Undervoltage protection circuit for a quasi-resonant flyback chip
By introducing an overvoltage lockout circuit into the undervoltage circuit of the quasi-resonant flyback chip, including components such as chip U1, transistors Q1 and Q2, and optocoupler OT1, the problem of insufficient overvoltage protection is solved, realizing the self-locking function of the equipment and protection under overvoltage conditions, preventing equipment damage and the spread of faults.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- CHANGZHOU CHENGLIAN POWER SUPPLY MFG
- Filing Date
- 2025-07-21
- Publication Date
- 2026-07-03
AI Technical Summary
Existing quasi-resonant flyback chip undervoltage protection circuits cannot effectively protect circuits from overvoltage damage, leading to equipment damage, insulation breakdown, and fire risks. Furthermore, they lack self-locking functionality to prevent the fault from escalating.
An overvoltage lockout circuit is set on the undervoltage circuit, including components such as chip U1, transistors Q1 and Q2, and optocoupler OT1, to achieve a self-locking function. When overvoltage occurs, the circuit locks up to prevent the fault from spreading. Through the cooperation of operational amplifiers U2 and U3, it is ensured that the circuit stops working under overvoltage conditions.
It effectively prevents equipment damage, avoids insulation breakdown and fire risks, protects batteries and power modules, prevents data loss and equipment failure, and implements a self-locking function to prevent the fault from escalating.
Smart Images
Figure CN224459234U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to an undervoltage protection circuit, and more particularly to an undervoltage protection circuit for a quasi-resonant flyback chip, belonging to the field of protection circuit technology. Background Technology
[0002] Quasi-resonant flyback chips are semiconductor devices widely used in power management. They combine quasi-resonant technology and the principle of flyback switching power supplies to achieve efficient and compact power conversion. Quasi-resonant flyback chips incorporate an undervoltage circuit, which primarily detects whether the power supply voltage is lower than a predetermined safe operating voltage. When the voltage falls below this threshold, the undervoltage circuit takes measures such as issuing a warning or triggering protective measures to prevent the device from operating under low voltage conditions, thereby avoiding potential damage or performance degradation. However, relying solely on the undervoltage circuit is insufficient to completely protect the circuit from all voltage anomalies, especially overvoltage conditions. When the power supply voltage exceeds a predetermined maximum value, the overvoltage protection circuit will quickly take measures such as disconnecting the power supply or reducing the voltage of the controlled device to prevent electronic equipment and components from being damaged or burned out due to overheating.
[0003] Therefore, it is urgent to improve the undervoltage protection circuit of the quasi-resonant flyback chip to solve the above-mentioned problems. Utility Model Content
[0004] The purpose of this invention is to provide an undervoltage protection circuit for a quasi-resonant flyback chip. Setting an overvoltage lockout circuit on the undervoltage circuit is of great significance for protecting the circuit and its connected electronic equipment from damage caused by excessive voltage. It not only helps to prevent equipment damage, avoid insulation breakdown and fire risks, but also protects the battery and power module, prevents data loss and equipment failure, and realizes a self-locking function to prevent the fault from escalating.
[0005] To achieve the above objectives, the main technical solutions adopted by this utility model include:
[0006] An undervoltage protection circuit for a quasi-resonant flyback chip includes an undervoltage circuit, an overvoltage lockout circuit electrically connected to the input terminal of the undervoltage circuit, an output terminal of the overvoltage lockout circuit electrically connected to the +Vin terminal of the undervoltage circuit, and a Vcc terminal of the overvoltage lockout circuit electrically connected to the undervoltage circuit.
[0007] The overvoltage lockout circuit includes a chip U1, on which transistors Q1 and Q2 are connected in parallel. An optocoupler OT1 is electrically connected between transistors Q1 and Q2, and one end of the optocoupler OT1 is connected to a power supply.
[0008] The undervoltage circuit includes operational amplifiers U2 and U3, with diodes D1, D2, and D3 electrically connected to operational amplifiers U2 and U3. Diode D1 is electrically connected to CNT, and diode D2 is connected to the overvoltage lockout circuit through resistor Rc2.
[0009] Preferably, the transistor Q1 is electrically connected to the chip U1, the chip U1 is model UC3842, a resistor R12 is electrically connected to pin 1 of the transistor Q1, and a resistor R13 is electrically connected to the transistor Q2 on pin 2 of the transistor Q1.
[0010] Preferably, the transistor Q2 is electrically connected to the chip U1 through resistor R14, and is also electrically connected to the optocoupler OT1;
[0011] Resistors R16 and R15 are electrically connected to pin 2 of transistor Q2. The overvoltage lockout circuit is electrically connected to the undervoltage circuit through resistor R19 and diode D4.
[0012] Preferably, the +Vin terminal of the overvoltage lockout circuit is electrically connected to the operational amplifier U3, and resistors R2 and R3 are electrically connected between the overvoltage lockout circuit and the operational amplifier U3, and the transistor Q2 is electrically connected to the operational amplifier U2.
[0013] Preferably, resistors R8 and R7 are connected in parallel on pin 3 of the operational amplifier U3, and resistor R8 is connected in parallel with diode D3;
[0014] A resistor R11 and a resistor R11A are electrically connected to pin 3 of the diode D3, and a transistor Q3 is electrically connected between the resistor R11 and the resistor R11A.
[0015] Preferably, pin 2 of the operational amplifier U3 is electrically connected to the diode D1, and a resistor Rt 1 and a resistor Q5A are connected in parallel on pin 2 of the operational amplifier U3. The resistor Rt 1 is electrically connected to pin 5 of the operational amplifier U3.
[0016] Preferably, pin 3 of diode D2 is electrically connected to pin 7 of operational amplifier U2, and a resistor R10 is electrically connected between diode D2 and operational amplifier U2.
[0017] This utility model has at least the following beneficial effects:
[0018] 1. When the output voltage increases, diode D4 conducts, optocoupler OT1 conducts, and the base of transistor Q2 is energized and conducts. Due to the conduction of transistor Q2, the base voltage of transistor Q1 decreases and it also conducts. The Vcc voltage, through resistor R17, transistor Q1, and resistor R16, keeps transistor Q2 conducting. Chip U1 remains at a high level and stops working. Setting up an overvoltage lockout circuit on the undervoltage circuit is of great significance for protecting the circuit and its connected electronic equipment from damage caused by excessive voltage. It not only helps prevent equipment damage, avoids insulation breakdown and fire risks, but also protects the battery and power module, prevents data loss and equipment failure, and achieves a self-locking function to prevent the fault from escalating.
[0019] 2. When module CNT is in negative logic, diode D1 and resistor Rc2 are connected to CNT at a low level when the module is working normally. At this time, the operational amplifier U2 outputs a low level, which reduces the input voltage. When the voltage on pin 2 of operational amplifier U3 is lower than the voltage on pin 3, operational amplifier U3 outputs a high level, which turns on transistor Q3 and pulls pin 1 low, turning off the module. At this time, the voltage on pin 1 of operational amplifier U3 is approximately equal to Vcc, which causes the potential on pin 3 of operational amplifier U3 to rise. Therefore, when the undervoltage recovery point is higher than the undervoltage point, hysteresis is generated. Attached Figure Description
[0020] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:
[0021] Figure 1 This is the circuit diagram of this utility model.
[0022] In the diagram, 1 is the undervoltage circuit; 2 is the overvoltage lockout circuit. Detailed Implementation
[0023] The following will describe in detail the implementation of this application with reference to the accompanying drawings and embodiments, so that the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.
[0024] like Figure 1As shown, the undervoltage protection circuit of the quasi-resonant flyback chip provided in this embodiment includes an undervoltage circuit 1. An overvoltage lockout circuit 2 is electrically connected to the input terminal of the undervoltage circuit 1. The output terminal of the overvoltage lockout circuit 2 is electrically connected to the +Vin terminal of the undervoltage circuit 1. The Vcc terminal of the overvoltage lockout circuit 2 is electrically connected to the undervoltage circuit 1. The undervoltage circuit is mainly used to detect whether the power supply voltage is lower than the predetermined safe operating voltage. When the voltage is lower than this threshold, the undervoltage circuit will take measures, such as issuing a warning or triggering protection measures, to prevent the equipment from working under low voltage conditions, thereby avoiding possible damage or performance degradation. However, relying solely on the undervoltage circuit is not enough to completely protect the circuit from all voltage anomalies, especially overvoltage conditions. When the power supply voltage exceeds the predetermined maximum value, the overvoltage protection circuit will quickly take measures, such as disconnecting the power supply or reducing the voltage of the controlled equipment, to prevent electronic equipment and components from being damaged or burned due to overheating.
[0025] The overvoltage lockout circuit 2 set on the undervoltage circuit 1 includes a self-locking function. Once an overvoltage occurs, the circuit will "lock" and can only be unlocked after the fault is cleared or power is restored. This design can effectively prevent the expansion of the fault surface and better protect the device and the load.
[0026] The overvoltage lockout circuit 2 includes a chip U1. Transistors Q1 and Q2 are connected in parallel on chip U1. An optocoupler OT1 is electrically connected between transistors Q1 and Q2, with one end of OT1 connected to the power supply. Transistor Q1 is electrically connected to chip U1 (model: UC3842). A resistor R12 is electrically connected to pin 1 of transistor Q1. A resistor R13 connects pin 2 of transistor Q1 to transistor Q2. Transistor Q2 is electrically connected to chip U1 via resistor R14 and also to optocoupler OT1. Resistors R16 and R15 are electrically connected to pin 2 of transistor Q2. The overvoltage lockout circuit 2 is connected via resistor R19 and a diode. D4 is electrically connected to the undervoltage circuit 1. When the output voltage increases, diode D4 conducts, optocoupler OT1 conducts, and the base of transistor Q2 is energized and conducts. Due to the conduction of transistor Q2, the base voltage of transistor Q1 decreases and it also conducts. The Vcc voltage, through resistor R17, transistor Q1, and resistor R16, keeps transistor Q2 conducting. Chip U1 is always at a high level and stops working. Setting up an overvoltage lockout circuit 2 on the undervoltage circuit 1 is of great significance for protecting the circuit and its connected electronic equipment from damage caused by excessive voltage. It not only helps to prevent equipment damage, avoid insulation breakdown and fire risks, but also protects the battery and power module, prevents data loss and equipment failure, and realizes a self-locking function to prevent the fault from spreading.
[0027] Furthermore, such as Figure 1As shown, the undervoltage circuit 1 includes operational amplifiers U2 and U3. Diodes D1, D2, and D3 are electrically connected to operational amplifiers U2 and U3. Diode D2 is electrically connected to overvoltage lockout circuit 2 through resistor Rc2. The +Vin terminal of overvoltage lockout circuit 2 is electrically connected to operational amplifier U3. Resistors R2 and R3 are electrically connected between overvoltage lockout circuit 2 and operational amplifier U3. Transistor Q2 is electrically connected to operational amplifier U2. A CNT is electrically connected to diode D1. Resistors R8 and R7 are connected in parallel on pin 3 of operational amplifier U3. Resistor R8 is connected in parallel with diode D3.
[0028] Resistors R11 and R11A are electrically connected to pin 3 of diode D3. Transistor Q3 is electrically connected between resistors R11 and R11A. When module CNT is in negative logic, diode D1 and resistor Rc2 are connected to CNT at a low level when the module is working normally. At this time, the operational amplifier U2 outputs a low level, which reduces the input voltage. When the voltage on pin 2 of operational amplifier U3 is lower than the voltage on pin 3, operational amplifier U3 outputs a high level, which turns on transistor Q3 and pulls pin 1 low, turning off the module. At this time, the voltage on pin 1 of operational amplifier U3 is approximately equal to Vcc, which causes the potential on pin 3 of operational amplifier U3 to rise. Therefore, when the undervoltage recovery point is higher than the undervoltage point, hysteresis is generated.
[0029] Furthermore, such as Figure 1 As shown, pin 2 of operational amplifier U3 is electrically connected to diode D1. Resistors Rt1 and Q5A are connected in parallel on pin 2 of operational amplifier U3. Resistor Rt1 is electrically connected to pin 5 of operational amplifier U.
[0030] In this embodiment, as Figure 1 As shown, pin 3 of diode D2 is electrically connected to pin 7 of operational amplifier U2, and a resistor R10 is electrically connected between diode D2 and operational amplifier U2. As the circuit board temperature rises, the resistance of resistor RT1 decreases, and the potential on pin 5 of operational amplifier U2 gradually rises. When the temperature of the aluminum substrate reaches the over-temperature protection point, the potential on pin 5 of operational amplifier U2 is higher than the potential on pin 6, and operational amplifier U2 outputs a high level, thereby turning on transistor Q3, pulling pin 1 low, and turning off the module. Similarly, the over-temperature protection will also produce hysteresis.
[0031] like Figure 1 As shown, the principle of the undervoltage protection circuit of the quasi-resonant flyback chip provided in this embodiment is as follows:
[0032] The input terminal of the undervoltage circuit 1 is electrically connected to the overvoltage lockout circuit 2. The undervoltage circuit is mainly used to detect whether the power supply voltage is lower than the predetermined safe operating voltage. When the voltage is lower than this threshold, the undervoltage circuit will take measures, such as issuing a warning or triggering protection measures, to prevent the equipment from working under low voltage conditions, thereby avoiding possible damage or performance degradation. However, relying solely on the undervoltage circuit is not enough to completely protect the circuit from all voltage anomalies, especially overvoltage conditions. When the power supply voltage exceeds the predetermined maximum value, the overvoltage protection circuit will quickly take measures, such as disconnecting the power supply or reducing the voltage of the controlled equipment, to prevent electronic equipment and components from being damaged or burned due to overheating.
[0033] The overvoltage lockout circuit 2 set on the undervoltage circuit 1 includes a self-locking function. Once an overvoltage occurs, the circuit will "lock" and can only be unlocked after the fault is cleared or power is restored. This design can effectively prevent the expansion of the fault surface and better protect the device and the load.
[0034] When the output voltage increases, diode D4 conducts, optocoupler OT1 conducts, and the base of transistor Q2 is energized and conducts. Due to the conduction of transistor Q2, the base voltage of transistor Q1 decreases and it also conducts. The Vcc voltage, through resistor R17, transistor Q1, and resistor R16, keeps transistor Q2 conducting. Chip U1 remains at a high level and stops working. Setting up an overvoltage lockout circuit 2 on the undervoltage circuit 1 is of great significance for protecting the circuit and its connected electronic equipment from damage caused by excessive voltage. It not only helps prevent equipment damage, avoids insulation breakdown and fire risks, but also protects the battery and power module, prevents data loss and equipment failure, and realizes a self-locking function to prevent the fault from spreading.
[0035] If certain terms are used in the specification and claims to refer to specific components, those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The term "comprising" as used throughout the specification and claims is an open-ended term and should be interpreted as "comprising but not limited to." "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error.
[0036] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes that element.
[0037] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.
Claims
1. An undervoltage protection circuit for a quasi-resonant flyback chip, comprising an undervoltage circuit (1), characterized in that, The input terminal of the undervoltage circuit (1) is electrically connected to the overvoltage lockout circuit (2), the output terminal of the overvoltage lockout circuit (2) is electrically connected to the +Vin terminal of the undervoltage circuit (1), and the Vcc terminal of the overvoltage lockout circuit (2) is electrically connected to the undervoltage circuit (1). The overvoltage lockout circuit (2) includes a chip U1, on which transistors Q1 and Q2 are connected in parallel. An optocoupler OT1 is electrically connected between transistors Q1 and Q2, and one end of the optocoupler OT1 is connected to a power supply. The undervoltage circuit (1) includes operational amplifiers U2 and U3, with diodes D1, D2 and D3 electrically connected to operational amplifiers U2 and U3. Diode D1 is electrically connected to CNT, and diode D2 is connected to the overvoltage lockout circuit (2) through resistor Rc2.
2. The undervoltage protection circuit for a quasi-resonant flyback chip according to claim 1, characterized in that: The transistor Q1 is electrically connected to the chip U1, and the chip U1 is model UC3842. A resistor R12 is electrically connected to pin 1 of the transistor Q1, and a resistor R13 is electrically connected to the transistor Q2 on pin 2 of the transistor Q1.
3. The undervoltage protection circuit for a quasi-resonant flyback chip according to claim 1, characterized in that: The transistor Q2 is electrically connected to the chip U1 through resistor R14, and is also electrically connected to the optocoupler OT1; The transistor Q2 has resistors R16 and R15 electrically connected to pin 2. The overvoltage lockout circuit (2) is electrically connected to the undervoltage circuit (1) through resistor R19 and diode D4.
4. The undervoltage protection circuit for a quasi-resonant flyback chip according to claim 1, characterized in that: The +Vin terminal of the overvoltage lockout circuit (2) is electrically connected to the operational amplifier U3, and resistors R2 and R3 are electrically connected between the overvoltage lockout circuit (2) and the operational amplifier U3. The transistor Q2 is electrically connected to the operational amplifier U2.
5. The undervoltage protection circuit for a quasi-resonant flyback chip according to claim 1, characterized in that: Resistors R8 and R7 are connected in parallel on pin 3 of the operational amplifier U3, and resistor R8 is connected in parallel with diode D3. A resistor R11 and a resistor R11A are electrically connected to pin 3 of the diode D3, and a transistor Q3 is electrically connected between the resistor R11 and the resistor R11A.
6. The undervoltage protection circuit for a quasi-resonant flyback chip according to claim 1, characterized in that: Pin 2 of the operational amplifier U3 is electrically connected to the diode D1. A resistor Rt 1 and a resistor Q5A are connected in parallel on pin 2 of the operational amplifier U3. The resistor Rt 1 is electrically connected to pin 5 of the operational amplifier U3.
7. The undervoltage protection circuit for a quasi-resonant flyback chip according to claim 1, characterized in that: Pin 3 of the diode D2 is electrically connected to pin 7 of the operational amplifier U2, and a resistor R10 is electrically connected between the diode D2 and the operational amplifier U2.