CN205647256U - Soft -starting circuit - Google Patents

Abstract

The utility model discloses a soft start circuit, which comprises a flyback circuit, a soft start relay circuit, a PFC circuit, an LLC resonant circuit and an output circuit which are sequentially connected in series. The input terminal of the flyback circuit is connected to the LLC resonant circuit and the output circuit. Between the circuits, the output terminal of the flyback circuit is connected with the soft-start relay circuit. The utility model controls the on-off of the relay in the soft-start relay circuit through the DSP controller. The DSP controller detects the DC bus voltage of the PFC circuit. When the bus voltage of the PFC circuit rises to a high enough level, the DSP controller sends a signal to make the relay Pull in, short-circuit the soft-start resistor, so as to realize the safe and reliable soft-start of the high-power switching power supply, and make the circuit run safely and stably. It has the advantages of simple structure, stable and reliable operation.

Description

A soft start circuit

technical field

The utility model relates to a soft start circuit.

Background technique

Generally, the input circuit of switching power supply, that is, the PFC circuit, mostly adopts the capacitor filter at the output end, so when the input circuit is closed, a large instantaneous inrush current will be formed because the initial voltage on the capacitor is zero (as shown in Figure 1), especially For high-power switching power supply, its input adopts a large-capacity filter capacitor, and its inrush current can reach more than 100A. Such a large inrush current amplitude at the moment the power is turned on will often cause the input fuse to blow out, and sometimes even burn out the contacts of the closing switch, or even cause the air switch to fail to close. As a result, the switching power supply cannot be put into normal operation. For this reason, almost all switching power supplies will be equipped with a soft start circuit to prevent inrush current before their input circuit, so as to ensure the normal and reliable operation of the switching power supply.

Contents of the invention

In order to solve the above technical problems, the utility model provides a soft start circuit with simple structure and reliable operation.

The technical solution of the utility model to solve the above-mentioned problems is: a soft start circuit, including a flyback circuit and a soft start relay circuit, a PFC circuit, an LLC resonant circuit and an output circuit connected in series in sequence, and the input terminal of the flyback circuit is connected to Between the LLC resonant circuit and the output circuit, the output terminal of the flyback circuit is connected with the soft-start relay circuit.

In the above soft start circuit, the soft start relay circuit includes a DSP controller, two input AND gates, a first capacitor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, The seventh resistor, the first triode, the second triode, a relay, an optocoupler and the first diode, the input terminal of the DSP controller is connected to the PFC circuit, and the output terminal of the DSP controller is connected to the two inputs and One input terminal of the gate, the other input terminal of the two-input AND gate is connected to a high level, the output terminal of the two-input NAND gate is connected to the base of the second transistor through the seventh resistor, and the sixth resistor is connected to the first Between the base of the second transistor and the ground, the emitter of the second transistor is grounded, the collector of the second transistor is connected to a high level after passing through the fifth resistor and the fourth resistor, and the optocoupler includes A second diode and a third triode, the anode of the second diode is connected between the fifth resistor and the fourth resistor, the cathode of the second diode is connected to the collector of the second triode The electrodes are connected, the collector of the third transistor is connected to high level, the emitter of the third transistor is connected to the base of the first transistor through the third resistor, and the second resistor is connected to the base of the first transistor. Between the pole and the ground, the first capacitor is connected to both ends of the second resistor in parallel, the collector of the first triode is connected to a high level after passing through the coil of the relay, and the cathode of the first diode is connected to the first triode The collector of the tube, the anode of the first diode is connected to high level, the first resistor is connected to both ends of the normally open contact of the relay in parallel, and the two ends of the first resistor are used as the input and output ends of the soft-start relay circuit .

In the above soft-start circuit, the first diode is a common-cathode dual-switch diode.

The beneficial effects of the utility model are: the utility model controls the on-off of the relay in the soft-start relay circuit through the DSP controller, and the DSP controller detects the DC bus voltage of the PFC circuit. When the bus voltage of the PFC circuit rises to a high enough level, the DSP The controller sends out a signal to make the relay pull in and short-circuit the soft-start resistance, thereby realizing safe and reliable soft-start of the high-power switching power supply and making the circuit run safely and stably. It has the advantages of simple structure, stable and reliable operation.

Description of drawings

Figure 1 is a schematic diagram of the instantaneous inrush current generated when the switching power supply input circuit is switched on.

Fig. 2 is a structural block diagram of the utility model.

Fig. 3 is a circuit diagram of the soft-start relay circuit in Fig. 2 .

FIG. 4 is a circuit diagram of the LLC resonant circuit in FIG. 2 .

FIG. 5 is a circuit diagram of the flyback circuit in FIG. 2 .

detailed description

Below in conjunction with accompanying drawing and embodiment the utility model is described further.

As shown in Figure 2, the utility model includes a flyback circuit M4, a soft starting relay circuit, a PFC circuit M1, an LLC resonant circuit M2 and an output circuit M3, the soft starting relay circuit, a PFC circuit M1, an LLC resonant circuit M2 and an output The circuit M3 is sequentially connected in series, the input terminal of the flyback circuit M4 is connected between the LLC resonant circuit and the output circuit M3, and the output terminal of the flyback circuit M4 is connected with the soft-start relay circuit. U1, V1, W1 are three-phase input, Vout+, Vout- are the positive pole and negative pole of the DC output respectively, the Vout+ lead and GND are used as the input of the flyback circuit M4, and two DC power supply voltages +5V, +12V to power the soft-start relay circuit and other pull-up or bias circuits.

As shown in Figure 3, the soft-start relay circuit includes a DSP controller, a two-input AND gate Y, a first capacitor C1, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth Resistor R5, sixth resistor R6, seventh resistor R7, first triode S1, second triode S2, relay K, optocoupler D2 and common cathode double switch diode D1, the input end of the DSP controller Connect the PFC circuit, the output terminal of the DSP controller is connected to one input terminal of the two-input AND gate Y, the other input terminal of the two-input AND gate Y is connected to high level, and the output terminal of the two-input NAND gate is connected to the seventh resistor R7 The base of the second transistor S2, the sixth resistor R6 is connected between the base of the second transistor S2 and the ground, the emitter of the second transistor S2 is grounded, and the second transistor S2 The collector is connected to a high level after the fifth resistor R5 and the fourth resistor R4, and the optocoupler D2 includes a second diode and a third triode, and the anode of the second diode is connected to Between the fifth resistor R5 and the fourth resistor R4, the cathode of the second diode is connected to the collector of the second triode S2, the collector of the third triode is connected to high level, and the third triode The emitter is connected to the base of the first transistor S1 through the third resistor R3, the second resistor R2 is connected between the base of the first transistor S1 and the ground, and the first capacitor C1 is connected in parallel to the second resistor R2. terminal, the collector of the first triode S1 is connected to a high level after the coil of the relay K, the cathode of the common-cathode double-switching diode D1 is connected to the collector of the first triode S1, and the common-cathode double-switching diode D1 The anode is connected to a high level, the first resistor R1 is connected in parallel to both ends of the normally open contact of the relay K, and the two ends of the first resistor R1 are used as the input end and output end of the soft-start relay circuit.

The first resistor R1 is used as a soft-start resistor, the first capacitor C1 and the third resistor R3 form a low-pass filter to achieve the purpose of amplifying high-frequency interference; the second resistor R2 and the third resistor R3 are voltage divider resistors, when optically coupled When the device D2 is turned on, the +12V voltage is applied to the second resistor R2 and the third resistor R3, so that the base input voltage of the first triode S1 is 12*R2/(R2+R3), and the sixth resistor R6 and the third resistor R3 The seventh resistor R7 is a voltage divider resistor, so that the base input voltage of the second transistor S2 is AC RELAY*R6/R6*R7, when the second transistor S2 is turned on, +5V voltage is applied to the fourth resistor On R4 and the fifth resistor R5, the optocoupler D2 is connected in parallel at both ends of the fifth resistor R5 and conducts through resistor division. Y is a CMOS logic AND gate. When the DSP controller gives a signal, the logic AND gate Y is true, and outputs a high level to make the relay K close. The DSP controller detects the DC bus voltage of the PFC circuit M1. When the bus voltage of the PFC circuit M1 rises to a high enough level, the DSP controller sends a signal to make the relay K pull in and short-circuit the first resistor R1, thereby realizing the safety of the high-power switching power supply. Reliable soft start.

Figure 4 is the circuit diagram of the LLC resonant circuit M2, in which Q1, Q2, Q3, and Q4 are power MOSFETs, Lr is the resonant inductance, Cr is the resonant capacitor, Lm is the transformer leakage inductance, and T is the transformer.

Figure 5 is the circuit diagram of the flyback circuit. In the figure, Cin is a large electrolytic capacitor, Vz is a reverse breakdown diode, D41 is a diode, Q is a power MOSFET, T is a flyback transformer, D42 is a rectifier diode, and C41 is a chip capacitor. C42, C43, and C44 are large electrolytic capacitors, LM7812 is an output +12 voltage regulator, and LM7805 is an output +5V voltage regulator.

Claims (3)

1. a soft starting circuit, it is characterised in that: include circuit of reversed excitation and soft the relay circuit being sequentially connected in series, PFC electricity Road, LLC resonance circuit and output circuit, the input of described circuit of reversed excitation is connected between LLC resonance circuit and output circuit, instead The outfan of excitation circuit is connected with soft relay circuit.

Soft starting circuit the most according to claim 1, it is characterised in that: described soft relay circuit includes DSP control Device, two input with door, the first electric capacity, the first resistance, the second resistance, the 3rd resistance, the 4th resistance, the 5th resistance, the 6th resistance, 7th resistance, the first audion, the second audion, relay, photo-coupler and the first diode, described dsp controller defeated Entering and terminate pfc circuit, output termination two input of dsp controller and an input of door, another of two inputs and door is defeated Entering to terminate high level, the outfan of two input nand gates connects the base stage of the second audion through the 7th resistance, and described 6th resistance connects Between the base stage and ground of the second audion, the grounded emitter of the second audion, the colelctor electrode of the second audion is through the 5th electricity Resistance, the 4th resistance are followed by high level, and described photo-coupler includes second diode and the 3rd audion, and described second The anode of diode is connected between the 5th resistance and the 4th resistance, the negative electrode of the second diode and the colelctor electrode phase of the second audion Even, the colelctor electrode of the 3rd audion connects high level, and the emitter stage of the 3rd audion connects the base stage of the first audion through the 3rd resistance, Second resistance is connected between base stage and the ground of the first audion, and the first electric capacity is attempted by the second resistance two ends, the first audion Colelctor electrode is followed by high level through the coil of relay, and the negative electrode of described first diode connects the colelctor electrode of the first audion, and first The anode of diode connects high level, and described first resistance is attempted by the normally opened contact two ends of relay, the first resistance two ends conduct The input of soft relay circuit and outfan.

Soft starting circuit the most according to claim 2, it is characterised in that: described first diode is common cathode biswitch two Pole is managed.