4, a first end of the fourth capacitor C4 is electrically connected to the power input terminal VCC of the driving chip 110, and a second end of the fourth capacitor C4 is electrically connected to the ground terminal GND and the ground terminal GND of the driving chip.

[0054] The linear voltage stabilization sub-circuit 140 may include: a transistor Q2 , a driving resistor R6 , a fifth voltage dividing module R7 , a sixth voltage dividing module R8 , and a first decoupling module C5 .

[0055] The first end of the transistor Q2 is electrically connected to the power input terminal VCC of the driving chip 110; the first end of the driving resistor R6 is electrically connected to the control terminal of the transistor Q2, and the second end of the driving resistor R6 is electrically connected to the first end of the transistor Q2; the first end of the first voltage stabilizing module Z1 is electrically connected to the control terminal of the transistor Q2, and the second end of the first voltage stabilizing module Z1 is electrically connected to the ground terminal GND.

[0056] The first end of the fifth voltage-dividing module R7 is electrically connected to the second end of the transistor Q2, and the second end of the fifth voltage-dividing module R7 is electrically connected to the third end of the first voltage-stabilizing module Z1; the first end of the sixth voltage-dividing module R8 is electrically connected to the second end of the fifth voltage-dividing module R7 and the third end of the first voltage-stabilizing module Z1, and the second end of the sixth voltage-dividing module R8 is electrically connected to the ground terminal GND; the first end of the first decoupling module C5 is electrically connected to the second end of the driving resistor R6, and the second end of the first decoupling module C5 is electrically connected to the ground terminal GND.

[0057] The first voltage stabilizing module Z1 includes but is not limited to a three-terminal adjustable shunt regulator. By way of example, when the voltage of the three-terminal adjustable shunt regulator is 2.5V, the voltage divided by the fifth voltage divider module R7 and the sixth voltage divider module R8 is also not 2.5V. The resistance values ​​of the three-terminal adjustable shunt regulator and the fifth voltage divider module R7 and the sixth voltage divider module R8 are changed to adjust the output voltage of the linear voltage stabilizing sub-circuit 140.

[0058] Continue to see Figure 3 The voltage limiting subcircuit 150 may include: a current limiting module R9, an overvoltage protection module Z2, a second switch module Q3, a seventh voltage dividing module R10, a first reverse cutoff module D1, a second decoupling module C6, an eighth voltage dividing module R11 and a second voltage stabilizing module Z2.

[0059] The first end of the current limiting module R9 is electrically connected to the input end of the flyback converter 200; the first end of the overvoltage protection module Z2 is electrically connected to the second end of the current limiting module R9, and the second end of the overvoltage protection module Z2 is electrically connected to the ground terminal GND; the control end of the second switch module Q3 is electrically connected to the first end of the overvoltage protection module Z2, and the first end of the switch module is electrically connected to the first end of the current limiting module R9; the first end of the seventh voltage dividing module R10 is electrically connected to the second end of the second switch module Q3; the first end of the first reverse cut-off module D1 is electrically connected to the second end of the seventh voltage dividing module R10, and the second end of the first reverse cut-off module D1 is electrically connected to the high voltage input terminal HV of the driving chip 110.

[0060] The first end of the second decoupling module C6 is electrically connected to the first end of the overvoltage protection module Z2 and the control end of the second switch module Q3, and the second end of the second decoupling module C6 is electrically connected to the first end of the seventh voltage dividing module R10; the first end of the eighth voltage dividing module R11 is electrically connected to the first end of the second decoupling module C6, and the second end of the eighth voltage dividing module R11 is electrically connected to the first end of the seventh voltage dividing module R10; the first end of the second voltage stabilizing module Z2 is electrically connected to the first end of the second decoupling module C6, and the second end of the second voltage stabilizing module Z2 is electrically connected to the first end of the seventh voltage dividing module R10.

[0061] in, Figure 3 The overvoltage protection module Z2 in the embodiment is illustrated by taking a transient voltage suppression diode as an example. By selecting parameters of the transient voltage suppression diode, the voltage limiting subcircuit 150 can be clamped at a required voltage.

[0062] Figure 4 is a circuit connection diagram of a flyback power supply circuit provided in an embodiment of the present application, such as Figure 4 As shown, the flyback power supply circuit 300 may include: a flyback converter 200 and an undervoltage protection circuit 100 , and the undervoltage protection circuit 100 is electrically connected to the flyback converter 200 .

[0063] The flyback converter 200 may include: a third switch module Q4 , a first transformer T1 , a fourth switch module Q5 , and a second transformer T2 .

[0064] The control end of the third switch module Q4 is electrically connected to the drive signal output end of the drive chip 110 of the undervoltage protection circuit 100; the first end of the first primary winding of the first transformer T1 is electrically connected to the positive voltage power supply end, the second end of the first primary winding is electrically connected to the first end of the third switch module Q4, and the first secondary winding of the first transformer T1 is electrically connected to the output end.

[0065] The control end of the fourth switch module Q5 is electrically connected to the drive signal output end of the driver chip 110; the first end of the second primary winding of the second transformer T2 is electrically connected to the second end of the third switch module Q4, the second end of the second primary winding is electrically connected to the first end of the fourth switch module Q5, and the second secondary winding of the second transformer T2 is electrically connected to the power input end VCC of the driver chip 110 of the undervoltage protection circuit 100.

[0066] The purpose of the first transformer T1 is to output power, and the purpose of the second transformer T2 is to supply power to the driver chip 110 .

[0067] Continue to see Figure 4 The flyback converter 200 may further include: a second reverse cutoff module D2, a third decoupling module 401, a first sampling module 402, a third reverse cutoff module D3, a fourth decoupling module 403, a second sampling module 404, a fourth reverse cutoff module D4, a fifth decoupling module 405, a fifth reverse cutoff module D5 and a sixth decoupling module 406.

[0068] The first end of the second reverse cutoff module D2 is electrically connected to the first end of the first primary winding, and the second end of the second reverse cutoff module D2 is electrically connected to the positive voltage input end; the first end of the third decoupling module is electrically connected to the second end of the second reverse cutoff module D2 and the positive voltage input end.

[0069] A first end of the first sampling module 402 is electrically connected to a second end of the third switch module Q4, and a second end of the first sampling module 402 is electrically connected to a second end of the third decoupling module; Figure 4 Taking the first sampling module 402 as a current sensor as an example, the first sampling module 402 is used to collect the current of the branch where it is located and send it to the driving chip.

[0070] The first end of the third reverse cutoff module D3 is electrically connected to the first end of the second primary winding, and the second end of the third reverse cutoff module D3 is electrically connected to the second end of the third decoupling module and the high-voltage input terminal HV of the driving chip 110; the first end of the fourth decoupling module 403 is electrically connected to the first end of the second primary winding and the second section of the third decoupling module, and the second end of the fourth decoupling module 403 is electrically connected to the ground terminal GND; the second sampling module 404, the first end of the second sampling module 404 is electrically connected to the second end of the fourth switch module Q5, and the second end of the second sampling module 404 is electrically connected to the ground terminal GND.

[0071] The third decoupling module 401 and the fourth decoupling module 403 may be composed of four capacitors, and the second sampling module includes but is not limited to a resistor R12, such as Figure 4 shown.

[0072] The first end of the fourth reverse cutoff module D4 is electrically connected to the first end of the first secondary winding, and the second end of the fourth reverse cutoff module D4 is electrically connected to the output end; the first end of the fifth decoupling module 405 is electrically connected to the second end of the fourth reverse cutoff module D4, and the second end of the fifth decoupling module 405 is electrically connected to the second end of the first secondary winding. The fifth decoupling module 405 includes but is not limited to capacitor C15. The function of D4 and C15 is to filter out interference and make the output voltage more stable.

[0073] A first end of the fifth reverse cutoff module D5 is electrically connected to a first end of the second secondary winding, and a second end of the fifth reverse cutoff module D5 is electrically connected to a power input terminal VCC of the driving chip 110; a first end of the sixth decoupling module 406 is electrically connected to a second end of the fifth reverse cutoff module D5, and a second end of the sixth decoupling module 406 is electrically connected to a ground terminal GND and a second end of the second secondary winding.

[0074] The sixth decoupling module 406 includes but is not limited to capacitor C16. The function of D5 and C16 is to filter out interference and make the power supply voltage for the driver chip more stable.

[0075] Based on the above analysis, the present application realizes that when the input voltage VBUS+ of the flyback power supply is too small, it is compared with the reference voltage VREF through the voltage comparison sub-circuit 120, and the first level is output to control the first switch module 130 to be turned on, the FAULT terminal of the driver chip 110 is grounded, the driver chip enters a locked state, and the Drive terminal does not send a wave to the third switch module Q4 and the fourth switch module Q5, so that the flyback converter cannot start working, thereby ensuring that the flyback power supply operates within the extreme design conditions and reducing the risk of use.

[0076] It should be understood that the specific structures of the circuits provided in the drawings of the embodiments of the present application are merely examples and are not intended to limit the present application. In addition, the above embodiments provided in the present application may be combined with each other if there is no contradiction.

[0077] It should be clear that each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. According to the embodiments described above in this application, these embodiments do not describe all the details in detail, nor do they limit the application to only the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the application, so that technicians in the relevant technical field can make good use of the application and the modified use based on the application. The application is only limited by the claims and their full scope and equivalents.

[0078] Those skilled in the art should understand that the above embodiments are exemplary rather than restrictive. Different technical features appearing in different embodiments can be combined to achieve beneficial effects. Based on the study of the drawings, the specification and the claims, those skilled in the art should be able to understand and implement other variations of the disclosed embodiments. In the claims, the term "comprising" does not exclude other structures; the quantity involves "one" but does not exclude multiple; the terms "first" and "second" are used to indicate names rather than to indicate any specific order. Any figure marks in the claims should not be understood as limiting the scope of protection. The appearance of certain technical features in different dependent claims does not mean that these technical features cannot be combined to achieve beneficial effects.

Claims

1. An undervoltage protection circuit, characterized in that: include: Driver chip; a voltage comparison subcircuit, wherein a first input terminal of the voltage comparison subcircuit is used to receive a reference voltage, a second input terminal of the voltage comparison subcircuit is electrically connected to an input terminal of the flyback converter, and the voltage comparison subcircuit is used to output a first level in response to an input voltage of the flyback converter being lower than the reference voltage; a first switch module, wherein a control end of the first switch module is electrically connected to an output end of the voltage comparison subcircuit, a first end of the first switch module is electrically connected to a fault feedback end of the driver chip, a second end of the first switch module is electrically connected to a ground end, and the first switch module is used to connect the fault feedback end of the driver chip to the ground end in response to the first level conduction; The driver chip is used to enter a locked state in response to the fault feedback terminal of the driver chip being connected to the ground terminal, so that the drive signal output terminal of the driver chip does not send a drive signal to the flyback converter.

2. The undervoltage protection circuit according to claim 1, characterized in that: The undervoltage protection circuit further includes: A linear voltage stabilization subcircuit, wherein the first end of the linear voltage stabilization subcircuit is electrically connected to the power input end of the driving chip and the chip power supply end of the flyback converter, the second end of the linear voltage stabilization subcircuit is electrically connected to the first input end of the voltage comparison subcircuit, and the linear voltage stabilization subcircuit provides the reference voltage to the voltage comparison subcircuit through the second end.

3. The undervoltage protection circuit according to claim 2, characterized in that: The voltage comparison subcircuit comprises: a first voltage dividing module, wherein a first end of the first voltage dividing module is electrically connected to a second end of the linear voltage stabilizing sub-circuit; a second voltage dividing module, wherein a first end of the second voltage dividing module is electrically connected to a second end of the first voltage dividing module, and a second end of the second voltage dividing module is electrically connected to the ground end; A first capacitor, wherein a first end of the first capacitor is electrically connected to a second end of the first voltage divider module and a first end of the second voltage divider module, and a second end of the first capacitor is electrically connected to a ground end; A comparator, wherein a power supply end of the comparator is electrically connected to the second end of the linear voltage stabilization subcircuit, a first input end of the comparator is electrically connected to the second end of the first voltage divider module, a first end of the second voltage divider module and a first end of the first capacitor, a ground end of the comparator is electrically connected to the ground end, and an output end of the comparator is electrically connected to the control end of the first switch module; a third voltage dividing module, wherein a first end of the third voltage dividing module is electrically connected to the positive voltage input end of the flyback converter, and a second end of the third voltage dividing module is electrically connected to the second input end of the comparator; a fourth voltage-dividing module, wherein a first end of the fourth voltage-dividing module is electrically connected to a second end of the third voltage-dividing module, and a second end of the fourth voltage-dividing module is electrically connected to a negative voltage input end and a ground end of the flyback converter; a second capacitor, wherein a first end of the second capacitor is electrically connected to the second end of the third voltage divider module and the second input end of the comparator, and a second end of the second capacitor is electrically connected to the ground end; A pull-up resistor, wherein a first end of the pull-up resistor is electrically connected to a second end of the linear voltage stabilization subcircuit, and a second end of the pull-up resistor is electrically connected to a control end of the first switch module and an output end of the comparator; A third capacitor, wherein a first end of the third capacitor is electrically connected to the second end of the pull-up resistor, and a second end of the third capacitor is electrically connected to the ground end.

4. The undervoltage protection circuit according to claim 2, characterized in that: The linear voltage stabilization subcircuit comprises: A transistor, wherein a first end of the transistor is electrically connected to a power input end of the driving chip; a driving resistor, wherein a first end of the driving resistor is electrically connected to the control end of the transistor, and a second end of the driving resistor is electrically connected to the first end of the transistor; A first voltage stabilizing module, wherein a first end of the first voltage stabilizing module is electrically connected to the control end of the transistor, and a second end of the first voltage stabilizing module is electrically connected to the ground end; a fifth voltage-dividing module, wherein a first end of the fifth voltage-dividing module is electrically connected to a second end of the transistor, and a second end of the fifth voltage-dividing module is electrically connected to a third end of the first voltage-stabilizing module; a sixth voltage-dividing module, wherein a first end of the sixth voltage-dividing module is electrically connected to a second end of the fifth voltage-dividing module and a third end of the first voltage-stabilizing module, and a second end of the sixth voltage-dividing module is electrically connected to a ground end; A first decoupling module, wherein a first end of the first decoupling module is electrically connected to a second end of the driving resistor, and a second end of the first decoupling module is electrically connected to a ground end.

5. The undervoltage protection circuit according to claim 1, characterized in that: The undervoltage protection circuit further includes: a voltage limiting subcircuit, wherein a first end of the voltage limiting subcircuit is electrically connected to an input end of the flyback converter, a second end of the voltage limiting subcircuit is electrically connected to a high voltage input end of the driver chip, a third end of the voltage limiting subcircuit is electrically connected to a ground end, and the voltage limiting subcircuit is used to limit a voltage input to the driver chip; A fourth capacitor, wherein a first end of the fourth capacitor is electrically connected to the power input end of the driving chip, and a second end of the fourth capacitor is electrically connected to the ground end and the ground end of the driving chip.

6. The undervoltage protection circuit according to claim 5, characterized in that: The voltage limiting subcircuit comprises: A current limiting module, a first end of which is electrically connected to an input end of the flyback converter; An overvoltage protection module, wherein a first end of the overvoltage protection module is electrically connected to a second end of the current limiting module, and a second end of the overvoltage protection module is electrically connected to a ground end; A second switch module, wherein a control end of the second switch module is electrically connected to a first end of the overvoltage protection module, and a first end of the switch module is electrically connected to a first end of the current limiting module; a seventh voltage dividing module, wherein a first end of the seventh voltage dividing module is electrically connected to a second end of the second switch module; A first reverse cutoff module, wherein a first end of the first reverse cutoff module is electrically connected to a second end of the seventh voltage dividing module, and a second end of the first reverse cutoff module is electrically connected to a high voltage input end of the driving chip.

7. The undervoltage protection circuit according to claim 6, characterized in that: The voltage limiting subcircuit also includes: a second decoupling module, wherein a first end of the second decoupling module is electrically connected to a first end of the overvoltage protection module and a control end of the second switch module, and a second end of the second decoupling module is electrically connected to a first end of the seventh voltage dividing module; an eighth voltage dividing module, wherein a first end of the eighth voltage dividing module is electrically connected to a first end of the second decoupling module, and a second end of the eighth voltage dividing module is electrically connected to a first end of the seventh voltage dividing module; A second voltage stabilizing module, wherein a first end of the second voltage stabilizing module is electrically connected to a first end of the second decoupling module, and a second end of the second voltage stabilizing module is electrically connected to a first end of the seventh voltage dividing module.

8. A flyback power supply circuit, characterized in that: include: Flyback converter; The undervoltage protection circuit according to any one of claims 1 to 7, wherein the undervoltage protection circuit is electrically connected to the flyback converter.

9. The flyback power supply circuit according to claim 8, characterized in that: The flyback converter comprises: A third switch module, wherein a control end of the third switch module is electrically connected to a drive signal output end of a drive chip of the undervoltage protection circuit; a first transformer, wherein a first end of a first primary winding of the first transformer is electrically connected to a positive voltage power supply end, a second end of the first primary winding is electrically connected to a first end of the third switch module, and a first secondary winding of the first transformer is electrically connected to an output end; a fourth switch module, wherein a control end of the fourth switch module is electrically connected to a drive signal output end of the drive chip; A second transformer, a first end of a second primary winding of the second transformer is electrically connected to a second end of the third switch module, a second end of the second primary winding is electrically connected to a first end of the fourth switch module, and a second secondary winding of the second transformer is electrically connected to a power input end of a driving chip of the undervoltage protection circuit.

10. The flyback power supply circuit according to claim 9, characterized in that: The flyback power supply circuit also includes: a second reverse cutoff module, wherein a first end of the second reverse cutoff module is electrically connected to a first end of the first primary winding, and a second end of the second reverse cutoff module is electrically connected to the positive voltage input end; a third decoupling module, wherein a first end of the third decoupling module is electrically connected to a second end of the second reverse cutoff module and the positive voltage input end; a first sampling module, wherein a first end of the first sampling module is electrically connected to a second end of the third switch module, and a second end of the first sampling module is electrically connected to a second end of the third decoupling module; a third reverse cutoff module, wherein a first end of the third reverse cutoff module is electrically connected to a first end of the second primary winding, and a second end of the third reverse cutoff module is electrically connected to a second end of the third decoupling module and a high voltage input end of the driving chip; a fourth decoupling module, wherein a first end of the fourth decoupling module is electrically connected to the first end of the second primary winding and the second section of the third decoupling module, and a second end of the fourth decoupling module is electrically connected to a ground end; a second sampling module, wherein a first end of the second sampling module is electrically connected to a second end of the fourth switch module, and a second end of the second sampling module is electrically connected to a ground end; a fourth reverse cutoff module, wherein a first end of the fourth reverse cutoff module is electrically connected to a first end of the first secondary winding, and a second end of the fourth reverse cutoff module is electrically connected to an output end; a fifth decoupling module, wherein a first end of the fifth decoupling module is electrically connected to a second end of the fourth reverse cutoff module, and a second end of the fifth decoupling module is electrically connected to a second end of the first secondary winding; a fifth reverse cutoff module, wherein a first end of the fifth reverse cutoff module is electrically connected to a first end of the second secondary winding, and a second end of the fifth reverse cutoff module is electrically connected to a power input end of the driving chip; A sixth decoupling module, wherein a first end of the sixth decoupling module is electrically connected to a second end of the fifth reverse cutoff module, and a second end of the sixth decoupling module is electrically connected to a ground end and a second end of the second secondary winding.

Images