CN204179959U - A kind of inverse-excitation type switch power-supply - Google Patents

Abstract

The utility model discloses a flyback switching power supply, which comprises an input circuit, a high-frequency conversion circuit, an output rectification filter circuit and a control circuit; the input end of the input circuit is connected to the mains, and the output end is connected to the high-frequency conversion circuit. input end; the input end of the output rectification filter circuit is connected to the output end of the high-frequency conversion circuit, and the output end of the output rectification filter circuit is the output end of the flyback switching power supply; the control circuit is connected to the high-frequency conversion circuit; the control circuit is also connected to the output end of the flyback switching power supply; The output terminal of the output rectification filter circuit is connected. The scheme has simple structure, low cost and high reliability, and is suitable for low-power and consumer electronic equipment, computer equipment, etc.

Description

A flyback switching power supply

technical field

The utility model relates to the field of power electronics, in particular to a flyback switching power supply.

Background technique

A switching power supply is a power supply in which the power electronic devices in the circuit work in a switching state. It belongs to the power source that exchanges electrical energy. It uses a power semiconductor device as a switch, and adjusts the output voltage by controlling the duty cycle of the switch.

Switching power supply must meet three conditions at the same time, namely: switch (the power electronic devices in the circuit work in a switch state instead of a linear state), high frequency (the power electronic devices in the circuit work in a high frequency instead of a low frequency close to the power frequency) and DC (power supply output is DC not AC). According to the current habits, switching power supply refers to the DC power supply in which power electronic devices work in high-frequency switching state. Therefore, switching power supply is often called high-frequency switching power supply.

The patent document with the application publication number CN102158093A published by the State Intellectual Property Office of the People's Republic of China on August 17, 2011, is a switching power supply, which includes an input electromagnetic interference filter, a rectifier filter circuit, a power conversion circuit, and a PWM control Circuit and output rectification and filtering circuit, the power conversion circuit includes power tube S1-4, capacitor C1-3, inductor Lk and diode D1-2; power tube S1 and power tube S3 in power tube S1-4 are connected in series to form super forearm , and anti-parallel diode D1-2, capacitor C1-3 for external absorption; power tube S2, power tube S4 form a lagging arm; output rectification filter circuit includes field effect transistor Sc, diode Da, diode Db, diode Dc and Capacitor Cc; field effect transistor Sc is connected in parallel with diode Dc, and then connected in series with capacitor Cc to form a frequency doubling circuit. This solution is a full-bridge type, with complex structure, high cost, low reliability, and problems of through and bias.

Contents of the invention

The utility model mainly solves the technical problems of complex structure, high cost and low reliability in the prior art, and provides a flyback switching power supply with simple structure, low cost and high reliability.

The utility model mainly solves the above-mentioned technical problems through the following technical solutions: a flyback switching power supply, including an input circuit, a high-frequency conversion circuit, an output rectification filter circuit and a control circuit; the input terminal of the input circuit Connect the mains, the output end is connected to the input end of the high-frequency conversion circuit; the input end of the output rectification filter circuit is connected to the output end of the high-frequency conversion circuit, and the output end of the output rectification filter circuit is the output end of the flyback switching power supply; The control circuit is connected with the high-frequency conversion circuit; the control circuit is also connected with the output terminal of the output rectification filter circuit.

Preferably, the input circuit includes a line filter circuit and a single-phase bridge rectifier circuit, and the line filter circuit includes a fuse FU1, a resistor R5, a capacitor C8, a capacitor C9, a capacitor C12, a capacitor C13 and a high-voltage low-pass filter LF, one end of the fuse FU1 is connected to the first pole of the commercial power, and the other end is connected to the first input terminal of the high-voltage low-pass filter LF; the second pole of the commercial power is connected to the second input terminal of the high-voltage low-pass filter LF; C8 is connected between the first input terminal and the second input terminal of the high-voltage low-pass filter LF; the resistor R5 is connected in parallel with the capacitor C8; the capacitor C9 is connected across the first output terminal and the second output of the high-voltage low-pass filter LF between the terminals; one end of the capacitor C12 is connected to the first output end of the high-voltage low-pass filter LF, and the other end is connected to the neutral point; one end of the capacitor C13 is connected to the second output end of the high-voltage low-pass filter LF, and the other end is connected to the neutral point; The single-phase bridge rectifier circuit includes a single-phase bridge rectifier D3, a capacitor C14 and a capacitor C15. The first input terminal of the single-phase bridge rectifier D3 is connected to the first output terminal of the high-voltage low-pass filter LF, and the second input terminal is connected to the high-voltage The second output end of the low-pass filter LF; one end of the capacitor C14 is connected to the negative pole of the output end of the single-phase bridge rectifier D3, and the other end is connected to the neutral point; one end of the capacitor C15 is connected to the positive pole of the output end of the single-phase bridge rectifier D3, and the other end Connect the neutral point; the negative pole of the output terminal of the single-phase bridge rectifier D3 is grounded.

Preferably, the high-frequency conversion circuit includes a transformer T1, a capacitor C3, a capacitor C17, a capacitor C19, a resistor R4, a resistor R11, a resistor R13, a resistor R15, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a diode D6, a diode D8, diode D11, diode D12 and transistor Q1; the first input terminal and the third input terminal of the transformer T1 are connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, the second input terminal is connected to the drain terminal of the transistor Q1, and the fourth input terminal terminal connected to the negative pole of diode D12; the positive pole of diode D12 is grounded; one end of capacitor C3 is connected to the positive pole of the output terminal of single-phase bridge rectifier D3, and the other end is connected to the negative pole of diode D6; resistor R4 is connected in parallel with capacitor C3; the positive pole of diode D6 is connected to transistor The drain of Q1; the gate of transistor Q1 is connected to the anode of diode D8 through resistor R11; the cathode of diode D8 is connected to the control circuit; the source of transistor Q1 is grounded through resistor R17; resistor R13 is connected in parallel with diode D8; one end of resistor R18 is connected to diode The negative pole of D8, the other end is connected to the first end of the capacitor C19 through the resistor R19; the second end of the capacitor C19 is grounded; the first end of the capacitor C19 is also connected to the control circuit; one end of the resistor R16 is connected to the source of the transistor Q1, and the other end Connect the first end of the capacitor C19; the anode of the diode D11 is grounded, and the cathode is connected to the gate of the transistor Q1; both the capacitor C17 and the resistor R15 are connected in parallel with the diode 11; the first input end and the second input end of the transformer T1 are the same coil The two terminals of the coil, the third input terminal and the fourth input terminal are two terminals of the same coil, and the output terminals are connected to the output rectifying and filtering circuit.

Preferably, the output rectification filter circuit includes a resistor R1, a resistor R2, a resistor R6, a resistor R9, a resistor R10, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C11, a capacitor C16, a diode D1, a diode D2, a diode D4, diode D5, inductor L1 and light-emitting diode LED1; the anode of the diode D1 is connected to the first output end of the transformer T1, and the cathode is connected to the first end of the inductor L1; the diode D2 is connected in parallel with the diode D1; one end of the resistor R1 is connected to the diode D1 The positive pole of the diode D1 is connected to the cathode of the diode D1 through the capacitor C1; the positive pole of the diode D4 is connected to the second output terminal of the transformer T1, and the negative pole is connected to the first terminal of the inductor L1; the diode D5 is connected in parallel with the diode D4; one end of the resistor R9 is connected to the diode D4 The positive pole of the diode D4, the other end is connected to the negative pole of the diode D4 through the capacitor C4; the second end of the inductor L1 is used as the positive output terminal of the flyback switching power supply; the positive pole of the diode D4 is used as the negative output terminal of the flyback switching power supply; the positive pole of the capacitor C5 Connect the second end of the inductor L1, the negative pole is connected to the positive pole of the diode D4; the capacitor C6, the capacitor C7 and the resistor R6 are all connected in parallel with the capacitor C5; the positive pole of the light-emitting diode LED1 is connected to the second end of the inductor L1 through the resistor R2, and the negative pole is connected to the diode D4 Positive pole; one end of the resistor R10 is connected to the third output terminal of the transformer T1, the other end is connected to the first terminal of the capacitor C11, and the second terminal of the capacitor C11 is used as the output terminal of the power supply VCC; the positive pole of the diode D7 is connected to the third output terminal of the transformer T1, The negative pole is connected to the power supply VCC; the positive pole of the capacitor C16 is connected to the power supply VCC, and the negative pole is grounded; the fourth output terminal of the transformer T1 is grounded; the first output terminal and the second output terminal of the transformer T1 are two terminals of the same coil, and the third output terminal and the fourth output terminal are two terminals of the same coil.

Preferably, the control circuit includes a current mode controller, capacitor C18, capacitor C20, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C25, capacitor C26, resistor R12, resistor R14, resistor R20, resistor R21, resistor R22, resistor R23, resistor R24, resistor R25, resistor R26, resistor R27, resistor R28, resistor R29, resistor R30, diode D9, diode D10, diode D13, diode D14, transistor Q3, transistor Q4, regulator Q2, light Coupler U1 and optocoupler U2; the current mode controller is UC3843; pin 7 of the current mode controller is connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, pin 7 is also connected to the power supply VCC, and pin 6 is connected to the diode D8 Pin 3 is connected to the first end of capacitor C19, pin 3 is also connected to the collector of transistor Q3, pin 1 is connected to the first output end of optocoupler U1, pin 2 and pin 5 are grounded, pin 4 is grounded through capacitor C25, and pin 8 The pins are connected to the emitter of the transistor Q3 and the emitter of the transistor Q4 at the same time; the positive poles of the capacitor C22 and the capacitor C23 are both connected to the power supply VCC, and the negative poles are both grounded; one end of the capacitor C24 is connected to the 8 pin of the current mode controller, and the other end is grounded; the resistor R28 Connected between pin 8 and pin 4 of the current mode controller; the base of the transistor Q3 is connected to the collector of the transistor Q4; the base of the transistor Q3 is also grounded through the resistor R30; the base of the transistor Q4 is connected to the optocoupler through the resistor R29 The second output terminal of U2; the second output terminal of optocoupler U1 is grounded; the first output terminal of optocoupler U2 is connected to the power supply VCC; the positive pole of capacitor C26 is connected to the second output terminal of optocoupler U2, and the negative pole is grounded; one end of resistor R26 is connected to The first output terminal of the optocoupler U1, and the other end is connected to the second output terminal of the optocoupler U2; the capacitor C21 is connected between the first output terminal and the second output terminal of the optocoupler U1; the resistor R27 is connected across the current mode control Between pin 8 and pin 1 of the controller; the cathode of diode D13 is connected to pin 8 of the current mode controller, and the anode is connected to the cathode of diode D14; the anode of diode D14 is connected to pin 1 of the current mode controller; resistor R25 is connected in parallel with diode D13; One end of the capacitor C20 is connected to the positive pole of the diode D13, and the other end is grounded; the negative pole of the diode D9 is connected to the positive output terminal of the flyback switching power supply, and the positive pole is connected to the first input terminal of the optocoupler U2 through the resistor R20; the negative pole of the diode D10 is connected to the flyback switching power supply. The positive output terminal of the switching power supply, the positive pole is connected to the first input terminal of the optocoupler U1 through the resistor R21; the resistor R23 is connected between the first input terminal and the second input terminal of the optocoupler U1; the reference pole of the voltage regulator Q2 is passed through The resistor R12 is connected to the positive output terminal of the flyback switching power supply, the anode is connected to the negative output terminal of the flyback switching power supply, and the cathode is connected to the second input terminal of the optocoupler U1; the resistor R24 and the capacitor C18 are connected in series to the voltage regulator Q2 Between the reference electrode and the cathode of the voltage regulator; after the resistor R14 and the resistor R22 are connected in series, they are connected across the reference electrode and the anode of the voltage regulator Q2 between.

Preferably, the incoming line filter circuit further includes a thermistor RTW1, and the thermistor RTW1 is connected in series between the second pole of the commercial power and the second input terminal of the high-voltage low-pass filter LF.

This program drives UC3843 through rectification and filtering, and makes it provide driving pulses to drive the switch tube to work. At the same time, through the detection of voltage, the output current signal is changed, and the conduction and cut-off of the switch tube are adjusted, so as to achieve the purpose of stabilizing the output voltage.

The beneficial effects brought by the utility model are that the cost is low, the structure is simple, the reliability is high and the application range is wide.

Description of drawings

Fig. 1 is a kind of structural diagram of the utility model;

Fig. 2 is a kind of circuit schematic diagram of the utility model;

In the figure: 1. Input circuit, 2. High-frequency conversion circuit, 3. Output rectification and filtering circuit, 4. Control circuit.

detailed description

The technical solutions of the present utility model will be further specifically described below through the embodiments and in conjunction with the accompanying drawings.

Embodiment: a kind of flyback switching power supply of this embodiment, as shown in Figure 1, comprises input circuit, high-frequency conversion circuit, output rectification filter circuit and control circuit; The terminal is connected to the input terminal of the high-frequency conversion circuit; the input terminal of the output rectification filter circuit is connected to the output terminal of the high-frequency conversion circuit, and the output terminal of the output rectification filter circuit is the output terminal of the flyback switching power supply; the control circuit is connected to the high-frequency Transformation circuit; the control circuit is also connected with the output terminal of the output rectification filter circuit.

Fig. 2 is a circuit schematic diagram of this embodiment.

The input circuit includes an incoming line filter circuit and a single-phase bridge rectifier circuit, and the incoming line filter circuit includes a fuse FU1, a resistor R5, a capacitor C8, a capacitor C9, a capacitor C12, a capacitor C13 and a high-voltage low-pass filter LF. One end of the fuse FU1 is connected to the first pole of the mains, and the other end is connected to the first input end of the high-voltage low-pass filter LF; the second pole of the mains is connected to the second input end of the high-voltage low-pass filter LF; capacitor C8 is connected across the high-voltage Between the first input terminal and the second input terminal of the low-pass filter LF; the resistor R5 is connected in parallel with the capacitor C8; the capacitor C9 is connected between the first output terminal and the second output terminal of the high-voltage low-pass filter LF; the capacitor One end of C12 is connected to the first output end of the high-voltage low-pass filter LF, and the other end is connected to the neutral point; one end of the capacitor C13 is connected to the second output end of the high-voltage low-pass filter LF, and the other end is connected to the neutral point; single-phase bridge rectification The circuit includes a single-phase bridge rectifier D3, a capacitor C14, and a capacitor C15. The first input terminal of the single-phase bridge rectifier D3 is connected to the first output terminal of the high-voltage low-pass filter LF, and the second input terminal is connected to the high-voltage low-pass filter LF. The second output end of the capacitor C14; one end of the capacitor C14 is connected to the negative pole of the output end of the single-phase bridge rectifier D3, and the other end is connected to the neutral point; one end of the capacitor C15 is connected to the positive pole of the output end of the single-phase bridge rectifier D3, and the other end is connected to the neutral point; The negative pole of the output terminal of the single-phase bridge rectifier D3 is grounded.

R5 is a discharge resistor (safety resistor), which is used to prevent the plug from being charged for a long time when the power cord is plugged and unplugged.

LF is a GL type high-voltage low-pass filter used to prevent power supply noise signals.

C8, C9, C12, C13 and LF form the EMI circuit. It prevents the electromagnetic interference pulse of the power supply itself from interfering with other electrical equipment on the public line through conduction or radiation. At the same time, it also prevents the electromagnetic pulse on the public line from interfering with the work of the power supply itself. C8 and C9 anti-series mode interference circuit are used to suppress normal noise; C12, C13 and LF form an anti-common mode interference circuit to suppress common mode noise interference. Their combined application has a strong attenuation bypass effect on electromagnetic interference. C14 and C15 are used as high frequency filter bypass.

The high frequency conversion circuit includes transformer T1, capacitor C3, capacitor C17, capacitor C19, resistor R4, resistor R11, resistor R13, resistor R15, resistor R16, resistor R17, resistor R18, resistor R19, diode D6, diode D8, diode D11, Diode D12 and transistor Q1; both the first input terminal and the third input terminal of the transformer T1 are connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, the second input terminal is connected to the drain terminal of the transistor Q1, and the fourth input terminal is connected to the diode D12 negative pole; the positive pole of the diode D12 is grounded; one end of the capacitor C3 is connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, and the other end is connected to the negative pole of the diode D6; the resistor R4 is connected in parallel with the capacitor C3; the positive pole of the diode D6 is connected to the drain of the transistor Q1; The gate of transistor Q1 is connected to the anode of diode D8 through resistor R11; the cathode of diode D8 is connected to the control circuit; the source of transistor Q1 is grounded through resistor R17; resistor R13 is connected in parallel with diode D8; one end of resistor R18 is connected to the cathode of diode D8, and the other is One end is connected to the first end of the capacitor C19 through the resistor R19; the second end of the capacitor C19 is grounded; the first end of the capacitor C19 is also connected to the control circuit; one end of the resistor R16 is connected to the source of the transistor Q1, and the other end is connected to the first end of the capacitor C19 One end; the anode of the diode D11 is grounded, and the cathode is connected to the gate of the transistor Q1; both the capacitor C17 and the resistor R15 are connected in parallel with the diode 11; the first input end and the second input end of the transformer T1 are two terminals of the same coil, The third input terminal and the fourth input terminal are two terminals of the same coil, and the output terminals are both connected to the output rectifying and filtering circuit.

The output rectification filter circuit includes resistor R1, resistor R2, resistor R6, resistor R9, resistor R10, capacitor C4, capacitor C5, capacitor C6, capacitor C7, capacitor C11, capacitor C16, diode D1, diode D2, diode D4, diode D5, Inductor L1 and light-emitting diode LED1; the anode of the diode D1 is connected to the first output end of the transformer T1, and the cathode is connected to the first end of the inductance L1; the diode D2 is connected in parallel with the diode D1; one end of the resistor R1 is connected to the anode of the diode D1, and the other end The cathode of the diode D1 is connected through the capacitor C1; the anode of the diode D4 is connected to the second output terminal of the transformer T1, and the cathode is connected to the first end of the inductor L1; the diode D5 is connected in parallel with the diode D4; one end of the resistor R9 is connected to the anode of the diode D4, and the other end The negative pole of the diode D4 is connected through the capacitor C4; the second end of the inductor L1 is used as the positive output end of the flyback switching power supply; the positive pole of the diode D4 is used as the negative output end of the flyback switching power supply; the positive pole of the capacitor C5 is connected to the first end of the inductor L1 Two terminals, the negative pole is connected to the positive pole of the diode D4; the capacitor C6, the capacitor C7 and the resistor R6 are all connected in parallel with the capacitor C5; the positive pole of the light-emitting diode LED1 is connected to the second end of the inductor L1 through the resistor R2, and the negative pole is connected to the positive pole of the diode D4; the resistor R10 One end is connected to the third output end of the transformer T1, the other end is connected to the first end of the capacitor C11, and the second end of the capacitor C11 is used as the output end of the power supply VCC; the positive pole of the diode D7 is connected to the third output end of the transformer T1, and the negative pole is connected to the power supply VCC; The positive pole of the capacitor C16 is connected to the power supply VCC, and the negative pole is grounded; the fourth output terminal of the transformer T1 is grounded; the first output terminal and the second output terminal of the transformer T1 are two terminals of the same coil, and the third output terminal and the fourth output terminal For the two terminals of the same coil.

The control circuit includes a current mode controller, capacitor C18, capacitor C20, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C25, capacitor C26, resistor R12, resistor R14, resistor R20, resistor R21, resistor R22, resistor R23, Resistor R24, resistor R25, resistor R26, resistor R27, resistor R28, resistor R29, resistor R30, diode D9, diode D10, diode D13, diode D14, transistor Q3, transistor Q4, voltage regulator Q2, optocoupler U1 and optocoupler U2 ; The current mode controller is UC3843; the 7 pins of the current mode controller are connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, the 7 pins are also connected to the power supply VCC, the 6 pins are connected to the negative pole of the diode D8, and the 3 pins Connect the first end of the capacitor C19, pin 3 is also connected to the collector of the transistor Q3, pin 1 is connected to the first output end of the optocoupler U1, pins 2 and 5 are grounded, pin 4 is grounded through the capacitor C25, and pin 8 is connected to the transistor Q3 at the same time The emitter of the transistor Q4 and the emitter of the transistor Q4; the positive poles of the capacitor C22 and the capacitor C23 are connected to the power supply VCC, and the negative poles are grounded; one end of the capacitor C24 is connected to the 8-pin of the current mode controller, and the other end is grounded; the resistor R28 is connected across the current mode Between pin 8 and pin 4 of the controller; the base of transistor Q3 is connected to the collector of transistor Q4; the base of transistor Q3 is grounded through resistor R30; the base of transistor Q4 is connected to the second output of optocoupler U2 through resistor R29 terminal; the second output terminal of the optocoupler U1 is grounded; the first output terminal of the optocoupler U2 is connected to the power supply VCC; the positive pole of the capacitor C26 is connected to the second output terminal of the optocoupler U2, and the negative pole is grounded; one end of the resistor R26 is connected to the first terminal of the optocoupler U1 One output terminal, the other end is connected to the second output terminal of the optocoupler U2; the capacitor C21 is connected between the first output terminal and the second output terminal of the optocoupler U1; the resistor R27 is connected across the pin 8 of the current mode controller and Between pin 1; the cathode of diode D13 is connected to pin 8 of the current mode controller, and the anode is connected to the cathode of diode D14; the anode of diode D14 is connected to pin 1 of the current mode controller; resistor R25 is connected in parallel with diode D13; one end of capacitor C20 is connected to the diode The positive pole of D13 and the other end are grounded; the negative pole of diode D9 is connected to the positive output terminal of the flyback switching power supply, and the positive pole is connected to the first input terminal of the optocoupler U2 through the resistor R20; the negative pole of diode D10 is connected to the positive output of the flyback switching power supply Terminal, the positive pole is connected to the first input terminal of the optocoupler U1 through the resistor R21; the resistor R23 is connected between the first input terminal and the second input terminal of the optocoupler U1; the reference pole of the voltage regulator Q2 is connected to the flyback through the resistor R12 The positive output terminal of the switching power supply, the anode is connected to the negative output terminal of the flyback switching power supply, and the cathode is connected to the second input terminal of the optocoupler U1; after the resistor R24 and the capacitor C18 are connected in series, they are connected across the reference pole and the cathode of the voltage regulator Q2 Between; after resistor R14 and resistor R22 are connected in series, they are connected between the reference electrode and the anode of the voltage stabilizing source Q2.

R28 and C25 are the setting resistance and capacitance of the switching frequency of UC3843, they determine the oscillation frequency and dead time.

R17 is an over-current detection resistor. If for some reason, the output terminal is short-circuited and over-current occurs, the drain current of the switch tube will increase significantly, the voltage at both ends of R11 will increase, and the voltage at pin 3 of UC3843 will also increase. When the voltage of this pin exceeds the normal value of 0.3V and reaches 1V (that is, the current exceeds 1.5A), the PWM comparator of UC3843 outputs a high level to reset the PWM latch and close the output. At this time, pin 6 of UC3843 has no output, and the MOS tube is cut off, thus protecting the circuit.

The zener diode D11 is connected to the 6-pin and the ground terminal of UC3843 to prevent the output voltage of the chip from being lower than the ground potential. R15 and C17 form a filter circuit.

Precision voltage regulator TL431 (Q2) and linear optocoupler PC817 (U1) constitute the feedback circuit. The TL431 adjustable precision voltage regulator is used to form an error voltage amplifier, and then the output is precisely adjusted through a linear optocoupler. R12, R14 and R22 are the external control resistors of the precision voltage regulator, R22 is adjustable, they determine the level of the output voltage, and form an external error amplifier together with TL431. When the output voltage rises, the sampling voltage VR21 also rises accordingly, and the set voltage is higher than the reference voltage (the reference voltage of TL431 is 2.5V), so that the output voltage of the error amplifier in TL431 rises, causing the on-chip drive triode The output voltage of the error amplifier decreases, and the output voltage VO decreases, and finally VO tends to be stable; on the contrary, the output voltage decreases and the setting voltage decreases. When the output voltage is lower than the setting voltage, the output voltage of the error amplifier decreases, and the on-chip driving transistor The output voltage rises, and finally the compensation input current of pin 1 of UC3843 changes accordingly, which prompts the on-chip PWM comparator to be adjusted to change the duty cycle to achieve the purpose of voltage regulation.

The regulator tube D10 and the resistor R21 form a voltage regulator protection circuit for the feedback optocoupler U1.

Voltage regulator tube D9, resistor R20, optocoupler U2, PNP transistor Q3, Q4 and other electronic components form an overvoltage protection circuit. When the output voltage is too high, D9 is broken down, which makes the optocoupler U2 act, and supplies voltage to the base of Q4. After turning on Q4, it turns on Q3, forcing pin 3 of UC3843 to present a high potential. At this time, UC3843 stops output, thus effectively protecting the switching power supply.

When the circuit is started, the integrated circuit is powered by R7, and after the circuit is started, it is powered by the self-contained bias power generated by a group of secondary windings of the transformer T1, that is, R10, D7, C11, and C16 form VCC to supply power to UC3843.

The incoming line filter circuit further includes a thermistor RTW1, which is connected in series between the second pole of the commercial power and the second input terminal of the high-voltage low-pass filter LF. The main function of the thermistor is to limit the instantaneous surge current in the power circuit, which can effectively reduce the excessive surge current, damage the input circuit, and avoid damage to the switch tube and oscillation circuit chip.

The specific embodiments described herein are only examples to illustrate the spirit of the present invention. Those skilled in the technical field to which the utility model belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, but they will not deviate from the spirit of the utility model or go beyond the appended claims defined range.

Although terms such as high-frequency conversion circuit and control circuit are frequently used in this paper, the possibility of using other terms is not excluded. These terms are only used to describe and explain the essence of the utility model more conveniently; interpreting them as any kind of additional limitation is contrary to the spirit of the utility model.

Claims (6)

1. A flyback switching power supply is characterized in that it comprises an input circuit, a high-frequency conversion circuit, an output rectification filter circuit and a control circuit; the input end of the input circuit is connected to the mains, and the output end is connected to the high-frequency conversion circuit Input terminal; the input terminal of the output rectification filter circuit is connected to the output terminal of the high frequency conversion circuit, and the output terminal of the output rectification filter circuit is the output terminal of the flyback switching power supply; the control circuit is connected to the high frequency conversion circuit; the control circuit is also connected with the output terminal of the flyback switching power supply; The output terminal of the output rectification filter circuit is connected. 2. A flyback switching power supply according to claim 1, wherein the input circuit includes an incoming line filter circuit and a single-phase bridge rectifier circuit, and the incoming line filter circuit includes a fuse FU1, a resistor R5, capacitor C8, capacitor C9, capacitor C12, capacitor C13 and high-voltage low-pass filter LF, one end of the fuse FU1 is connected to the first pole of the mains, and the other end is connected to the first input end of the high-voltage low-pass filter LF; The second pole of the electricity is connected to the second input end of the high-voltage low-pass filter LF; the capacitor C8 is connected between the first input end and the second input end of the high-voltage low-pass filter LF; the resistor R5 is connected in parallel with the capacitor C8; the capacitor C9 Connected across the first output terminal and the second output terminal of the high-voltage low-pass filter LF; one end of the capacitor C12 is connected to the first output end of the high-voltage low-pass filter LF, and the other end is connected to the neutral point; one end of the capacitor C13 is connected to the high voltage The second output end of the low-pass filter LF, and the other end is connected to the neutral point; the single-phase bridge rectifier circuit includes a single-phase bridge rectifier D3, capacitor C14 and capacitor C15, and the first input end of the single-phase bridge rectifier D3 is connected to The first output end of the high-voltage low-pass filter LF, and the second input end are connected to the second output end of the high-voltage low-pass filter LF; one end of the capacitor C14 is connected to the negative pole of the output end of the single-phase bridge rectifier D3, and the other end is connected to the neutral point ; One end of the capacitor C15 is connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, and the other end is connected to the neutral point; the negative pole of the output terminal of the single-phase bridge rectifier D3 is grounded. 3. A flyback switching power supply according to claim 2, wherein the high frequency conversion circuit includes a transformer T1, a capacitor C3, a capacitor C17, a capacitor C19, a resistor R4, a resistor R11, a resistor R13, a resistor R15, resistor R16, resistor R17, resistor R18, resistor R19, diode D6, diode D8, diode D11, diode D12 and transistor Q1; the first input terminal and the third input terminal of the transformer T1 are connected to the single-phase bridge rectifier D3 The positive pole of the output terminal, the second input terminal is connected to the drain of the transistor Q1, the fourth input terminal is connected to the negative pole of the diode D12; the positive pole of the diode D12 is grounded; one end of the capacitor C3 is connected to the positive pole of the output terminal of the single-phase bridge rectifier D3, and the other end is connected to The cathode of the diode D6; the resistor R4 is connected in parallel with the capacitor C3; the anode of the diode D6 is connected to the drain of the transistor Q1; the gate of the transistor Q1 is connected to the anode of the diode D8 through the resistor R11; the cathode of the diode D8 is connected to the control circuit; the source of the transistor Q1 The pole is grounded through resistor R17; resistor R13 is connected in parallel with diode D8; one end of resistor R18 is connected to the negative pole of diode D8, and the other end is connected to the first end of capacitor C19 through resistor R19; the second end of capacitor C19 is grounded; the first end of capacitor C19 is It is connected with the control circuit; one end of the resistor R16 is connected to the source of the transistor Q1, and the other end is connected to the first end of the capacitor C19; the anode of the diode D11 is connected to the ground, and the cathode is connected to the gate of the transistor Q1; both the capacitor C17 and the resistor R15 are connected to the diode’s 11 Parallel connection; the first input terminal and the second input terminal of the transformer T1 are two terminals of the same coil, the third input terminal and the fourth input terminal are two terminals of the same coil, and the output terminals are connected to the output rectification filter circuit . 4. A flyback switching power supply according to claim 3, wherein the output rectifying and filtering circuit includes a resistor R1, a resistor R2, a resistor R6, a resistor R9, a resistor R10, a capacitor C4, a capacitor C5, a capacitor C6, capacitor C7, capacitor C11, capacitor C16, diode D1, diode D2, diode D4, diode D5, inductor L1 and light-emitting diode LED1; the anode of the diode D1 is connected to the first output end of the transformer T1, and the cathode is connected to the inductor L1 The first end; the diode D2 is connected in parallel with the diode D1; one end of the resistor R1 is connected to the positive pole of the diode D1, and the other end is connected to the negative pole of the diode D1 through the capacitor C1; the positive pole of the diode D4 is connected to the second output terminal of the transformer T1, and the negative pole is connected to the inductor L1 The first end; the diode D5 is connected in parallel with the diode D4; one end of the resistor R9 is connected to the positive pole of the diode D4, and the other end is connected to the negative pole of the diode D4 through the capacitor C4; the second end of the inductor L1 is used as the positive output end of the flyback switching power supply; the diode The positive pole of D4 is used as the negative output terminal of the flyback switching power supply; the positive pole of capacitor C5 is connected to the second terminal of inductor L1, and the negative pole is connected to the positive pole of diode D4; capacitor C6, capacitor C7 and resistor R6 are all connected in parallel with capacitor C5; light-emitting diode LED1 The anode of the resistor R2 is connected to the second end of the inductor L1, and the cathode is connected to the anode of the diode D4; one end of the resistor R10 is connected to the third output end of the transformer T1, and the other end is connected to the first end of the capacitor C11, and the second end of the capacitor C11 serves as The output terminal of the power supply VCC; the positive pole of the diode D7 is connected to the third output terminal of the transformer T1, and the negative pole is connected to the power supply VCC; the positive pole of the capacitor C16 is connected to the power supply VCC, and the negative pole is grounded; the fourth output terminal of the transformer T1 is grounded; the first output terminal of the transformer T1 The second output end and the second output end are two terminals of the same coil, and the third output end and the fourth output end are two terminals of the same coil. 5. A flyback switching power supply according to claim 4, wherein the control circuit includes a current mode controller, capacitor C18, capacitor C20, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C25, capacitor C26, resistor R12, resistor R14, resistor R20, resistor R21, resistor R22, resistor R23, resistor R24, resistor R25, resistor R26, resistor R27, resistor R28, resistor R29, resistor R30, diode D9, diode D10, Diode D13, diode D14, transistor Q3, transistor Q4, voltage regulator Q2, optocoupler U1 and optocoupler U2; the current mode controller is UC3843; pin 7 of the current mode controller is connected to single-phase bridge rectifier D3 Pin 7 is also connected to the power supply VCC, pin 6 is connected to the negative pole of diode D8, pin 3 is connected to the first end of capacitor C19, pin 3 is also connected to the collector of transistor Q3, pin 1 is connected to the first terminal of optocoupler U1 Output terminal, pin 2 and pin 5 are grounded, pin 4 is grounded through capacitor C25, pin 8 is connected to the emitter of transistor Q3 and emitter of transistor Q4 at the same time; the positive poles of capacitor C22 and capacitor C23 are connected to the power supply VCC, and the negative poles are grounded; One end of C24 is connected to pin 8 of the current mode controller, and the other end is grounded; resistor R28 is connected between pin 8 and pin 4 of the current mode controller; the base of transistor Q3 is connected to the collector of transistor Q4; the base of transistor Q3 The pole is also grounded through the resistor R30; the base of the triode Q4 is connected to the second output terminal of the optocoupler U2 through the resistor R29; the second output terminal of the optocoupler U1 is grounded; the first output terminal of the optocoupler U2 is connected to the power supply VCC; the capacitor C26 The positive pole is connected to the second output end of the optocoupler U2, and the negative pole is grounded; one end of the resistor R26 is connected to the first output end of the optocoupler U1, and the other end is connected to the second output end of the optocoupler U2; the capacitor C21 is connected across the first output end of the optocoupler U1. Between the output terminal and the second output terminal; resistor R27 is connected between pin 8 and pin 1 of the current mode controller; the cathode of diode D13 is connected to pin 8 of the current mode controller, and the anode is connected to the cathode of diode D14; diode D14 The positive pole of the current mode controller is connected to pin 1 of the current mode controller; the resistor R25 is connected in parallel with the diode D13; one end of the capacitor C20 is connected to the positive pole of the diode D13, and the other end is grounded; the negative pole of the diode D9 is connected to the positive output terminal of the flyback switching power supply, and the positive pole passes through the resistor R20 Connect to the first input terminal of optocoupler U2; the cathode of diode D10 is connected to the positive output terminal of the flyback switching power supply, and the positive pole is connected to the first input terminal of optocoupler U1 through resistor R21; resistor R23 is connected across the first input terminal of optocoupler U1 Between the input terminal and the second input terminal; the reference electrode of the voltage regulator Q2 is connected to the positive output terminal of the flyback switching power supply through the resistor R12, the anode is connected to the negative output terminal of the flyback switching power supply, and the cathode is connected to the first terminal of the optocoupler U1 Two input terminals; the resistor R24 and the capacitor C18 are connected in series between the reference electrode and the cathode of the voltage regulator Q2; the resistor R14 and the resistor R After 22 is connected in series, it is connected between the reference electrode and the anode of the voltage stabilizing source Q2. 6. A flyback switching power supply according to claim 2 or 3 or 4 or 5, characterized in that the incoming line filter circuit further includes a thermistor RTW1, and the thermistor RTW1 is connected in series Between the second pole of electricity and the second input terminal of the high-voltage low-pass filter LF.