A power supply circuit with soft start function

Abstract

The application relates to a power supply circuit with a soft start function, characterized in that the power supply circuit comprises a soft start circuit (1), a control circuit (2) and a main power supply circuit (3); the main power supply circuit (3) comprises a switching device, one end of the control end of the switching device is connected with a power supply through the soft start circuit (1), the other end is grounded through a switching tube in the control circuit (2), the control end of the switching tube is connected in parallel with a voltage division resistor for turning on the switching tube; the on-off port of the switching device is connected in series between the power supply and the output end of the power supply circuit; the soft start circuit (1) comprises a current limiting circuit. The application solves the problem that, in the prior art, when the inrush current is inhibited, a larger channel loss or on loss is introduced, the inrush current is large when the on loss is small, and the inrush current and the on loss are difficult to balance.

Description

Technical Field

[0001] This invention relates to a power supply circuit with soft-start function, belonging to the field of switching circuit technology. Background Technology

[0002] In ultra-high voltage flexible direct current transmission systems, the hardware power supply of the converter valve control cabinet adopts a cross-redundant power supply method to ensure power supply stability. To improve power quality, capacitors are equipped in the front stage of the load for energy storage and filtering. During the power-on process of the load board, capacitive components in the board will generate inrush current, which can damage the components and may even cause false triggering of short-circuit protection. Therefore, it is necessary to add a power-on soft-start circuit to the load board to suppress the power-on inrush current. Commonly used soft-start circuits will cause conduction losses, which are usually dissipated in the form of heat. When suppressing the power-on inrush current, they will introduce a large conduction loss, or when the conduction loss is small, the power-on inrush current is large, making it difficult to balance the power-on inrush current and conduction loss. Summary of the Invention

[0003] The purpose of this invention is to provide a power supply circuit with soft-start function to solve the problems of existing technology where large channel losses are introduced when suppressing power-on inrush current, or large power-on inrush current and difficulty in balancing power-on inrush current and conduction losses when conduction losses are small.

[0004] To achieve the above objectives, the present invention provides a power supply circuit with a soft-start function, comprising a soft-start circuit (1), a control circuit (2), and a main power supply circuit (3). The main power supply circuit (3) includes a switching device. One end of the switching device's conduction control terminal is connected to the power supply, and the other end is grounded through a switching transistor in the control circuit (2). A voltage divider circuit for conducting the switching transistor is connected in parallel to the control terminal of the switching transistor. The on / off port of the switching device is connected in series between the power supply input terminal and the power supply circuit output terminal. When the voltage difference at the conduction control terminal reaches a set value, the on / off port of the switching device is turned on to supply power to the load. A load capacitor is also connected in parallel across the voltage divider circuit. When the power supply circuit is powered on, the load capacitor is charged through the soft-start circuit. When the voltage across the load capacitor reaches a certain value, the switching transistor is turned on through the voltage divider circuit.

[0005] The present invention provides a power supply circuit with soft start in a power supply system, which can limit the inrush current generated when the load is powered on, protect the components from damage by the inrush current, and avoid false triggering of the overcurrent protection on the bus; at the same time, it has low conduction loss and can be used under heavy load conditions.

[0006] Furthermore, the power supply circuit with soft-start function described in this invention further includes a current-limiting circuit, which includes a current-limiting transistor. The emitter of the current-limiting transistor is connected to the load capacitor through a first resistor, the collector is used to connect to the power supply, and a second resistor is connected in parallel between the base and the collector. When the power supply circuit is powered on, the current-limiting transistor is turned on through the second resistor, and the load capacitor is charged.

[0007] The current limiting circuit uses switching devices to limit the output current. During power-on, the power supply current flows from the current limiting circuit to the load, limiting the inrush current during power-on.

[0008] Furthermore, in the power supply circuit with soft-start function described in this invention, the current limiting circuit further includes a third resistor connected between the base of the current limiting transistor and the output terminal of the soft-start circuit to provide negative feedback.

[0009] The third resistor provides negative feedback for the output current, which is used to limit the output current of the current-limiting transistor in the current-limiting circuit, i.e., to limit the power-on current.

[0010] Furthermore, in the power supply circuit with soft-start function described in this invention, the switching device includes a first MOSFET and a second MOSFET connected at their sources. The gates of both the first MOSFET and the second MOSFET are grounded through the switching transistor. A voltage divider resistor is connected in parallel between the gate and drain of the first MOSFET. The drain of the first MOSFET is used to connect to the power supply, and the drain of the second MOSFET is connected to the output terminal of the power supply circuit. The drain of the first MOSFET and the drain of the second MOSFET constitute the on / off port.

[0011] By placing two MOSFETs opposite each other, the characteristic of the MOSFET's parasitic diode that only allows unidirectional current to pass through can be utilized to achieve the function of preventing current backflow. At the same time, it can also prevent current from flowing from the power supply to the load through the parasitic diode when power is applied.

[0012] Furthermore, in the power supply circuit with soft-start function described in this invention, a buffer capacitor is connected in parallel between the gate and drain of the first MOS transistor. As the voltage across the buffer capacitor increases, the load current of the first MOS transistor gradually increases.

[0013] Connecting a buffer capacitor in parallel between the gate and drain of the first MOSFET can slowly and gradually increase the current flowing through the first MOSFET, thereby improving circuit stability.

[0014] Furthermore, the power supply circuit with soft-start function described in this invention further includes a diode connected in series between the gate of the second MOS transistor and the switching transistor to prevent reverse voltage in the main power supply circuit.

[0015] By placing a diode connected in series between the gate of the second MOSFET and the output terminal of the main power supply circuit, other components in the main power supply circuit can be prevented from being subjected to reverse voltage.

[0016] Furthermore, in the power supply circuit with soft-start function described in this invention, the switching transistor is a bipolar transistor, and the collector and emitter of the bipolar transistor are connected in series between the gate of the second MOSFET and ground.

[0017] Furthermore, in the power supply circuit with soft-start function described in this invention, the voltage divider circuit includes a Zener diode and a voltage divider resistor connected in series, and the base of the transistor is grounded through the voltage divider resistor.

[0018] Furthermore, the power supply circuit with soft-start function described in this invention further includes a coupling circuit composed of several diodes connected in parallel; the input end of the coupling circuit is used to connect to the power supply point, and the output end is connected to the collector of the current-limiting transistor.

[0019] A coupling circuit consisting of several diodes connected in parallel is set up in the soft start circuit. Because the current of the diode flows in one direction, it can prevent the current of one power supply from flowing to another power supply.

[0020] Furthermore, the power supply circuit with soft-start function described in this invention has several main power supply circuits connected in parallel, and each main power supply circuit is used to connect between the corresponding power supply and the output terminal of the power supply circuit.

[0021] Setting up multiple main power supply circuits, with each main power supply circuit connected to a corresponding power source, can prevent the entire circuit from becoming unusable when one or more main power supply circuits fail, thus making the circuit more stable. Attached Figure Description

[0022] Figure 1 This embodiment is a power supply circuit with soft-start function;

[0023] Figure 2 These are the voltage and current waveforms of the soft-start circuit in this embodiment when it is powered on. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] An embodiment of a power supply circuit with soft-start function:

[0026] like Figure 1The power supply circuit with soft-start function in this embodiment includes a soft-start circuit 1, a control circuit 2, a main power supply circuit, an equivalent power supply 5, and an equivalent load 6. The equivalent load 6 is composed of a capacitor in series with a resistor, which respectively represent the capacitive load and the resistive load in the equivalent load.

[0027] In other implementations, to improve power supply reliability, the main power supply circuit includes multiple circuits connected in series, such as the first main power supply circuit 3, the second main power supply circuit, ..., the nth main power supply circuit 4 (n = 1, 2, 3, ...) in this embodiment. Correspondingly, each main power supply circuit is connected to a corresponding power supply, such as the power supply POWER-1, the power supply POWER-2, ..., the power supply POWER-n (n = 1, 2, 3, ...) in this embodiment.

[0028] The soft-start circuit 1 includes a coupling circuit and a current-limiting circuit, connected in series between the equivalent load 6 and the equivalent power supply 5, limiting the inrush current of the capacitive load during power-up. The coupling circuit consists of diodes D1, D2, ..., Dn (n = 1, 2, 3, ...) connected in parallel, with their cathodes connected together and their anodes connected to the positive outputs of the two power supplies respectively. The current-limiting circuit includes a transistor T2. The emitter of transistor T2 is connected to the output of the current-limiting circuit via a series resistor R3, and the collector of transistor T2 is connected to the input of the current-limiting circuit. The base of transistor T2 is connected to the emitter of transistor T2 via resistor R2, and the base of transistor T2 is connected to the output of the coupling circuit via resistor R1. The current-limiting circuit uses switching devices to form a current negative feedback network to limit the output current.

[0029] The first main power supply circuit 3 includes two MOSFETs, a first MOSFET Q1-1 and a second MOSFET Q1-2. The source of the first MOSFET Q1-1 is connected to the source of the second MOSFET Q1-2. The parasitic diodes of the two MOSFETs are used to prevent reverse current flow and also to prevent current from flowing from the power supply to the load through the parasitic diodes during power-on. The gates of the two MOSFETs are connected to ensure that each MOSFET is turned on and off simultaneously. A capacitor C1-1 is connected in parallel between the source and drain of the first MOSFET Q1-1, and is pulled down to ground by a resistor R5 in the control circuit 2. The inrush current of the main power supply circuit is controlled by the parameters of the capacitor and resistor.

[0030] The second main power supply circuit, the third main power supply circuit, ..., the nth main power supply circuit (n = one, two, three, ...) have the same structure and components as the first main power supply circuit 3, and have the same function. They serve as redundant backups for each other to ensure reliable power supply. They will not be described in detail here.

[0031] Control loop 2 includes transistor T1, whose base is connected to the output of soft-start loop 1 via series resistor R4 and Zener diode Z1. Its emitter is pulled down to the negative terminal of the equivalent power supply 5 via resistor R5, and its collector is connected to the gate of the second MOS transistor Qn-2 (n = 1, 2, 3, ...) in each main power supply loop. Control loop 2 obtains feedback signals from the load voltage and uses the switching device transistor T1 to control the switching on and off of all main power supply loops.

[0032] like Figure 2 The voltage and current waveforms of the soft-start circuit in this embodiment are shown during power-on. During power-on, the voltage and current change curves with time, sharing the same time axis. t1 to t5 are time points used for illustrative purposes only. The waveforms represent the load voltage U... out Load current I out Soft start circuit current I o Main power supply circuit current I i , where I o =I1+I2+…+I n .

[0033] At time t1, switches S1 and S2 are closed. Due to the presence of the parasitic diode in the MOS transistor, current cannot be conducted. At this time, the voltage across capacitor C2 is 0V, transistor T1 is not conducting, and the voltage difference across capacitors C1-1, C2-1, ..., Cn-1 (n = 1, 2, 3, ...) in the main power supply circuit is 0V. The voltage difference between the gate and source of the MOS transistor is 0V, and the MOS transistor is turned off.

[0034] The power supply output is coupled through diodes D1, D2...Dn (n=1,2,3,...). Since the load voltage is 0V, the collector junction of the transistor is reverse-biased and the emitter junction is forward-biased, putting it in amplification mode. The main current flows from the collector to the emitter of transistor T2, charging the load capacitor C2. The power supply provides current to the base through R1, and R2 provides negative feedback for the output current, limiting the output current of transistor T2, i.e., limiting the inrush current. During t1 to t2, the MOSFETs are not conducting, and the load current slowly decreases from its peak value to the stable value of the current limiting circuit. Since T2 is in amplification mode, the voltage across T2 and R1 limits the load voltage.

[0035] As the load capacitor C2 charges, the load voltage rises. When the voltage of C2 reaches the breakdown voltage of the Zener diode Z1, the emitter junction of T1 begins to forward bias, and transistor T1 turns on. With T1 conducting, capacitors C1-1, C2-1, ..., Cn-1 (n = 1, 2, 3, ...) are connected to ground through current-limiting resistor R5. Capacitors C1-1, C2-1, ..., Cn-1 (n = 1, 2, 3, ...) begin to charge, and the voltage difference between the gate and source of the MOSFET begins to increase, i.e., during the period t2 to t3. At this time, because the voltage difference between the gate and source has not reached the turn-on voltage, the MOSFET is in the off state, and there is no current in the main power supply circuit. Diodes D1-1, D2-1, ..., Dn-1 (n = 1, 2, 3, ...) can prevent C1-1, C2-1, ..., Cn-1 (n = 1, 2, 3, ...) from being subjected to reverse voltage.

[0036] During the period t3 to t4, the voltage difference between the gate and source reaches the turn-on voltage, and the MOS transistor turns on. However, at this time, the conductive channel between the source and drain is relatively narrow, and the on-resistance is relatively large. At this time, current flows from both the MOS transistor and transistor T2 to the load capacitor C2. As the buffer capacitors C1-1, C2-1, ..., Cn-1 (n = 1, 2, 3, ...) charge, the on-resistance of the MOS transistor gradually decreases, the load current of the MOS transistor gradually increases, and the current flowing through transistor T2 gradually decreases.

[0037] At time t4, when the current of transistor T2 decreases to 0, the current of the MOS transistor equals the load current. The load capacitor is not yet fully charged. At this time, the on-resistance between the source and drain of the MOS transistor is relatively low, and there is still a partial inrush current. This current gradually decreases as the load capacitor C2 charges until it reaches the load current. The load voltage gradually increases as the load capacitor C2 charges, i.e., during the period from t4 to t5. This inrush current can be controlled by adjusting the voltage drop of the Zener diode Z1 or the capacitance values ​​of capacitors C1-1, C2-1, ..., Cn-1 (n = 1, 2, 3, ...).

[0038] After time t5, the load current and load voltage reach a stable state, and the soft-start circuit can be considered to be disconnected. The load current flows from the main power supply circuit to the load. The conduction loss of the main power supply circuit mainly comes from the MOS. Since the on-resistance of the MOS is extremely small, the conduction loss of this circuit is extremely small, which has the effect of suppressing the power-on inrush current.

Claims

1. A power supply circuit with soft-start function, characterized in that, It includes a soft-start circuit (1), a control circuit (2), and a main power supply circuit (3); the main power supply circuit (3) includes a switching device, one end of the switching device's conduction control terminal is used to connect to the power supply, and the other end is grounded through the switching tube in the control circuit (2). The control terminal of the switching tube is connected in parallel with a voltage divider circuit for conducting the switching tube; the on / off port of the switching device is connected in series between the power supply input terminal and the power supply circuit output terminal. When the voltage difference at the conduction control terminal reaches a set value, the on / off port of the switching device is turned on to supply power to the load; a load capacitor is also connected in parallel across the voltage divider circuit. When the power supply circuit is powered on, the load capacitor is charged through the soft-start circuit. When the voltage across the load capacitor reaches a certain value, the switching tube is turned on through the voltage divider circuit.

2. The power supply circuit with soft-start function according to claim 1, characterized in that, The soft-start circuit also includes a current-limiting circuit, which includes a current-limiting transistor. The emitter of the current-limiting transistor is connected to the load capacitor through a first resistor, the collector is used to connect to the power supply, and a second resistor is connected in parallel between the base and the collector. When the power supply circuit is powered on, the current-limiting transistor is turned on through the second resistor and the load capacitor is charged.

3. The power supply circuit with soft-start function according to claim 2, characterized in that, The current-limiting circuit also includes a third resistor connected between the base of the current-limiting transistor and the output of the soft-start circuit to provide negative feedback.

4. The power supply circuit with soft-start function according to claim 1, characterized in that, The switching device includes a first MOSFET and a second MOSFET connected at their sources. The gates of both the first MOSFET and the second MOSFET are grounded through the switching transistor. A voltage divider resistor is connected in parallel between the gate and drain of the first MOSFET. The drain of the first MOSFET is used to connect to the power supply, and the drain of the second MOSFET is connected to the output terminal of the power supply circuit. The drain of the first MOSFET and the drain of the second MOSFET constitute the on / off port.

5. The power supply circuit with soft-start function according to claim 4, characterized in that, A buffer capacitor is connected in parallel between the gate and drain of the first MOSFET. As the voltage across the buffer capacitor increases, the load current of the first MOSFET gradually increases.

6. The power supply circuit with soft-start function according to claim 4, characterized in that, The main power supply circuit also includes a diode connected in series between the gate of the second MOSFET and the switching transistor to prevent reverse voltage.

7. The power supply circuit with soft-start function according to claim 1, characterized in that, The switching transistor is a bipolar transistor, with its collector and emitter connected in series between the gate of the second MOSFET and ground.

8. The power supply circuit with soft-start function according to claim 7, characterized in that, The voltage divider circuit includes a Zener diode and a voltage divider resistor connected in series, and the base of the transistor is grounded through the voltage divider resistor.

9. The power supply circuit with soft-start function according to claim 2, characterized in that, The soft-start circuit also includes a coupling circuit consisting of several diodes connected in parallel; the input end of the coupling circuit is used to connect to the power supply at the power supply point, and the output end is connected to the collector of the current-limiting transistor.

10. The power supply circuit with soft-start function according to claim 1, characterized in that, There are several main power supply circuits connected in parallel, each main power supply circuit being used to connect between the corresponding power supply and the output terminal of the power supply circuit.

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