Switching power supply input soft start circuit

Abstract

A switching power supply input soft start circuit, comprising: an optical coupling PC1, the anode of the light-emitting end of the optical coupling PC1 is connected with one end of an input end through a resistor R5, the cathode of the light-emitting end is connected with the other end of the input end, the collector of the optical coupling PC1 is connected with a voltage, and the emitter is grounded in sequence through a resistor R6 and a resistor R7; further comprising a switching tube TR1, the base of the switching tube TR1 is connected with the common connection point between the resistor R6 and the resistor R7, the emitter is grounded, the collector is connected with the voltage through a resistor R8 and a resistor R9; further comprising a switching tube TR2, the base of the switching tube TR2 is connected with the common connection point between the resistor R8 and the resistor R9, the collector is grounded through a resistor R11 and a resistor R10, and the emitter is connected with the voltage; further comprising a switching tube TR3, the gate of the switching tube TR3 is connected with the common connection point between the resistor R10 and the resistor R11, the drain is grounded, and the source is connected with an input voltage; a resistor R12 is further arranged between the input voltage and an output end, and a charging capacitor C3 is arranged between the anode and the cathode of the output end.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply circuits, and in particular to a soft-start circuit for switching power supply input. Background Technology

[0002] A large electrolytic capacitor is typically connected in parallel to the primary input of a switching power supply. At the moment the input voltage reaches its peak, since the initial voltage across the capacitor is zero, a very large charging current (inrush current) is generated according to I = C * dV / dt. The magnitude of this current depends on the input voltage, the total capacitance of the input capacitor, and the equivalent impedance of the input line. A buffer circuit connects an impedance in series in the charging circuit during the initial charging phase and then short-circuits or bypasses this impedance after charging is complete to reduce losses during normal operation. Currently, a common solution is a negative temperature coefficient thermistor (NTC) with a relay (or resistor) bypass. The NTC solution is simple, low-cost, and requires no additional control, but its applicability is limited. Its current handling capacity and hot resistance are not zero, making it unsuitable for high-power power supplies. NTCs require cooling time, therefore they are unsuitable for applications with frequent power-on / off cycles or rapid restarts, and their characteristics are easily affected by changes in ambient temperature. Relay bypass requires additional auxiliary power and control signals, and it is expensive, bulky, and has a limited mechanical lifespan. This approach is suitable for applications that are sensitive to cost and size, have high efficiency and reliability requirements, require frequent switching, and have high power. The circuit described below was designed to overcome the aforementioned technical problems. Utility Model Content

[0003] To address the aforementioned issues, this technical solution provides a soft-start circuit for the input of a switching power supply.

[0004] To achieve the above objectives, the technical solution is as follows:

[0005] A soft-start circuit for input of a switching power supply, comprising:

[0006] Optical coupler PC1, the positive terminal of the light-emitting end of the optical coupler PC1 is connected to one end of the input end through resistor R5, the negative terminal of the light-emitting end is connected to the other end of the input end, the collector of the optical coupler PC1 is connected to a voltage, and the emitter is grounded in sequence through resistor R6 and resistor R7.

[0007] It also includes a switching transistor TR1, the base of which is connected to the common junction between resistors R6 and R7, the emitter is grounded, and the collector is connected to the voltage through resistors R8 and R9.

[0008] It also includes a switching transistor TR2, the base of which is connected to the common junction between resistors R8 and R9, the collector is grounded through resistors R11 and R10, and the emitter is connected to the voltage.

[0009] It also includes a switching transistor TR3, whose gate is connected to the common junction between resistors R10 and R11, its drain is grounded, and its source is connected to the input voltage.

[0010] A resistor R12 is provided between the input voltage and the output terminal, and a charging capacitor C3 is connected between the positive and negative terminals of the output terminal.

[0011] In some embodiments, the gate of the switching transistor TR3 is also grounded through the Zener diode ZD1.

[0012] In some embodiments, a resistor R5 and a capacitor C1 are connected between the positive and negative terminals of the light-emitting end of the optocoupler PC1.

[0013] In some embodiments, the capacitor C1 is connected in parallel with a resistor R4.

[0014] In some embodiments, the input terminal is connected to the optocoupler PC1 via resistor R1 and diode unit DA1, resistor R2 and diode unit DA2, and resistor R3 and diode unit DA3, respectively.

[0015] The beneficial effects of this application are:

[0016] This power-on buffer circuit can be used to limit the inrush current generated when a small to medium power switching power supply is powered on, and is also suitable for applications requiring frequent power-on and power-off. The circuit consists of a power-on detection circuit, an isolation circuit, a MOS drive circuit, and a buffer bypass circuit. The power-on detection circuit consists of clamping diodes and current-limiting resistors; a pair of series diodes replaces the rectifier bridge, saving space and reducing circuit cost. The isolation circuit converts the detected input power-on signal into a control signal using an optocoupler, achieving isolation between the high-voltage and control signals. The MOS drive circuit uses the isolated control signal, amplified by two stages, to generate the MOS drive signal. The buffer bypass circuit consists of a buffer resistor and a MOS transistor connected in parallel. During power-on, the buffer resistor charges the bus capacitor; once the bus is fully charged, the MOS transistor conducts, bypassing the buffer resistor to reduce energy loss. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this utility model, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0018] Figure 1 This is a structural schematic diagram of an embodiment of the present utility model. Detailed Implementation

[0019] To make the technical problems solved, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0020] Please refer to Figure 1 As shown, a switching power supply input soft-start circuit includes:

[0021] Optical coupler PC1, the positive terminal of the light-emitting end of the optical coupler PC1 is connected to one end of the input end through resistor R5, the negative terminal of the light-emitting end is connected to the other end of the input end, the collector of the optical coupler PC1 is connected to a voltage, and the emitter is grounded in sequence through resistor R6 and resistor R7.

[0022] It also includes a switching transistor TR1, the base of which is connected to the common junction between resistors R6 and R7, the emitter is grounded, and the collector is connected to the voltage through resistors R8 and R9.

[0023] It also includes a switching transistor TR2, the base of which is connected to the common junction between resistors R8 and R9, the collector is grounded through resistors R11 and R10, and the emitter is connected to the voltage.

[0024] It also includes a switching transistor TR3, whose gate is connected to the common junction between resistors R10 and R11, its drain is grounded, and its source is connected to the input voltage.

[0025] A resistor R12 is provided between the input voltage and the output terminal, and a charging capacitor C3 is connected between the positive and negative terminals of the output terminal.

[0026] In this embodiment, the gate of the switching transistor TR3 is also grounded through the Zener diode ZD1.

[0027] In this embodiment, a resistor R5 and a capacitor C1 are connected between the positive and negative terminals of the light-emitting end of the optocoupler PC1.

[0028] In this embodiment, the capacitor C1 is connected in parallel with a resistor R4.

[0029] In this embodiment, the input terminal is connected to the optocoupler PC1 via resistor R1 and diode unit DA1, resistor R2 and diode unit DA2, and resistor R3 and diode unit DA3, respectively.

[0030] The power-on buffer circuit consists of a charging circuit and a bypass circuit. P++ charges the bus capacitor C3 through the charging resistor R12. The MOSFET TR3 is connected in parallel with R12, with its drain connected to P++ and its source connected to the positive terminal of the bus capacitor C3. After it is turned on, the resistor is shorted by the MOSFET.

[0031] The power-on detection circuit inputs N phases (three-phase, two-phase, or single-phase) of high-voltage AC power to the N series diode nodes via current-limiting resistors. The anodes and cathodes of a pair of series diodes are connected together. The cathode, as the positive voltage, is connected to the anode of the primary side of the optocoupler via current-limiting resistor R5, and the anode, as the negative voltage, is connected to the cathode of the primary side of the optocoupler. The collector of the secondary side of the optocoupler is connected to the secondary side drive power supply, and the emitter is connected to the reference ground of the drive power supply via current-limiting resistors R6 and R7. The drive power supply uses the positive terminal of the bus electrolytic capacitor as the reference ground.

[0032] The MOSFET is a voltage-driven device. The driving circuit mainly consists of TR1 (NPN type) and TR2 (PNP type). The emitter of TR1 is connected to the reference ground, the base is connected to the voltage divider point of R6 and R7, and the collector is connected to the driving power supply through the current-limiting resistors R8 and R9. The main function of TR1 is to amplify the secondary current of the optocoupler and increase the driving current of TR2. The emitter of TR2 is connected to the driving power supply, and the collector is connected to the gate of the MOSFET TR3 through the driving resistor R11. The base is connected to the voltage divider point of R8 and R9. Resistor R10 and TVS diode ZD1 are connected in parallel between the gate and source of the MOSFET as a protection device.

[0033] The above description is only a preferred embodiment of this application and is not intended to limit the scope of implementation of this application. Any other embodiments whose principles and basic structures are the same as or similar to those of this application are within the protection scope of this application.

Claims

1. A soft-start circuit for a switching power supply input, characterized in that, include; Optical coupler PC1, the positive terminal of the light-emitting end of the optical coupler PC1 is connected to one end of the input end through resistor R5, the negative terminal of the light-emitting end is connected to the other end of the input end, the collector of the optical coupler PC1 is connected to a voltage, and the emitter is grounded in sequence through resistor R6 and resistor R7. It also includes a switching transistor TR1, the base of which is connected to the common junction between resistors R6 and R7, the emitter is grounded, and the collector is connected to the voltage through resistors R8 and R9. It also includes a switching transistor TR2, the base of which is connected to the common junction between resistors R8 and R9, the collector is grounded through resistors R11 and R10, and the emitter is connected to the voltage. It also includes a switching transistor TR3, whose gate is connected to the common junction between resistors R10 and R11, its drain is grounded, and its source is connected to the input voltage. A resistor R12 is provided between the input voltage and the output terminal, and a charging capacitor C3 is connected between the positive and negative terminals of the output terminal.

2. The soft-start circuit for a switching power supply input according to claim 1, characterized in that: The gate of the switching transistor TR3 is also grounded through the Zener diode ZD1.

3. The soft-start circuit for a switching power supply input according to claim 1, characterized in that: A resistor R5 and a capacitor C1 are connected between the positive and negative terminals of the light-emitting end of the optocoupler PC1.

4. The soft-start circuit for a switching power supply input according to claim 3, characterized in that: The capacitor C1 is connected in parallel with a resistor R4.

5. The soft-start circuit for a switching power supply input according to claim 3, characterized in that: The input terminals are connected to the optocoupler PC1 via resistor R1 and diode unit DA1, resistor R2 and diode unit DA2, and resistor R3 and diode unit DA3, respectively.

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