A regulating circuit for reducing input surge current of switching power supply

Abstract

The present invention relates to a regulation circuit for reducing the input surge current of a switching power supply. The regulation circuit is connected between a PFC circuit and a DCDC circuit. The regulation circuit includes a capacitor C1, a capacitor C2, a thyristor (SCR) Q1, a resistor R1, a diode D2, and a power supply VCC. The capacitors C1 and C2 are connected in parallel between the PFC circuit and the DCDC circuit. The resistor R1 is connected between the capacitors C1 and C2. The positive electrode of the diode D2 is connected to the capacitor C1, and the negative electrode is connected to the capacitor C2. The anode of the thyristor Q1 is connected to the capacitor C2, the cathode is connected to the capacitor C1, and the control electrode is connected to the power supply VCC. Compared with the existing technology, the present invention has the advantages of solving the problem of power supply damage caused by the loss of SCR drive.

Description

Technical Field

[0001] The invention relates to a switching power supply, in particular to a regulating circuit for reducing input surge current of the switching power supply. Background Art

[0002] The startup inrush current of a switching power supply is typically very large. A common approach to limiting this current is to use a small-value NTC resistor. However, this NTC resistor has little limiting effect when the power supply is turned on in a hot state. When multiple power supplies are connected in parallel, the combined inrush current can be significant, potentially damaging the circuit or tripping the circuit breaker. Special applications, such as explosion-proof applications, require strict limits on the switching power supply's inrush current, I^2t. Common limiting methods are as follows:

[0003] Solution 1: Use a bidirectional thyristor in series with the input terminal and use a zero-crossing detection photo-thyristor to control the conduction of the thyristor. In this way, when AC input is applied, the thyristor will naturally conduct at 0 degrees, and the inrush current will be very small.

[0004] The disadvantages of solution 1 are very obvious. It requires an expensive photosilicon and is only suitable for AC input. If the switching power supply uses DC input, this solution will not be effective. In other words, it has problems such as high cost and narrow application range.

[0005] Option 2: Connect a single-phase thyristor in series after the rectifier bridge (with a fixed resistor in parallel), and then make an auxiliary power supply part to power the thyristor separately. When starting up, the fixed resistor in the circuit limits the inrush current, and the thyristor is turned on after a fixed delay.

[0006] Option 2 requires a separate power supply unit for the thyristors. This also presents a critical weakness: if the thyristor power supply winding loses power after the power supply stops, a fixed resistor will be connected in series with the circuit. If a large lightning current is injected at this time, a voltage drop of several hundred volts will occur across this resistor, potentially damaging the entire power supply. This presents a fatal risk and necessitates the addition of a separate thyristor power supply unit. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a regulating circuit for reducing the input surge current of a switching power supply. The circuit solves the problem of power supply damage after the thyristor (SCR) drive is lost.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A regulating circuit for reducing the input surge current of a switching power supply is connected between a PFC circuit and a DCDC circuit. The regulating circuit includes a capacitor C1, a capacitor C2, a thyristor Q1, a resistor R1, a diode D2, and a power supply VCC. The capacitors C1 and C2 are connected in parallel and connected between the PFC circuit and the DCDC circuit. The resistor R1 is connected between the capacitors C1 and C2. The positive electrode of the diode D2 is connected to the capacitor C1, and the negative electrode is connected to the capacitor C2. The anode of the thyristor Q1 is connected to the capacitor C2, the cathode is connected to the capacitor C1, and the control electrode is connected to the power supply VCC.

[0010] Preferably, the capacitance ratio of the capacitor C1 to the capacitor C2 is 1:10000 to 1:2, preferably 1:100.

[0011] Preferably, the PFC circuit adopts an active PFC circuit.

[0012] Preferably, the active PFC circuit includes an inductor L1, a MOS transistor Q2 and a diode D1. The inductor L1 is connected to the drain of the MOS transistor Q2 and the anode of the diode D1 respectively. The cathode of the diode D1 is connected to the anode of the capacitor C1 and the anode of the capacitor C2 respectively.

[0013] Preferably, the DCDC circuit includes a transformer and a MOS transistor Q3 , and the primary coil of the transformer is connected to the positive electrode of the capacitor C2 and the drain of the MOS transistor Q3 respectively.

[0014] Preferably, the secondary coil of the transformer is output through a diode D4.

[0015] Preferably, the winding Nvcc of the power supply VCC is linearly coupled to the primary coil of the transformer.

[0016] Preferably, one end of the winding Nvcc is connected to the input end of the power supply VCC through a diode D3, and the other end of the winding Nvcc is connected to the source of the MOS transistor Q3.

[0017] Preferably, when the PFC circuit is in boost operation, the capacitor C2 is charged via the thyristor Q1, and the capacitor C2 discharges to the capacitor C1 via the diode D2.

[0018] Preferably, the VCC power supply drives the thyristor Q1 to turn on, and the capacitors C1 and C2 are connected in parallel to ensure that the power circuit operates normally at full power.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1) This solves the problem of power supply damage caused by SCR drive loss. Even if the power supply stops working and there is no drive voltage (and the current flowing through the SCR is less than the holding current), the surge is first injected into the small capacitor, causing a small voltage drop across the resistor that limits the surge current. This prevents power supply failure.

[0021] 2) No separate thyristor power supply unit is required, and the VCC of the power supply IC can be used. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a specific circuit diagram of the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0024] like Figure 1 As shown, a regulation circuit for reducing the input inrush current of a switching power supply is connected between the PFC circuit and the DCDC circuit. The regulation circuit includes a capacitor C1, a capacitor C2, a thyristor Q1, a resistor R1, a diode D2, and a power supply VCC. The capacitors C1 and C2 are connected in parallel and connected between the PFC circuit and the DCDC circuit. The resistor R1 is connected between the capacitors C1 and C2. The positive electrode of the diode D2 is connected to the capacitor C1, and the negative electrode is connected to the capacitor C2. The anode of the thyristor Q1 is connected to the capacitor C2, the cathode is connected to the capacitor C1, and the control electrode is connected to the power supply VCC.

[0025] The PFC circuit adopts an active PFC circuit. The active PFC circuit includes an inductor L1, a MOS transistor Q2, and a diode D1. The inductor L1 is connected to the drain of the MOS transistor Q2 and the anode of the diode D1, respectively. The cathode of the diode D1 is connected to the anode of the capacitor C1 and the anode of the capacitor C2, respectively.

[0026] The DC-DC circuit includes a transformer and a MOS transistor Q3. The transformer's primary winding is connected to the positive electrode of capacitor C2 and the drain of MOS transistor Q3, respectively. The transformer's secondary winding outputs power via diode D4. Winding Nvcc of power supply VCC is linearly coupled to the transformer's primary winding. One end of winding Nvcc is connected to the input of power supply VCC via diode D3, and the other end of winding Nvcc is connected to the source of MOS transistor Q3.

[0027] This invention divides the large filtering capacitor of the switching power supply's PFC output into two parallel capacitors. A small capacitor is directly connected to the power circuit. When the power circuit operates, it generates a voltage that powers the IC. This voltage drives the SCR, which is then connected in parallel with the large capacitor. This allows the SCR to be connected in parallel with the large capacitor. This allows only the small capacitor to be present in the circuit when the switching power supply is turned on. This minimizes the inrush current I²t. While the power conversion unit performs a soft start, the circuit charges the large capacitor through a fixed resistor. After the power conversion unit is turned on, the thyristor is electrically conductive, and the large and small capacitors operate in parallel.

[0028] The specific working process is as follows:

[0029] like Figure 1 As shown, the capacitors behind the PFC are C1 and C2, with resistors R1, D2, and Q1 between them. When the switching power supply is powered on, only a small capacitor, C1, is in the circuit, and C2 is charged through R1. After C1 is energized, the switching power supply's power circuit begins soft-start operation. During the soft-start process (typically lasting more than 500ms), the transformer winding, VCC, is energized, the control IC operates, and VCC drives thyristor Q1. After SCR Q1 turns on, capacitors C1 and C2 are connected in parallel, ensuring full power and normal operation of the power circuit. During PFC boost operation, C2 is charged through Q1, and C2 discharges to C1 through diode D2. Physically, C2 and C1 are connected in parallel.

[0030] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A regulating circuit for reducing the input surge current of a switching power supply, the regulating circuit being connected between a PFC circuit and a DCDC circuit, characterized in that: The regulation circuit includes capacitor C1, capacitor C2, thyristor Q1, resistor R1, diode D2 and power supply VCC. The capacitor C1 and capacitor C2 are connected in parallel between the PFC circuit and the DCDC circuit. The resistor R1 is connected between the capacitor C1 and capacitor C2. The positive electrode of the diode D2 is connected to the capacitor C1, and the negative electrode is connected to the capacitor C2. The anode of the thyristor Q1 is connected to the capacitor C2, the cathode is connected to the capacitor C1, and the control electrode is connected to the power supply VCC. The VCC power supply drives the thyristor Q1 to conduct, and the capacitors C1 and C2 are connected in parallel to ensure that the power circuit operates normally at full power; When the switching power supply is powered on, only capacitor C1 is in the circuit, and C2 is charged through R1. After C1 is energized, the switching power supply power circuit begins soft-start operation. During the soft-start process, the transformer winding VCC is energized, the control IC works, and VCC drives the thyristor Q1. After the thyristor Q1 is turned on, capacitors C1 and C2 are connected in parallel to ensure that the power circuit operates normally at full power. When the PFC circuit is in boost operation, the capacitor C2 is charged via the thyristor Q1, and the capacitor C2 discharges to the capacitor C1 via the diode D2.

2. The regulating circuit for reducing the input surge current of a switching power supply according to claim 1, characterized in that: The capacitance ratio of the capacitor C1 to the capacitor C2 is 1:10000 to 1:

2.

3. The regulating circuit for reducing the input surge current of a switching power supply according to claim 1, characterized in that: The PFC circuit adopts an active PFC circuit.

4. The regulating circuit for reducing the input surge current of a switching power supply according to claim 3, characterized in that: The active PFC circuit includes an inductor L1, a MOS transistor Q2 and a diode D1. The inductor L1 is connected to the drain of the MOS transistor Q2 and the anode of the diode D1 respectively. The cathode of the diode D1 is connected to the anode of the capacitor C1 and the anode of the capacitor C2 respectively.

5. The regulating circuit for reducing input surge current of a switching power supply according to claim 1, characterized in that: The DCDC circuit includes a transformer and a MOS transistor Q3. The primary coil of the transformer is connected to the positive electrode of the capacitor C2 and the drain of the MOS transistor Q3 respectively.

6. The regulating circuit for reducing the input surge current of a switching power supply according to claim 5, characterized in that: The secondary coil of the transformer is output through the diode D4.

7. The regulating circuit for reducing input surge current of a switching power supply according to claim 5, characterized in that: The winding Nvcc of the power supply VCC is linearly coupled to the primary coil of the transformer.

8. The regulating circuit for reducing input surge current of a switching power supply according to claim 7, characterized in that: One end of the winding Nvcc is connected to the input end of the power supply VCC via the diode D3, and the other end of the winding Nvcc is connected to the source of the MOS transistor Q3.

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