CN219812079U

CN219812079U - Synchronous rectification flyback AC-DC conversion power supply

Info

Publication number: CN219812079U
Application number: CN202320929536.6U
Authority: CN
Inventors: 李闻达; 高宁
Original assignee: Shanghai Maritime University
Current assignee: Shanghai Maritime University
Priority date: 2023-04-23
Filing date: 2023-04-23
Publication date: 2023-10-10
Anticipated expiration: 2033-04-23

Abstract

The utility model relates to a synchronous rectification flyback AC-DC conversion power supply, which comprises a power supply input circuit, a flyback input and control circuit, a multi-output circuit containing synchronous rectification and a transformer, wherein the secondary side of the transformer is divided into three output windings, and each output winding is connected with one output circuit in the multi-output circuit containing synchronous rectification. Compared with the prior art, the utility model has the advantages of smooth and stable output voltage, low ripple noise, high precision and the like.

Description

Synchronous rectification flyback AC-DC conversion power supply

Technical Field

The utility model relates to the technical field of design and control of switching power supplies, in particular to a synchronous rectification flyback alternating current-direct current conversion power supply.

Background

In the field of electronic applications, flyback conversion power supplies are widely used in power supply design. The traditional flyback conversion circuit adopts diode rectification, but the diode rectification has the problems of conduction loss and reverse recovery, so the efficiency is lower. And the conventional flyback conversion circuit also has various problems such as large output ripple, serious electromagnetic interference and the like.

Disclosure of Invention

The utility model aims to overcome the defects of the prior art and provide a synchronous rectification flyback alternating current-direct current conversion power supply.

The aim of the utility model can be achieved by the following technical scheme:

the flyback AC-DC conversion power supply comprises a power input circuit, a flyback input and control circuit, a multi-output circuit containing synchronous rectification and a transformer, wherein the secondary side of the transformer is divided into three output windings, each output winding is connected with one output circuit containing the multi-output circuit containing the synchronous rectification, a first output winding of the secondary side of the transformer is connected with a drain electrode and a source electrode of a synchronous switching tube in series, a circuit consisting of a resistor, a resistor and a capacitor is connected between the drain electrode and the source electrode of the synchronous switching tube in parallel, one end of the first output winding and the source electrode of the synchronous switching tube are respectively connected with a first output anode and a first output cathode corresponding to the first output circuit, an electrolytic capacitor and an electrolytic capacitor are connected between the first output anode and the first output cathode, and a protection circuit, a filter circuit and a noise reduction voltage stabilizing circuit are also connected between the first output anode and the second output anode;

the input signal of the grid electrode of the synchronous switching tube is output by a driving pin DRV1 of the chip, a VCC1 pin of the chip is connected with a resistor in series to be connected with a first output positive electrode, a grounding pin Gnd1 of the chip is connected with a first output negative electrode, a capacitor and a capacitor are connected between the pin VCC1 and the pin Gnd1 in parallel, a programming resistor and a programming resistor are respectively connected with a Ton port and a Toff port of the chip in series, the resistor is connected between the pin DRV1 and the pin Gnd1 in parallel, and a current pin CS1 of the chip is connected with the first output negative electrode through the resistor.

Further, the structure of an output circuit connected with the other two output windings of the secondary side of the transformer is the same, the second output winding is connected with a diode, the diode is connected with a second output positive electrode, a second output negative electrode is grounded, and an electrolytic capacitor, a capacitor and a resistor are connected in parallel between the second output positive electrode and the second output negative electrode; the third output winding is connected with a diode, the diode is connected with a third output positive electrode, a third output negative electrode is grounded, and an electrolytic capacitor, a capacitor and a resistor are connected in parallel between the third output positive electrode and the third output negative electrode.

Further, the flyback input and control circuit is connected with the primary side of the transformer, the primary side comprises an input winding and a feedback winding, the flyback input and control circuit comprises a peak absorption circuit, a driving control circuit and a feedback circuit, the flyback input and control circuit is connected with the positive output end BUS+ and the negative output end BUS-of the power input circuit, the positive output end BUS+ is connected with the peak absorption circuit and the input winding of the transformer, and the peak absorption circuit consists of a diode, a diode and a resistor which are connected in series;

the drive control circuit comprises a chip, a diode and a resistor are connected in series with the positive pole of a feedback winding of the transformer, the resistor is connected with an input port VDD of the chip, the input port VDD is connected with a standby power supply V_AUX, a decoupling capacitor is connected in parallel between the input port VDD and a grounding end Gnd2 of the chip, the grounding end Gnd2 is connected with a negative pole output end BUS-, an electrolytic capacitor is connected in parallel between the standby power supply V_AUX and the grounding end Gnd2,

the driving pin DRV2 of the chip is connected with the current limiting resistor in series and is connected to the base level of the triode, the driving pin DRV2 is connected with the emitter of the triode in series, the collector of the triode is connected with the negative electrode output end BUS-, the emitter of the triode is connected with the grid electrode of the power switch tube, the resistor is connected between the grid electrode and the source electrode of the power switch tube in parallel, the drain electrode of the triode is connected with the output end of the peak absorption circuit, and the output end of the peak absorption circuit is also connected with the high-voltage input end HV of the chip.

Further, the feedback circuit is divided into a voltage feedback part and a current feedback part, the voltage feedback part comprises a voltage dividing resistor and a voltage dividing resistor which are connected in series with the positive pole of the feedback winding of the transformer, the midpoints of the voltage dividing resistor and the voltage dividing resistor are connected to a voltage pin VS of the chip, the source electrode of the power switch tube is connected in series with a sampling resistor, the other end of the sampling resistor is connected with a negative pole output end BUS-, and the source electrode of the power switch tube is connected in series with the resistor to a current pin CS of the chip.

Further, the input end of the power input circuit is an input socket, the input socket is connected with alternating current, a pin 1 of the input socket is connected with a phase line L, a pin 3 is connected with a neutral line N, the phase line L is connected with an onboard fuse, a piezoresistor is connected between the onboard fuse and the neutral line N in parallel, the onboard fuse is connected with a thermistor, a resistor and the resistor are connected in series and then connected between the phase line L and the neutral line N in parallel, a metal foil capacitor is also connected between the phase line L and the neutral line N in parallel, and the phase line L and the neutral line N connected with the metal foil capacitor in parallel are connected with a common mode inductor;

the common-mode inductor is connected with the full-bridge rectifying tube, the output of the full-bridge rectifying tube is connected with the inductor in series, and the output of the filtering circuit is connected with the positive output end BUS+ and the negative output end BUS-in parallel.

Further, the protection circuit with the first output anode and the first output cathode connected in parallel consists of a resistor, a resistor and a resistor which are connected in parallel.

Further, the filter circuit with the anode and cathode of the first output connected in parallel is an LC filter circuit, and the LC filter circuit is composed of a capacitor connected in parallel and an inductor connected in series.

Further, the noise reduction and voltage stabilization circuit with the first output anode and the first output cathode connected in parallel consists of a capacitor and a capacitor, and the capacitor are connected in parallel at two ends of the capacitor.

Further, the filter circuit with the parallel outputs of the full-bridge rectifier tube consists of a capacitor, a capacitor and an inductor connected between the capacitor and the capacitor in parallel.

Further, the negative output terminal BUS-and the output negative are grounded through the Y capacitor.

Compared with the prior art, the utility model has the following beneficial effects:

(1) The secondary side of the flyback transformer adopts synchronous rectification technology, so that the output voltage is smooth and stable, and the ripple noise is low; has a simpler circuit structure and higher power efficiency.

(2) The input part of the utility model provides an alternating current input interface, so that the circuit can directly generate a stable low-voltage direct current power supply in a commercial power environment; the output part adopts a multi-output port design, and the whole has better practicability.

(3) The utility model adopts a control chip with constant voltage and constant current and primary side regulating function to realize high-precision control with low power consumption.

(4) The primary side of the utility model comprises a feedback winding, adopts a primary side feedback mode, omits the traditional secondary side voltage regulation, omits an isolation device, a reference voltage source and a linear optocoupler device for signal coupling between two sides, which are required by secondary side sampling, reduces the complexity of a control circuit, reduces the implementation cost and reduces the power supply volume.

Drawings

FIG. 1 is an overall circuit diagram of the present utility model;

FIG. 2 is a schematic diagram of a system configuration of the power supply of the present utility model;

FIG. 3 is a diagram of a power input circuit of the present utility model;

FIG. 4 is a diagram showing waveforms of input and output of the power input circuit of the present utility model;

FIG. 5 is a circuit diagram of the flyback input and control circuit of the present utility model;

FIG. 6 is a circuit diagram of a multi-output circuit including synchronous rectification according to the present utility model;

FIG. 7 is a timing diagram of the flyback circuit of the present utility model operating in DCM discontinuous mode;

FIG. 8 is a timing diagram of the flyback circuit of the present utility model operating in CCM discontinuous mode;

FIG. 9 is a diagram of a port and anti-interference circuit of the present utility model;

in the figure, a transformer TR1, a synchronous switching tube Q1, a power switching tube Q2, a triode Q3, a thermistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a resistor R10, a resistor R11, a voltage dividing resistor R12, a programming resistor R13, a resistor R14, a resistor R15, a programming resistor R16, a resistor R17, a current limiting resistor R18, a resistor R19, a resistor R20, a voltage dividing resistor R21, a sampling resistor R22, a resistor R23, a capacitor C1, a capacitor C2, a capacitor C3, an electrolytic capacitor C4, an electrolytic capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, a capacitor C10, a capacitor C11, an electrolytic capacitor C12, a capacitor C13, an electrolytic capacitor C14, a decoupling capacitor C15, an electrolytic capacitor C16, a capacitor C17, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a diode D7, a U8, a U1, a full-bridge chip, a fuse, an inductor L1, a full-bridge, an inductor L1, a capacitor L1, a rectifier capacitor L, a capacitor L, and the like.

Detailed Description

The utility model will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present utility model, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present utility model is not limited to the following examples.

The utility model relates to an alternating current-direct current converter circuit based on flyback circuit topology and combined with synchronous rectification technology. The circuit comprises an input circuit with a rectification function, a flyback control circuit, a transformer and a multi-output circuit comprising synchronous rectification; the input port directly receives alternating voltage, and the alternating voltage is input into the transformer after rectification; the control circuit is connected in series with the primary winding of the transformer; the output circuit is coupled with a secondary side power winding of the transformer, and outputs the energy released by the transformer during the turn-off period of the switching tube to the direct current voltage with stable load at the output side through synchronous rectification.

The utility model adopts synchronous rectification technology, and aims at the alternating current output by the transformer, and the rectification of the voltage of the output end is realized in the conducting state in the switching conversion process, thereby achieving the power conversion of the circuit. The advantages of using synchronous rectification technology are as follows: the synchronous rectifying device has the characteristics of quick response time, low switching loss, high efficiency, low output ripple and the like. Meanwhile, the synchronous rectification technology can also work in a high-voltage and high-power environment, and the stability of output voltage is ensured. The patent designs an AC-DC power supply conversion device formed by complete multi-circuit modules, which ensures that the complexity of a circuit structure is lower on the basis of ensuring the stable power supply output function, and fully provides higher safety reliability and power supply efficiency. The power supply provided by the utility model can be used for laboratory tests or power supply of 12V electronic products, and can be used for directly converting alternating current commercial power into stable multi-output 12V direct current.

The overall circuit configuration of the present utility model is shown in fig. 1. The system structure diagram of the power supply is shown in fig. 2. The utility model comprises a power input circuit, a flyback input and control circuit, a multi-output circuit comprising synchronous rectification, a transformer, and an accessory port and an anti-interference circuit. The input port can directly receive the power frequency alternating voltage, and output direct current to the flyback circuit after full-bridge rectification; the control circuit is connected in series with the primary winding of the transformer; the output circuit is coupled with a secondary side power winding of the transformer, and the energy released by the transformer during the turn-off period of the switching tube is subjected to synchronous rectification to generate stable direct current voltage at the output side and can be output to a load; in addition to the synchronous rectified output ports described above, there are two conventional dc output ports rectified by diodes. The accessory circuit is mainly a circuit for reducing interference and a port connection.

1. Power input circuit

The circuit diagram of the power input circuit is shown in fig. 3. The main function of the power input circuit is to input external alternating current into a power supply through a port, and output direct current voltage after filtering and full-bridge rectification for the primary side of the flyback converter.

The connection and working principle of the power input circuit are as follows:

the power input circuit includes three circuit portions: the input protection and anti-interference circuit, the rectifying circuit and the output filter circuit.

1. The alternating current is connected with an input socket J1 of a power supply through an external cable, a pin 1 of the port is connected with a phase line L, and a pin 3 is connected with a neutral line N. The phase line is first connected in series with F1, F1 is an onboard fuse, and provides 1A of overcurrent protection for the power supply. R1 is a thermistor, and when the temperature is too high, the resistance is reduced, and the current is increased, thereby causing a protection operation of the circuit port. MOV1 is a piezoresistor connected in parallel between LN lines, and is rapidly conducted when overvoltage mutation occurs in the power grid, so as to protect the switching power supply from instantaneous overvoltage. R2/R3 are connected in parallel between LN lines, and play a safety role in limiting the current magnitude during short circuit/overload. CX1 is a metal foil capacitor for reducing high frequency interference signals. The common mode inductor L2 is used for filtering common mode noise signals on the power input line, so that the input alternating current is more stable. The design is used for improving the safety and the anti-interference capability of the power supply.

2. The input LN line is connected to the full-bridge rectifier BR1 after passing through the circuit, and the inside of the LN line is composed of four diodes. The secondary output can be led to the load during both positive and negative half cycles of the current by unidirectional conduction of the diode. The current is conducted by the lower left and upper right diodes in the positive half cycle, and the other two are conducted in the negative half cycle, so that BUS+ on the output side is always the positive electrode of direct current.

3. The output side is connected with L1 in series and C1/C2/C3 in parallel to form a filter circuit, so that the fluctuation of the output direct current voltage is weakened and more stable.

The input and output of the power input circuit are shown in fig. 4: the input alternating current is alternating voltage (waveform one of fig. 4), and is filtered and full-wave rectified to be direct current voltage (waveform two of fig. 4), and then is filtered to output relatively stable direct current (waveform three of fig. 4).

2. Flyback input and control circuit

The flyback input control circuit mainly aims to provide direct current of a power supply input circuit for the primary side of a transformer, drive and control a power switch tube of the flyback circuit by utilizing a constant voltage and constant current controller chip, and can be adjusted according to the output condition of a load side.

The circuit of the flyback input and control circuit is shown in fig. 5. The flyback input and control circuit comprises an input and peak absorbing circuit, a driving control circuit and a feedback circuit. The model of the chip U2 of the flyback input and control circuit is UCC28710D.

The connection and working principle of the flyback input and control circuit are as follows:

1. the input voltage of the transformer TR1 is introduced by bus+ of the power input circuit; the D1/D2/D3/D4 and R8 form an absorption protection circuit, wherein the transient voltage suppression diode and the resistor can absorb the current energy of transient overvoltage and convert the current energy into heat.

2. The driving control circuit consists of a chip U2 and a peripheral circuit; the feedback winding of the transformer is connected with a diode D5 and a resistor R14 in series and is connected to an input port VDD of U2 to provide power; the decoupling capacitor C15 is connected in parallel between the VDD and the GND and is used for reducing power supply noise; and simultaneously, V_AUX is led out from VDD and is used as an auxiliary power supply of a circuit system, and an electrolytic capacitor C14 is connected in parallel to GND to stabilize output voltage. The drive control circuit is connected with the output end of the protection circuit through the HV pin of the chip U2, the HV pin is a starting pin of the chip, and when the voltage of the HV pin is higher than the starting voltage, the chip can enter an operation mode.

3. The DRV driving pin of the control chip U2 is connected in series with a current limiting resistor R18 and is connected to a base stage B of the triode Q3; the DRV series diode D7 is connected to the emitter E of Q3; collector C of Q3 is connected to BUS-of the DC power supply. The emitter of Q3 is connected to the gate G of the power switch Q2. And a resistor R19 is connected between the G/S poles of the Q2 in parallel to provide fixed bias, so that MOS (metal oxide semiconductor) can be effectively turned off when a front-stage circuit is opened, and the charge of a junction capacitor Cgs can be rapidly released when MOS is turned off.

When the chip U2 outputs the PWM driving signal, the high level is amplified by the triode Q3 and is provided to the grid G of the switching tube Q2, so that the Q2 is conducted, and the on-off of the primary side input is controlled.

4. The feedback circuit is divided into a voltage part and a current part. The positive pole of the output feedback winding is connected with voltage dividing resistors R12 and R21 in series, and the midpoint of the resistor is connected to a VS pin of U2 to serve as feedback voltage. The source S of the switching transistor Q2 is connected in series with the sampling resistors R22 to GND, and connected in series with the CS pins of the resistors R20 to U2 as current detection sampling lines. The feedback sampling line should be as short as possible to reduce noise interference.

And 5.TP5,6 are signal test points for voltage and current sampling respectively.

3. Multiple output circuit including synchronous rectification

The secondary side of the flyback transformer is an output circuit and is divided into three output windings, wherein one output winding is connected with a synchronous rectifying device, and outputs 12V voltage after filtering, so that the flyback transformer is a main power output port; the other two are common diode rectifying circuits and serve as auxiliary output ports. Each group of output circuits comprises rectifying, filtering and protecting circuits. A circuit diagram of the multiple output circuit is shown in fig. 6. In the multi-output circuit with synchronous rectification, the model of the adopted chip U1 is NCP4303ADR2G.

The connection and operation principle of the multi-output circuit including synchronous rectification is as follows:

1. the first output winding of the secondary side of the transformer is connected with a synchronous rectifying device; the side of the auxiliary stage is connected with a D, S stage of the synchronous switching tube Q1 in series and is used for synchronous control of output. The circuit formed by R9/R10/C9 is connected in parallel with the DS end of the switching tube and is used for absorbing peak voltage at the moment of switching tube switching-off and buffering larger voltage stress. The electrolytic capacitors C4 and C5 are connected in parallel and are used for filtering out ripple waves of the output voltage. The resistor R5/R6/R7 is a protection circuit and is connected in parallel between the positive electrode and the negative electrode of the output. The peak current and explosion risk caused by sudden discharge of the capacitor can be prevented when the power supply is short-circuited; and can generate certain shunt to limit output when the output current is overlarge; the output voltage can be stabilized.

L3 and C6 form an LC filter circuit, are connected in parallel with C7/C8 and are connected in parallel between the positive electrode and the negative electrode of the output, and play a role in filtering, noise reduction and voltage stabilization of the output.

2. For the circuit of the synchronization control chip U1: the VCC pin is connected in series with R4 and is connected with the secondary side output positive electrode P12V to provide power supply for the chip. The GND pin of the chip is connected with the ground line P12V_GND of the first group output. The capacitors C10 and C11 are connected in parallel between VCC and GND and serve as decoupling capacitors for stably reducing the input voltage of the chip. R16 and R13 are respectively connected in series with Ton and Toff ports of the chip and used as programming resistors, and the on and off time of the synchronous switching tube is set according to the size of the resistors. The DRV pin output signal DRV_SR of the chip is connected to the synchronous switching tube Q1 for realizing the synchronous control function. The resistor R15 is connected in parallel between the DRV and the GND and is used as a current-limiting resistor protection circuit, and when faults such as short circuit and the like occur in the later stage, the resistor R15 generates a certain voltage drop and shunts to limit the maximum value of the output current. The TR/D and Comp pins of the chip are not used and should be connected to the negative pole P12V_GND. The CS pin of the chip is connected to GNDP12V of the circuit via resistor R11 for feedback of current sampling. The feedback line should be as short as possible to reduce signal noise interference.

3. The design of the additional two paths of output structures of the secondary side of the transformer is the same. The diodes D6 and D8 are output rectifying diodes, and when the primary side switch is turned off, the secondary side releases energy, and the diodes cut off the peak of the output voltage and limit the peak, so that the output is smooth direct current. The electrolytic capacitors C12 and C16 are energy storage filter capacitors, which can release energy when the primary side switch is turned on and have the function of filtering ripple waves. The capacitors C13, C17 are connected in parallel between the output 12V and ground for filtering the smoothed output voltage.

The supplementary working principle of the synchronous rectification part of the multi-output circuit is as follows:

(1) When the flyback circuit operates in DCM discontinuous mode, the timing is as shown in fig. 7. At time T1, the primary side power switching transistor Q2 Is turned off, the energy stored in the transformer TR1 Is transferred to the secondary side, the primary side current Ip decreases, and the secondary side current Is increases. Because of the delay of the synchronous rectification control chip of the secondary side, the DRV_SR is turned from low level to high level at the moment T2, and the synchronous rectification tube Q1 of the secondary side is controlled to be conducted. In the intermittent mode, drv_sr is turned from high to low at time T3, and the secondary synchronous rectifier Q1 is controlled to be turned off. At time T4, as the secondary side current Is decreases and reaches zero, the voltage vds_sr across the secondary side synchronous rectifier Q1 increases until the vds_sr reaches the plateau value Vin/n+vo at time T5. After that, the primary side of the transformer is opened again and stored with energy to the transformer, thereby operating in a reciprocating manner.

(2) When the flyback circuit operates in CCM discontinuous mode, the timing is as shown in fig. 8. At time T1, the primary side power switch tube driving signal vgs_sw is inverted to a low level, the control Q2 is turned off, and the energy stored in the transformer TR1 is transferred to the secondary side. The primary current Ip decreases and the secondary current Is increases. Because of the delay of the synchronous rectification control chip of the secondary side, the DRV_SR is turned from low level to high level at the moment T2, and the synchronous rectification tube Q1 of the secondary side is controlled to be conducted. Because of continuity, the secondary side current does not drop to the lowest point at the time T3, the energy is not completely released, the DRV_SR is turned from high level to low level, and the secondary side synchronous rectifier Q1 is controlled to be turned off. At time T4, as the primary current Ip is restored and rises, the voltage vds_sr across the secondary synchronous rectifier Q1 rises rapidly to and reaches the plateau value Vin/n+vo. And operates in a reciprocating manner.

4. Port and anti-interference circuit

The power supply of the present utility model has other peripheral circuits such as ports and anti-interference circuits in addition to the main circuit modules. The circuit diagram of the port and the anti-interference circuit is shown in fig. 9.

The connection and working principle of the port and the anti-interference circuit are as follows:

1. the output port of the power supply is divided into three connectors J2, J3 and J4. The 1/2 pin of J2 is connected with P12V output after synchronous rectification, and the 3/4 pin is connected with P12V_GND; the 1/2 pin of J3 is connected with 1SO_12V1, and the 3/4 pin is connected with GND2; the 1/2 pin of J4 is connected with 1SO_12V2, and the 3/4 pin is connected with GND2.

2. The power signal lines acl+2, ACN-2, p12v_gnd, GND2 are connected to the ground through Y capacitors CY1, CY2, CY5, CY6 for absorbing high frequency noise and stabilizing the quality of the output signal.

3. The primary side negative electrode BUS-is connected in series with power grounding P12V_GND, GND2 by capacitors CY3, CY 4. The primary side and the secondary side of the transformer have tiny parasitic capacitance, and common mode interference of a primary circuit of the switching power supply can be transmitted to a secondary circuit through the capacitance. Parasitic capacitance also exists between the secondary circuit and the ground, and common mode interference can flow back to the ground through the parasitic capacitance to form conductive disturbance to an external power supply network. A capacitance is added between the primary and secondary sides to reduce the energy of the common mode disturbance flowing from the secondary circuit into the ground.

The utility model has the following advantages:

(4) The control circuit of the flyback circuit adopts a primary side feedback mode, so that an isolation device, a reference voltage source and the like required by secondary side sampling are omitted, the complexity of the control circuit is reduced, and the implementation cost is reduced. Primary side feedback (Primary Side Regulation, PSR) on the primary side of a flyback transformer by detecting parameters of the primary or auxiliary windings of the transformer to achieve an output voltage U _O Or output current I _O Is controlled by the control system. The primary side feedback method can eliminate the conventional Secondary side voltage regulation (SecondarySide Regulation, SSR) and linear optocoupler (e.g., PC 817) for signal coupling between two sides. Also, components such as a voltage sampling circuit for secondary output, a reference voltage source (e.g., TL 431) and the like can be omitted, the peripheral control circuit is simplified, the cost is reduced, and the power supply volume can be reduced. Because of the thermosensitive property of the optocoupler element, the working temperature of the flyback converter can be properly increased after the optocoupler element is omitted, so that the primary side feedback control sampling form is widely applied in a charger with low output power and a driving power supply circuit.

The foregoing describes in detail preferred embodiments of the present utility model. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the utility model by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.

Claims

1. The flyback AC-DC conversion power supply is characterized by comprising a power input circuit, a flyback input and control circuit, a multi-output circuit containing synchronous rectification and a transformer, wherein the secondary side of the transformer (TR 1) is divided into three output windings, each output winding is connected with one output circuit containing the multi-output circuit of synchronous rectification, the first output winding of the secondary side of the transformer (TR 1) is connected with the drain electrode and the source electrode of a synchronous switching tube (Q1) in series, a circuit composed of a resistor (R9), a resistor (R10) and a capacitor (C9) is connected between the drain electrode and the source electrode of the synchronous switching tube (Q1) in parallel, one end of the first output winding and the source electrode of the synchronous switching tube (Q1) are respectively connected with the first output positive electrode and the negative electrode corresponding to the first output circuit, an electrolytic capacitor (C4) and an electrolytic capacitor (C5) are connected between the first output positive electrode and the negative electrode in parallel, and a voltage stabilizing circuit, a filtering circuit and a noise reducing circuit are also connected between the first output positive electrode and the negative electrode in parallel;

the input signal of the grid electrode of the synchronous switch tube (Q1) is output by a driving pin DRV1 of a chip (U1), a VCC1 pin series resistor (R4) of the chip (U1) is connected to a first output positive electrode, a grounding pin Gnd1 of the chip (U1) is connected with a first output negative electrode, a capacitor (C10) and a capacitor (C11) are connected between the pin VCC1 and the pin Gnd1 in parallel, a programming resistor (R16) and a programming resistor (R13) are respectively connected between a Ton port and a Toff port of the chip (U1) in series, a resistor (R15) is connected between the pin DRV1 and the pin Gnd1 in parallel, and a current pin CS1 of the chip (U1) is connected to the first output negative electrode through the resistor (R11).

2. The flyback ac-dc conversion power supply according to claim 1, characterized in that the output circuits connected to the other two output windings of the secondary side of the transformer (TR 1) are identical in structure, the second output winding is connected to a diode (D6), the diode (D6) is connected to the second output positive electrode, the second output negative electrode is grounded, and an electrolytic capacitor (C12), a capacitor (C13) and a resistor (R17) are connected in parallel between the second output positive electrode and the second output negative electrode; the third output winding is connected with a diode (D8), the diode (D8) is connected with a third output positive electrode, a third output negative electrode is grounded, and an electrolytic capacitor (C16), a capacitor (C17) and a resistor (R23) are connected in parallel between the third output positive electrode and the third output negative electrode.

3. A synchronous rectified flyback ac-dc conversion power supply according to claim 2, characterized in that the flyback input and control circuit is connected to the primary side of the transformer (TR 1), the primary side comprising an input winding and a feedback winding, the flyback input and control circuit comprising a spike absorbing circuit, a drive control circuit and a feedback circuit, the flyback input and control circuit being connected to the positive output bus+ and the negative output BUS-of the power input circuit, the positive output bus+ being connected to the spike absorbing circuit and the input winding of the transformer (TR 1), the spike absorbing circuit being composed of a diode (D1), a diode (D2), a diode (D3), a diode (D4) and a resistor (R8) connected in series;

the drive control circuit comprises a chip (U2), a diode (D5) and a resistor (R14) which are connected in series with the positive pole of a feedback winding of a transformer (TR 1), the resistor (R14) is connected with an input port VDD of the chip (U2), the input port VDD is connected with a standby power supply V_AUX, a decoupling capacitor (C15) is connected in parallel between the input port VDD and a grounding end Gnd2 of the chip (U2), the grounding end Gnd2 is connected with a negative pole output end BUS-, an electrolytic capacitor (C14) is connected in parallel between the standby power supply V_AUX and the grounding end Gnd2,

the driving pin DRV2 of the chip (U2) is connected with the current limiting resistor (R18) in series, the driving pin DRV2 is connected to the base level of the triode (Q3), the driving pin DRV2 is connected with the emitter of the triode (Q3) in series, the collector of the triode (Q3) is connected with the negative electrode output end BUS-, the emitter of the triode (Q3) is connected with the grid electrode of the power switch tube (Q2), the resistor (R19) is connected between the grid electrode and the source electrode of the power switch tube (Q2) in parallel, the drain electrode of the triode (Q3) is connected with the output end of the peak absorption circuit, and the output end of the peak absorption circuit is also connected with the high voltage input end HV of the chip (U2).

4. A synchronous rectified flyback ac-dc conversion power supply according to claim 3, characterized in that the feedback circuit is divided into two parts, namely a voltage feedback and a current feedback, the voltage feedback comprises a voltage dividing resistor (R12) and a voltage dividing resistor (R21) which are connected in series with the positive pole of the feedback winding of the transformer (TR 1), the midpoint of the voltage dividing resistor (R12) and the voltage dividing resistor (R21) is connected to the voltage pin VS of the chip (U2), the source electrode of the power switch tube (Q2) is connected in series with the sampling resistor (R22), the other end of the sampling resistor (R22) is connected with the negative pole output terminal BUS-, and the source electrode of the power switch tube (Q2) is connected in series with the resistor (R20) to the current pin CS of the chip (U2) at the same time.

5. The flyback ac-dc conversion power supply according to claim 1, wherein the input end of the power supply input circuit is an input socket (J1), the input socket (J1) is connected with ac, pin 1 of the input socket (J1) is connected with a phase line L, pin 3 is connected with a neutral line N, the phase line L is connected with an onboard fuse (F1), a varistor (MOV 1) is connected in parallel between the onboard fuse (F1) and the neutral line N, the onboard fuse (F1) is connected with a thermistor (R1), a resistor (R2) and a resistor (R3) are connected in series and then connected in parallel between the phase line L and the neutral line N, a metal foil capacitor (CX 1) is also connected in parallel between the phase line L and the neutral line N, and the phase line L and the neutral line N after connecting the metal foil capacitor (CX 1) in parallel are connected with a common mode inductor (L2);

the common-mode inductor (L2) is connected with the full-bridge rectifier tube (BR 1), the output of the full-bridge rectifier tube (BR 1) is connected with the inductor (L1) in series, and the output of the filter circuit is connected with the positive output end BUS+ and the negative output end BUS-in parallel.

6. The synchronous rectified flyback ac-dc conversion power supply according to claim 1, wherein the protection circuit having the first output connected in parallel with the positive and negative electrodes is composed of a resistor (R5), a resistor (R6) and a resistor (R7) connected in parallel with each other.

7. The synchronous rectified flyback ac-dc conversion power supply of claim 6 wherein the first output positive and negative electrode parallel filter circuit is an LC filter circuit comprising a capacitor (C6) and an inductor (L3) in series.

8. The synchronous rectified flyback ac-dc conversion power supply of claim 7 wherein the noise reduction and voltage stabilization circuit with the first output connected in parallel with the positive and negative electrodes is composed of a capacitor (C7) and a capacitor (C8), both the capacitor (C7) and the capacitor (C7) being connected in parallel with both ends of the capacitor (C6).

9. The synchronous rectified flyback ac-dc converter of claim 5 wherein the output parallel filter circuit of the full bridge rectifier tube (BR 1) is comprised of a capacitor (C1), a capacitor (C2), a capacitor (C3) and an inductor (L1) connected between the capacitor (C1) and the capacitor (C2) in parallel.

10. A synchronous rectified flyback ac-dc conversion power supply according to claim 2, wherein the negative output BUS-and the output negative are grounded via a Y capacitor.