Quick reset circuit capable of preventing impact of input surge current

Abstract

The invention relates to an input anti-surge current impact rapid reset circuit, which comprises a charging switch circuit, an input sampling comparison circuit, an isolation anti-reverse circuit and a rapid discharging reset circuit, and is characterized in that the input sampling comparison circuit and the isolation anti-reverse circuit are respectively connected with the charging switch circuit; the isolation anti-reverse circuit electrically isolates a sampling point of the input sampling comparison circuit from a sampling point of the rapid discharge reset circuit, sets a working point of the rapid discharge reset circuit through element parameters of the input sampling circuit, and when the input sampling comparison circuit is powered off at the input moment and the comparison voltage is lower than the internal reference voltage of the rapid discharge reset circuit, the rapid discharge reset circuit is powered off. And the rapid discharge reset circuit starts to work, a power MOS tube of the charging switch circuit is cut off, and rapid reset discharge is realized. According to the invention, the reliability and anti-surge capability of the switching power supply under the transient working condition are obviously improved.

Description

A fast reset circuit for input surge current protection Technical Field

[0001] This invention relates to the field of power supply technology, and in particular to an input surge current protection and fast reset circuit. Background Technology

[0002] In switching power supply systems, the input circuit typically employs AC rectification and filtering or DC with added filter capacitors. At the instant the power is switched on, the initial voltage of the filter capacitor is zero, effectively creating a short circuit and generating a significant inrush current. For high-power switching power supplies, the input filter capacitance is large, often using multiple capacitors connected in parallel, resulting in a lower equivalent resistance and consequently, an even larger inrush current. This transient inrush current can severely damage power devices, reducing the reliability of the power module. Especially in high-power-density designs, large current surges can also cause thermal and electrical stresses in power devices, further increasing the risk of circuit failure. Therefore, effectively suppressing the inrush current during power-on is a key technical challenge for improving power system reliability and extending its lifespan.

[0003] For airborne electrical equipment, there are strict technical requirements for its power supply characteristics. According to national military standards, for electrical equipment with a power greater than 200W (excluding incandescent lamps), when a rated voltage is suddenly applied, the peak inrush current must not exceed five times the rated current, and must drop back to the rated current level within 0.1 seconds. This requirement imposes stringent technical specifications on the surge resistance of airborne power systems. To meet these requirements, almost all airborne electrical equipment is designed with surge protection circuits in its input circuits to ensure that the power system can still operate normally and reliably under extreme conditions. These surge protection circuits typically use MOSFET power transistors connected in parallel with current-limiting resistors to effectively suppress the inrush current by dynamically adjusting the input current.

[0004] In existing surge protection circuit designs, the sampling point of the MOSFET power transistor gate-source charging circuit is typically set at the positive terminal of the main input circuit, as shown in Figure 1. However, due to the presence of a large-capacity filter capacitor in the main input circuit, the drive voltage of the MOSFET power transistor gate-source charging circuit cannot achieve effective and rapid reset after the input power supply is turned off. Especially when using SiC (silicon carbide) devices, their gate-source voltage start-up threshold is low, and they may still conduct even below 3V. This results in the gate-source voltage failing to return to zero during a second rapid power-up, thus failing to effectively achieve surge protection. In this case, the inrush current at the moment of power-up can easily damage the power transistor, causing the power module to malfunction. Furthermore, although some circuit designs employ a detection, comparison, and reset circuit, they do not use isolation diodes or effectively isolate the detection circuit from the reset circuit. As a result, during rapid power-up and power-down, the action speed of the detection circuit is limited by the capacitance at the power input terminal and the load conditions at the power supply downstream, failing to achieve the ideal rapid reset effect. These problems severely restrict the application effect of existing surge protection circuits in high-reliability power supply systems. Summary of the Invention

[0005] To address the existing technical problems, this invention provides an input surge current protection and fast reset circuit.

[0006] The specific content of this invention is as follows: An input surge current protection fast reset circuit includes a charging switch circuit, an input sampling comparison circuit, an isolation anti-reverse circuit, and a fast discharge reset circuit. The input sampling comparison circuit and the isolation anti-reverse circuit are respectively connected to the charging switch circuit. The isolation anti-reverse circuit electrically isolates the sampling point of the input sampling comparison circuit from the sampling point of the fast discharge reset circuit. The operating point of the fast discharge reset circuit is set by the component parameters of the input sampling circuit. When the input is powered down at the moment of input, if the comparison voltage of the input sampling comparison circuit is lower than its internal reference voltage, the fast discharge reset circuit starts to work, and the power MOSFET of the charging switch circuit is turned off, thereby realizing fast reset discharge.

[0007] Furthermore, the charging switch circuit includes drive resistors R1 to R5, delay capacitor C1, protection Zener diode V1, power switching transistor V2, surge current limiting charging resistor R6, and filter capacitor C2. Specifically: one end of resistor R1 is connected to the overcurrent power supply input Vin+; the other end of resistor R1 is connected to one end of resistor R2; the other end of resistor R2 is connected to one end of resistor R3; the other end of resistor R3 is connected to one end of resistor R4; the other end of resistor R4 is connected to one end of capacitor C1, one end of resistor R5, the cathode of Zener diode V1, and the gate of power MOSFET V2; the other end of resistor R5 is connected to the power supply input Vin-, the other end of capacitor C1, the anode of Zener diode V1, the anode of Zener diode V1, one end of resistor R6, and the source of power MOSFET V1; the other end of power resistor R6 is connected to the drain of power MOSFET V3, the negative terminal of the DC / DC converter power supply, and the negative terminal of filter capacitor C2; the positive terminal of filter capacitor C2 is connected to the positive terminal of the DC / DC converter power supply.

[0008] Furthermore, the input sampling and comparison circuit includes sampling resistors R7 to R10, anti-interference capacitor C3, sampling voltage comparator N1, and protection Zener diode V4. Specifically: one end of resistor R7 is connected to the positive terminal of the power supply input Vin; the other end of resistor R7 is connected to one end of resistor R8; the other end of resistor R8 is connected to one end of resistor R9; the other end of resistor R9 is connected to one end of resistor R10, one end of capacitor C3, and the reference voltage terminal of voltage comparator N1; the other end of resistor R10 is connected to the other end of capacitor C3, the anode of voltage comparator N1, and the anode of Zener diode V4; and the cathode of voltage comparator N1 is connected to the cathode of Zener diode V4.

[0009] Furthermore, the isolation and anti-reverse circuit includes an isolation power diode V3, wherein: the anode of diode V3 is connected to the power supply input Vin+, one end of resistor R1, and one end of resistor R7 respectively; the cathode of diode V3 is connected to the positive terminal of filter capacitor C2 and the positive terminal of DC / DC converter power supply respectively.

[0010] Furthermore, the fast discharge reset circuit includes current-limiting resistors R11 to R14, matching diode V5, and discharge optocoupler N2, wherein: one end of resistor R11 is connected to the cathode of the anti-reverse diode; the other end of resistor R11 is connected to one end of resistor R12; the other end of resistor R12 is connected to one end of resistor R13; the other end of resistor R13 is connected to one end of resistor R14, the cathode of voltage comparator N1, and the cathode of protection Zener diode V4; the other end of resistor R14 is connected to the anode of configuration diode V5; the cathode of configuration diode V5 is connected to the anode of the primary diode of optocoupler N2; the cathode of the primary diode of optocoupler N2 is connected to the other end of resistor R10, the other end of capacitor C3, the anode of voltage comparator N1, and the anode of Zener diode; the collector of the secondary transistor of optocoupler N2 is connected to the emitter of power MOSFET V2; and the emitter of the secondary transistor of optocoupler N2 is connected to the source of power MOSFET V2.

[0011] When the input power supply is off, the voltage sampling and comparison circuit of this invention can respond quickly and trigger a fast discharge mechanism. Simultaneously, by utilizing the energy storage characteristics of the large input capacitor, the fast discharge circuit ensures continued operation after power failure, thereby achieving rapid reset of the MOSFET gate-source voltage. During secondary fast power-on, the circuit can fully execute the surge protection charging process, ensuring that the surge protection mechanism remains effective at all times, thus significantly improving the reliability and surge resistance of the switching power supply under transient conditions. Attached Figure Description

[0012] The invention will be further explained below with reference to the accompanying drawings.

[0013] Figure 1 shows a traditional surge protection circuit diagram;

[0014] Figure 2 is a schematic diagram of the input surge current protection fast reset circuit of the present invention. Detailed Implementation

[0015] Referring to Figure 2, this invention provides an input surge current protection fast reset circuit, including a charging switch circuit, an input sampling comparator circuit, an isolation anti-reverse circuit, and a fast discharge reset circuit. This invention proposes an innovative input surge current protection fast reset circuit. By adding an input anti-reverse diode and electrically isolating the input voltage sampling comparator circuit and the fast discharge circuit, it ensures that the voltage sampling comparator circuit can respond quickly after the input power supply is turned off. Simultaneously, utilizing the energy storage characteristics of the large input capacitor, the fast discharge circuit can continue to operate after power failure, thereby achieving rapid reset of the MOSFET gate-source voltage. During secondary rapid power-on, this circuit can fully execute the surge protection charging process, ensuring that the surge protection mechanism is always effective.

[0016] Specifically, this invention adds a reverse polarity protection diode V3 to the circuit, separating the sampling point of the MOSFET gate-source charging circuit from the main power charging circuit, and effectively isolating the input voltage detection sampling point from the sampling point of the fast discharge reset circuit. For different input voltage ranges, the operating point of the fast discharge reset is set by adjusting the parameters of the sampling resistors R7-R10 and utilizing the conduction threshold of the N1 integrated circuit (e.g., 431). When the input power is turned off, the input voltage drops rapidly due to the isolation effect of the input diode, the gate-source charging circuit discharges quickly, and the voltage at the input voltage detection terminal drops rapidly. When the preset fast discharge voltage operating point is reached, the integrated circuit N1 (431) is turned off and does not work. At this time, the voltage drop at the fast discharge sampling terminal is relatively slow due to the presence of input capacitors C2 and C3, providing continuous working energy for the fast discharge circuit. This causes the optocoupler N2 to conduct, and its secondary transistor short-circuits the gate-source drive voltage Vgs of the surge protection circuit, forming a fast discharge circuit and resetting the drive voltage to zero, thus preparing for the next fast power-on. This improved design effectively solves the technical challenges of surge protection circuits during frequent power-on and power-off processes. Especially in power characteristic tests, such as the 50ms power supply switching test, this circuit can effectively ensure the normal operation of the surge protection mechanism, significantly improving the reliability and anti-interference capability of the power system.

[0017] The specific components of this invention are as follows:

[0018] The charging switch circuit includes drive resistors R1 to R5, delay capacitor C1, protection Zener diode V1, power switching transistor V2, surge current limiting charging resistor R6, and filter capacitor C2. Specifically: one end of resistor R1 is connected to the overcurrent power supply input Vin+; the other end of resistor R1 is connected to one end of resistor R2; the other end of resistor R2 is connected to one end of resistor R3; the other end of resistor R3 is connected to one end of resistor R4; the other end of resistor R4 is connected to one end of capacitor C1, one end of resistor R5, the cathode of Zener diode V1, and the gate (G) terminal of power MOSFET V2; the other end of resistor R5 is connected to the power supply input Vin-, the other end of capacitor C1, the anode of Zener diode V1, the anode of Zener diode V1, one end of resistor R6, and the source (S) terminal of power MOSFET V1; the other end of power resistor R6 is connected to the drain (D) terminal of power MOSFET V3, the negative terminal of the DC / DC converter power supply, and the negative terminal of filter capacitor C2; the positive terminal of filter capacitor C2 is connected to the positive terminal of the DC / DC converter power supply.

[0019] At the moment of power-on, the power MOSFET V1 is not turned on in the surge current protection circuit. The 270V power supply input charges the input filter capacitor C2 of the DC / DC converter through the power resistor R6. The surge current is limited by the resistor R6. In this embodiment, the resistance value of the resistor R6 is designed to be 50Ω, and the theoretical maximum surge current is 5.4A.

[0020] The input sampling and comparison circuit includes sampling resistors R7 to R10, anti-interference capacitor C3, sampling voltage comparator N1, and protection Zener diode V4. Specifically: one end of resistor R7 is connected to the positive terminal of the power supply input Vin; the other end of resistor R7 is connected to one end of resistor R8; the other end of resistor R8 is connected to one end of resistor R9; the other end of resistor R9 is connected to one end of resistor R10, one end of capacitor C3, and the reference voltage terminal of voltage comparator N1 (431); the other end of resistor R10 is connected to the other end of capacitor C3, the anode of voltage comparator N1 (431), and the anode of Zener diode V4; the cathode of voltage comparator N1 (431) is connected to the cathode of Zener diode V4. The input sampling and comparison circuit samples, divides, and compares the input power supply voltage. At the moment of power-on, the voltage divided by resistor R10 is close to 0V, and the reference voltage set inside voltage comparator N1 (431) is 2.5V. At this time, the comparison voltage is less than the reference voltage, and voltage comparator N1 (431) remains in the off state. When the comparison voltage increases to 2.5V as the power supply rises, the comparison voltage is greater than the reference voltage. At this point, the voltage comparator turns on to provide a path for subsequent circuits.

[0021] The isolation reverse connection protection circuit consists of only one isolation power diode, V3. The diode's anode is connected to the power input Vin+, one end of resistor R1, and one end of resistor R7; the diode's cathode is connected to the positive terminal of filter capacitor C2 and the positive terminal of the DC / DC converter power supply. This isolation reverse connection protection circuit primarily provides isolation for the input sampling circuit and the fast discharge reset circuit. When the power input is momentarily de-energized, it can block the instantaneous discharge of the fast discharge reset circuit voltage, maintaining the effective operation of the reset circuit's control function. This isolation power diode also provides reverse connection protection for the power supply system.

[0022] The fast discharge reset circuit includes current-limiting resistors R11 to R14, matching diode V5, and discharge optocoupler N2. Specifically: one end of resistor R11 is connected to the cathode of the anti-reverse diode; the other end of resistor R11 is connected to one end of resistor R12; the other end of resistor R12 is connected to one end of resistor R13; the other end of resistor R13 is connected to one end of resistor R14, the cathode of voltage comparator N1 (431), and the cathode of protection Zener diode V4; the other end of resistor R14 is connected to the anode of configuration diode V5; the cathode of configuration diode V5 is connected to the anode of the primary diode of optocoupler N2; the cathode of the primary diode of optocoupler N2 is connected to the other end of resistor R10, the other end of capacitor C3, the anode of voltage comparator N1 (431), and the anode of Zener diode; the collector of the secondary transistor of optocoupler N2 is connected to the gate (G) terminal of power MOSFET V2; and the emitter of the secondary transistor of optocoupler N2 is connected to the source (S) terminal of power MOSFET V2. When the input is powered down, when the voltage comparison voltage of voltage comparator N1 (431) is lower than its internal reference voltage (2.5V), voltage comparator N1 (431) is turned off. At this time, the fast discharge circuit starts to work, the primary side of optocoupler N2 is turned on, which in turn causes the secondary side to be turned on. Instantly, the gate drive voltage of power MOSFET V2 can be discharged in an approximate short circuit, forcing the power MOSFET to be turned off quickly, thus realizing fast reset discharge.

[0023] In the fast discharge reset circuit, in order to ensure the effective operation of the fast reset circuit, resistor R14 and diode V5 are used for anti-interference processing. The series conduction voltage of diode V5 is used to offset the clamping voltage after the voltage comparator N1 (431) is turned on. At the same time, resistor R4 is used for further current limiting to ensure that when the voltage comparator N1 (431) is turned on, the optocoupler N2 in the circuit can be effectively turned off, thereby improving the circuit's anti-interference capability and power supply robustness.

[0024] The technical solution and working principle of this invention are as follows: At the instant the power supply input is powered on, due to the presence of the delay capacitor C1, the driving voltage sampled and divided by R1 to R5 slowly rises from 0V. At this time, the driving gate-source voltage of the power MOSFET slowly rises from 0V, remaining in a closed state. The supply voltage starts charging the filter capacitor C2 through the current-limiting resistor R6. While the voltage is rising, the comparison voltage sampled by resistors R7 to R10 has not yet reached the internal reference voltage (2.5V) of the voltage comparator N1 (431). At this time, the primary and secondary sides of the optocoupler N2 in the fast discharge circuit are turned on, and the transistor on the secondary side clamps the driving gate-source voltage of the power MOSFET V2 at approximately 0.3V. This clamping voltage is lower than the power MOSFET's turn-on threshold, preventing it from turning on. At this time, the supply voltage continues to charge the filter capacitor through the current-limiting resistor R6. As the supply voltage continues to rise, when the sampling comparison voltage reaches the internal reference voltage (2.5V) of voltage comparator N1 (431), voltage comparator N1 (431) turns on, bypassing and cutting off optocoupler N2 in the fast discharge circuit. At this time, the clamping voltage applied by optocoupler N2 to the gate and source of the power MOSFET is removed, and power MOSFET V2 begins to conduct, shorting the current limiting resistor R6. The supply input voltage begins to quickly charge the filter capacitor C2 through the power MOSFET and provides power input to the downstream DC / DC power converter.

[0025] In this invention, the resistance values ​​of resistors R7, R8, and R9 are all 200KΩ, and the resistance value of resistor R10 is 10KΩ. Calculations show that when the sampling comparison voltage is 2.5V, the corresponding power supply input voltage is approximately 152.5V. When the power supply voltage is lower than this value, the power MOSFET V2 is in the off state; when the power supply voltage reaches this value, the power MOSFET V2, which was in the off state, begins to turn on, providing rapid charging for the downstream input capacitor C2. The downstream DC / DC converter's start-up threshold is at a power supply input of 200V, and the power-down hysteresis shutdown threshold is at 180V. This parameter setting ensures that during circuit operation, before the power MOSFET turns on for rapid charging, the downstream DC / DC converter circuit is in an inactive state. In the power supply input circuit, only the current-limiting resistor R6 charges the filter capacitor C2, and resistor R6 does not carry any power current. When the power supply voltage reaches the downstream DC / DC converter circuit's start-up threshold, the DC / DC converter circuit starts power output. At this time, the power MOSFET V2 has already been turned on and is ready to bear power output. In different specific solutions, reasonable parameter settings need to be made according to the actual situation in order to ensure that the circuit operates reliably in actual operation.

[0026] In this example, the device is a power supply switching power supply. The DC / DC converter in Figure 2 is also just an example. Its power supply equipment can also be of other different types. The specific device selection and parameter settings can be achieved by making simple changes to the scheme according to this invention.

[0027] This invention achieves electrical isolation between the input main circuit and the voltage sampling and comparison circuit by adding an input anti-reverse diode, thus enabling independent configuration of the input voltage sampling and comparison circuit and the fast discharge circuit. When the input power supply is off, the voltage sampling and comparison circuit can respond quickly and trigger the fast discharge mechanism. Simultaneously, utilizing the energy storage characteristics of the large input capacitor ensures that the fast discharge circuit continues to operate after power failure, thereby achieving rapid reset of the MOSFET gate-source voltage. During secondary rapid power-on, the circuit can fully execute the surge protection charging process, ensuring that the surge protection mechanism remains effective at all times, thereby significantly improving the reliability and surge resistance of the switching power supply under transient conditions.

[0028] This invention overcomes the technical bottleneck of the main power transistor drive circuit in the fast reset process in existing technologies through an innovative dynamic adjustment mechanism. This solution not only optimizes the response speed of the surge protection circuit but also ensures the reliability of fast reset through independently configured voltage sampling and comparison circuits and fast discharge circuits. Especially in applications using SiC (silicon carbide) devices, this circuit effectively overcomes the problem of incomplete gate-source voltage reset, preventing damage to the power transistor caused by inrush current during secondary power-on. This design significantly improves the stability and anti-interference capability of the switching power supply under high-frequency transient conditions, providing strong technical support for the stable operation of the switching power supply system.

[0029] Many specific details have been set forth in the foregoing description to provide a thorough understanding of the present invention. However, the above description is merely a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed above. Furthermore, any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A fast reset circuit for input surge current protection, characterized in that: It includes a charging switch circuit, an input sampling and comparison circuit, an isolation and reverse protection circuit, and a fast discharge reset circuit. The input sampling and comparison circuit and the isolation and reverse protection circuit are connected to the charging switch circuit. The isolation and reverse protection circuit electrically isolates the sampling point of the input sampling and comparison circuit from the sampling point of the fast discharge reset circuit. The operating point of the fast discharge reset circuit is set by the component parameters of the input sampling circuit. When the input is powered down, if the comparison voltage of the input sampling and comparison circuit is lower than its internal reference voltage, the fast discharge reset circuit starts to work, and the power MOSFET of the charging switch circuit is turned off, realizing fast reset discharge.

2. The input surge current protection and fast reset circuit according to claim 1, characterized in that: The charging switch circuit includes drive resistors R1 to R5, delay capacitor C1, protection Zener diode V1, power switching transistor V2, surge current limiting charging resistor R6, and filter capacitor C2. Specifically: one end of resistor R1 is connected to the overcurrent power supply input Vin+; the other end of resistor R1 is connected to one end of resistor R2; the other end of resistor R2 is connected to one end of resistor R3; the other end of resistor R3 is connected to one end of resistor R4; the other end of resistor R4 is connected to one end of capacitor C1, one end of resistor R5, the cathode of Zener diode V1, and the gate of power MOSFET V2; the other end of resistor R5 is connected to the power supply input Vin-, the other end of capacitor C1, the anode of Zener diode V1, the anode of Zener diode V1, one end of resistor R6, and the source of power MOSFET V1; the other end of power resistor R6 is connected to the drain of power MOSFET V3, the negative terminal of the DC / DC converter power supply, and the negative terminal of filter capacitor C2; the positive terminal of filter capacitor C2 is connected to the positive terminal of the DC / DC converter power supply.

3. The input surge current protection and fast reset circuit according to claim 1, characterized in that: The input sampling and comparison circuit includes sampling resistors R7 to R10, anti-interference capacitor C3, sampling voltage comparator N1, and protection Zener diode V4. Specifically: one end of resistor R7 is connected to the positive terminal of the power supply input Vin; the other end of resistor R7 is connected to one end of resistor R8; the other end of resistor R8 is connected to one end of resistor R9; the other end of resistor R9 is connected to one end of resistor R10, one end of capacitor C3, and the reference voltage terminal of voltage comparator N1; the other end of resistor R10 is connected to the other end of capacitor C3, the anode of voltage comparator N1, and the anode of Zener diode V4; and the cathode of voltage comparator N1 is connected to the cathode of Zener diode V4.

4. The input surge current protection and fast reset circuit according to claim 1, characterized in that: The isolation and anti-reverse circuit includes an isolation power diode V3, wherein: the anode of diode V3 is connected to the power supply input Vin+, one end of resistor R1, and one end of resistor R7 respectively; the cathode of diode V3 is connected to the positive terminal of filter capacitor C2 and the positive terminal of DC / DC converter power supply respectively.

5. The input surge current protection and fast reset circuit according to claim 1, characterized in that: The fast discharge reset circuit includes current-limiting resistors R11 to R14, matching diode V5, and discharge optocoupler N2. Specifically: one end of resistor R11 is connected to the cathode of the anti-reverse diode; the other end of resistor R11 is connected to one end of resistor R12; the other end of resistor R12 is connected to one end of resistor R13; the other end of resistor R13 is connected to one end of resistor R14, the cathode of voltage comparator N1, and the cathode of protection Zener diode V4; the other end of resistor R14 is connected to the anode of configuration diode V5; the cathode of configuration diode V5 is connected to the anode of the primary diode of optocoupler N2; the cathode of the primary diode of optocoupler N2 is connected to the other end of resistor R10, the other end of capacitor C3, the anode of voltage comparator N1, and the anode of Zener diode; the collector of the secondary transistor of optocoupler N2 is connected to the collector of power MOSFET V2; and the emitter of the secondary transistor of optocoupler N2 is connected to the source of power MOSFET V2.

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