Load impedance self-adaptive flyback power supply circuit and implementation method thereof

Abstract

The invention provides a load impedance adaptive flyback power supply circuit and an implementation method thereof. The circuit comprises a filter circuit, a flyback power conversion circuit, an RCC auxiliary source power supply circuit, an output voltage and current acquisition and control circuit, a PWM pulse width modulation circuit and an isolation drive circuit. Impedance self-adaptive adjustment and constant-voltage and constant-current dual-output mode automatic switching can be carried out according to the working condition that the load impedance changes in a large range, and limited power output in a near impedance state is carried out through the primary side current overcurrent protection circuit, so that the voltage and current output requirement of the power supply in a full-load range is met. By using the circuit provided by the invention, bus current impact caused by load change can be reduced, the reliability and the safety of the circuit can be improved, and the circuit provided by the invention can be suitable for isolated DC-DC power conversion which has a large load impedance change range and respectively has constant voltage or constant current output requirements in different load states, and has better applicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of flyback power supply circuits, and in particular relates to a load impedance adaptive flyback power supply circuit and an implementation method thereof. Background Art

[0002] At present, the commonly used flyback power supply is generally a single constant voltage output mode. When its load impedance decreases and the output current increases, since the output voltage remains unchanged, its output power increases with the increase of output current. For a flyback power supply without primary overcurrent protection function, when its output power exceeds the maximum output capacity of the power supply, the power supply may burn out due to overpower; for a flyback power supply with primary overcurrent protection function, when its output power is too large and the primary current of the converter exceeds its overcurrent protection threshold, the output drive duty cycle of the power supply's PWM controller decreases, and the power supply output voltage decreases. At this time, the output voltage and current fluctuate with the load impedance, and the output of the power supply is uncontrolled. Therefore, in summary, the current flyback power supply is not suitable for working conditions with a large range of load impedance changes, and the output mode cannot be adjusted according to the actual load changes, and cannot meet the use requirements of a wide load range and dual output mode. Summary of the invention

[0003] The present invention provides a load impedance adaptive flyback power supply circuit and an implementation method thereof, aiming to solve the problem that the current flyback power supply is not suitable for working conditions with a large load impedance variation range, cannot adjust the output mode according to the actual load variation, and cannot meet the requirements of wide load range and dual output mode use.

[0004] In order to achieve the above object, the present invention adopts the following technical scheme: The present invention provides a load impedance adaptive flyback power supply circuit, which includes a filter circuit, a flyback power conversion circuit, an RCC auxiliary source power supply circuit, an output voltage and current acquisition and control circuit, a PWM pulse width modulation circuit and an isolation drive circuit; wherein: The input bus is filtered by the filtering circuit to supply power to the flyback power conversion circuit and the RCC auxiliary source power supply circuit; the flyback power conversion circuit provides voltage and current to the power load after completing the isolation conversion, and sends its output voltage and current acquisition signal to the output voltage and current acquisition and control circuit, and sends the primary current acquisition signal IS to the PWM pulse width modulation circuit; The RCC auxiliary source power supply circuit is used to: provide voltage and current for the output voltage and current acquisition and control circuit and the PWM pulse width modulation circuit through isolation conversion; The output voltage and current acquisition and control circuit is used to: form a voltage and current loop feedback signal FFK based on the power supply output voltage and current acquisition signal; The PWM pulse width modulation circuit is used to: perform power supply slow start, primary side overcurrent protection, current slope compensation and PWM pulse width adjustment based on the primary current acquisition signal IS and the voltage and current loop feedback signal FFK, and output the PWM drive signal to the isolation drive circuit; The isolation drive circuit is used to: output the MOS tube drive signal based on the PWM drive signal, realize the isolation of the primary and secondary ground lines, and control the on and off of the primary power MOS tube in the flyback power conversion circuit.

[0005] In some embodiments, the filter circuit includes a common-mode filter circuit and a differential-mode filter circuit, and the common-mode filter circuit and the differential-mode filter circuit are used to eliminate common-mode and differential-mode interference between the bus and the internal circuit of the power supply.

[0006] In some implementations, the flyback power conversion circuit is a main power conversion circuit of a flyback power supply, and the flyback power conversion circuit is used to complete isolation conversion through a flyback DC-DC converter.

[0007] Furthermore, the flyback power conversion circuit: collects the primary current through the current transformer, and sends the primary current collection signal IS to the PWM pulse width modulation circuit; receives the output drive signal from the isolation drive circuit to realize the switch control and duty cycle adjustment of the primary power MOS tube.

[0008] In some embodiments, the PWM pulse width modulation circuit includes a single-ended drive controller and its peripheral circuits, receives a primary current acquisition signal IS and a voltage-current loop feedback signal FFK, and outputs a PWM drive signal.

[0009] In some embodiments, the RCC auxiliary source power supply circuit includes a high-frequency self-excited magnetic isolation RCC circuit, and the RCC auxiliary source power supply circuit achieves magnetic isolation and voltage stabilization output by self-excited driving.

[0010] In some embodiments, the output voltage and current acquisition and control circuit includes an output voltage acquisition circuit, an output voltage PID negative feedback control circuit, an output current acquisition circuit, an output current PID negative feedback control circuit, and a feedback signal comparison circuit.

[0011] Furthermore, the output voltage and current acquisition and control circuit performs differential amplification processing on the received power supply output voltage and current acquisition signal, and compares the processed signal with the threshold voltage of the PID negative feedback control circuit to form a voltage and current loop feedback signal FFK, which is sent to the PWM pulse width modulation circuit.

[0012] In some embodiments, the isolation drive circuit isolates and transforms the PWM drive signal into a MOS tube drive signal, and sends it to the primary power MOS tube in the flyback power conversion circuit to control the MOS tube switch; by adjusting the output side drive resistance in the isolation drive circuit, the rising and falling edge waveforms of the MOS tube drive signal are adjusted, thereby adjusting the on-off speed of the MOS tube.

[0013] The present invention also provides a method for implementing a load impedance adaptive flyback power supply circuit, comprising the following steps: S1, filter the input bus to obtain a filtered input signal; perform power conversion on the filtered input signal to provide voltage and current for the power load, and collect the primary current collection signal IS; S2, RCC auxiliary source power supply circuit provides voltage and current for output voltage and current acquisition and control circuit and PWM pulse width modulation circuit; output voltage and current acquisition and control circuit performs differential amplification processing on output voltage and current acquisition signals, and forms voltage and current loop feedback signal FFK after loop operation; S3, PWM pulse width modulation circuit realizes power supply slow start, primary side overcurrent protection, current slope compensation and PWM pulse width adjustment based on primary current acquisition signal IS and voltage current loop feedback signal FFK, and generates PWM drive signal; S4. The isolation drive circuit outputs a MOS tube drive signal based on the PWM drive signal to achieve isolation of the primary and secondary ground lines, and controls the on and off of the primary power MOS tube in the flyback power conversion circuit, so that the flyback power supply can output voltage and current within the full load range.

[0014] Compared with the prior art, the load impedance adaptive flyback power supply circuit and its implementation method of the present invention have the following beneficial effects: The present invention discloses a load impedance adaptive flyback power supply circuit, which includes a filter circuit, a flyback power conversion circuit, an RCC auxiliary source power supply circuit, an output voltage and current acquisition and control circuit, a PWM pulse width modulation circuit and an isolation drive circuit; wherein: the input bus is filtered by the filter circuit to supply power to the flyback power conversion circuit and the RCC auxiliary source power supply circuit; the flyback power conversion circuit provides voltage and current to the power load after completing isolation conversion, and sends its output voltage and current acquisition signal to the output voltage and current acquisition and control circuit, and sends the primary current acquisition signal IS to the PWM pulse width modulation circuit; the RCC auxiliary source power supply circuit is used to: provide output voltage and current acquisition signal to the output voltage and current acquisition and control circuit through isolation conversion; The output voltage and current acquisition and control circuit and the PWM pulse width modulation circuit provide voltage and current; the output voltage and current acquisition and control circuit is used to: form a voltage and current loop feedback signal FFK based on the power supply output voltage and current acquisition signal; the PWM pulse width modulation circuit is used to: perform power supply slow start, primary side overcurrent protection, current slope compensation and PWM pulse width adjustment based on the primary side current acquisition signal IS and the voltage and current loop feedback signal FFK, and output the PWM drive signal to the isolation drive circuit; the isolation drive circuit is used to: output the MOS tube drive signal based on the PWM drive signal, realize the isolation of the primary and secondary side ground wires, and control the opening and closing of the primary side power MOS tube in the flyback power conversion circuit. Based on the above, the present invention is suitable for working conditions where the load impedance changes over a wide range, and can perform impedance adaptive adjustment, automatic switching of constant voltage and constant current dual output modes, and perform power limiting output under the state of adjacent impedance through the primary side current overcurrent protection circuit, thereby meeting the voltage and current output requirements of the power supply within the full load range. In addition, the use of this circuit can reduce the bus current impact caused by load changes, protect the primary input bus, and improve the overall reliability and safety of the working system.

[0015] The present invention realizes the automatic switching of constant voltage and constant current dual-mode output through a single topology, integrates the voltage source and current source functions, reduces the number of components used, improves the power density and reliability of the power supply, controls the production cost of the power supply, and has high economic value. In addition, the present invention has good functional expansibility, and can carry out the expansion design of the functions of power supply output voltage and current telemetry, output voltage and current remote control, etc. according to the needs on the basis of the present invention, thereby optimizing the function of the product, and having better practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings in the specification are used to provide further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0017] Figure 1 A schematic diagram of the overall architecture of a load impedance adaptive flyback power supply circuit and an implementation method thereof of the present invention; Figure 2 A schematic diagram of the principle of a filter circuit in a load impedance adaptive flyback power supply circuit and an implementation method thereof of the present invention; Figure 3 A schematic diagram of the principle of a flyback power conversion circuit in a load impedance adaptive flyback power supply circuit and an implementation method thereof of the present invention; Figure 4 It is a schematic diagram of the principle of an RCC auxiliary source power supply circuit in a load impedance adaptive flyback power supply circuit and an implementation method thereof of the present invention; Figure 5 It is a schematic diagram of the principle of an output voltage and current acquisition and control circuit in a load impedance adaptive flyback power supply circuit and an implementation method thereof of the present invention; Figure 6 It is a schematic diagram of the principle of a PWM pulse width modulation circuit in a load impedance adaptive flyback power supply circuit and an implementation method thereof of the present invention; Figure 7 The present invention is a schematic diagram of the principle of an isolation driving circuit in a load impedance adaptive flyback power supply circuit and an implementation method thereof. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0021] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0022] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] like Figure 1 As shown, the present invention provides a load impedance adaptive flyback power supply circuit, the circuit includes a filter circuit, a flyback power conversion circuit, an RCC auxiliary source power supply circuit, an output voltage and current acquisition and control circuit, a PWM pulse width modulation circuit and an isolation drive circuit; wherein: The input bus is filtered by the filtering circuit to supply power to the flyback power conversion circuit and the RCC auxiliary source power supply circuit; the flyback power conversion circuit provides voltage and current to the power load after completing the isolation conversion, and sends its output voltage and current acquisition signal to the output voltage and current acquisition and control circuit, and sends the primary current acquisition signal IS to the PWM pulse width modulation circuit; The RCC auxiliary source power supply circuit is used to: provide voltage and current for the output voltage and current acquisition and control circuit and the PWM pulse width modulation circuit through isolation conversion; The output voltage and current acquisition and control circuit is used to: form a voltage and current loop feedback signal FFK based on the power supply output voltage and current acquisition signal; The PWM pulse width modulation circuit is used to: perform power supply slow start, primary side overcurrent protection, current slope compensation and PWM pulse width adjustment based on the primary current acquisition signal IS and the voltage and current loop feedback signal FFK, and output the PWM drive signal to the isolation drive circuit; The isolation drive circuit is used to: output the MOS tube drive signal based on the PWM drive signal, realize the isolation of the primary and secondary ground lines, and control the on and off of the primary power MOS tube in the flyback power conversion circuit.

[0025] The present invention realizes adaptive adjustment of the flyback power supply output to the load impedance by real-time acquisition of the power supply output voltage and current signals, and feeds back to the PWM pulse width modulation circuit for dynamic adjustment, thereby ensuring the stable output of the flyback power supply under different load conditions. The flyback power conversion circuit provides voltage and current to the power load through isolation conversion, thereby improving the conversion efficiency. The RCC auxiliary source power supply circuit realizes magnetic isolation and voltage stabilization output, thereby reducing energy loss. The present invention can realize stable output of voltage and current within the full load range by comprehensively applying output voltage and current acquisition, PID negative feedback control, PWM pulse width modulation and isolation drive, etc., and has better applicability.

[0026] The functions of each circuit in the present invention are further described below: Filter circuit: It consists of common mode filter circuit and differential mode filter circuit. The common mode filter circuit and differential mode filter circuit eliminate the common mode and differential mode interference between the bus and the internal circuit of the power supply, so that the power supply has good electromagnetic compatibility characteristics; Flyback power conversion circuit: This circuit is the main power conversion circuit of the flyback power supply. The input bus is filtered by the filter circuit to power the circuit. The flyback DC-DC converter completes the isolation conversion to provide the power load with the voltage and current required for operation. The circuit collects the primary current through the current transformer, and sends the primary current collection signal IS to the PWM pulse width modulation circuit to realize the primary overcurrent protection function and limit the maximum output power of the power supply. The primary power MOS tube of this circuit receives the output drive signal from the isolation drive circuit to realize switch control and duty cycle adjustment. The output side of the circuit collects the output voltage and output current signals, and sends the output voltage and current collection signals to the output voltage and current collection and control circuit; RCC auxiliary power supply circuit: The auxiliary power supply circuit adopts high-frequency self-excited isolation RCC circuit, which has high power density and small size. The input bus is filtered by the filter circuit to supply power to the circuit, and the output voltage and current acquisition and control circuit and PWM pulse width modulation circuit are provided with the required voltage and current through isolation transformation; Output voltage and current acquisition and control circuit: This circuit receives the output voltage and current acquisition signals from the flyback power conversion circuit, completes the signal acquisition and processing through the differential amplifier circuit, and compares the processed signal with the threshold voltage of the PID negative feedback control circuit to form a voltage loop feedback signal and a current loop feedback signal. The two feedback signals are compared and the lower voltage is taken as the signal of the COMP terminal (the output terminal of the internal error amplifier) ​​of the PWM controller in the PWM pulse width modulation circuit; PWM pulse width modulation circuit: This circuit is based on a single-ended drive controller (in actual working conditions, the single-ended drive controller can be selected but not limited to UC1843), receives the primary current acquisition signal IS from the flyback power conversion circuit and the feedback signal FFK from the output voltage and current acquisition and control circuit, and realizes the functions of power supply slow start-up, primary overcurrent protection, current slope compensation, PWM pulse width adjustment, etc. through its peripheral circuit, and sends its output PWM drive signal to the isolation drive circuit; Isolation drive circuit: This circuit receives the PWM drive signal from the PWM pulse width modulation circuit, and realizes the isolation of the primary and secondary ground lines by driving the transformer. Its output drive signal is sent to the primary power MOS tube in the flyback power conversion circuit to control the MOS tube switch.

[0027] The circuit structure and working mechanism of a load impedance adaptive flyback power supply circuit and its implementation method of the present invention are analyzed below in conjunction with the accompanying drawings.

[0028] like Figure 2 As shown, the filter circuit is composed of a common-mode filter circuit and a differential-mode filter circuit. The common-mode filter circuit is composed of a common-mode filter inductor L1 and capacitors C1-C6, wherein pin 1 of the common-mode filter inductor L1 is connected to the bus positive line Vin+, pin 2 of the common-mode filter inductor L1 is connected to one end of the differential-mode filter inductor L2, pin 3 of the common-mode filter inductor L1 is connected to the bus return line VinGnd, pin 4 of the common-mode filter inductor L1 is connected to the power supply return line VinGnd2 of the subsequent power circuit, pins 1 and 3 of the common-mode filter inductor L1 are the same-named ends, and pins 2 and 4 are the same-named ends. One end of the filter capacitor C1 is connected to pin 1 of the common-mode filter inductor L1; the other end is connected to filter capacitors C2 and C3, the other end of the filter capacitor C2 is connected to pin 3 of the common-mode filter inductor L1, and the other end of the filter capacitor C3 is connected to the shell ground. One end of the filter capacitor C5 is connected to pin 2 of the common-mode filter inductor L1, and the other end is connected to filter capacitors C4 and C6. The other end of the filter capacitor C6 is connected to pin 4 of the common-mode filter inductor L1, and the other end of the filter capacitor C4 is connected to the shell ground.

[0029] The π-type differential mode filter circuit is composed of differential mode filter inductor L2 and capacitors C7 and C8. One end of the differential mode filter inductor L2 is connected to pin 2 of the common mode filter inductor L1, and the other end is connected to the positive power supply line Vin2+ of the subsequent power circuit. One end of the filter capacitor C7 is connected to pin 2 of the common mode filter inductor L1, and the other end is connected to the power supply return line VinGnd2 of the subsequent power circuit. One end of the filter capacitor C8 is connected to the positive power supply line Vin2+ of the subsequent power circuit, and the other end is connected to the power supply return line VinGnd2 of the subsequent power circuit.

[0030] The common-mode filter circuit and the differential-mode filter circuit are used to eliminate the common-mode and differential-mode interference between the bus and the internal circuit of the power supply, so that the power supply has good electromagnetic compatibility characteristics. The values ​​of the filter inductance and capacitance are determined according to the actual working conditions.

[0031] like Figure 3 As shown, the flyback power conversion circuit consists of a primary current acquisition circuit, an RCD voltage spike absorption circuit, a flyback power transformer T1, a power MOS tube Q1 and its gate-source parallel resistor R4, an output rectifier diode V1, an output filter capacitor C9, an output current sampling resistor R2 and its parallel filter capacitor C13, and an output voltage sampling filter capacitor C11.

[0032] Among them, the primary current acquisition circuit is composed of a current transformer L3, a magnetic reset resistor R3, a filter capacitor C12 and a signal output diode V3. Pin 1 of the current transformer L3 is connected to the positive power supply line Vin2+ of the power circuit, pin 2 of the current transformer L3 is connected to pin 1 of the flyback power transformer T1, pin 3 of the current transformer L3 is connected to the anode of the signal output diode V3, and pin 4 of the current transformer L3 is connected to the auxiliary source power supply loop CGnd. Pins 1 and 3 of the current transformer L3 are the same-name terminals, and pins 2 and 4 are the same-name terminals. After the magnetic reset resistor R3 is connected in parallel with the filter capacitor C12, one end is connected to pin 3 of the current transformer L3, and the other end is connected to pin 4 of the current transformer L3. The anode of the signal output diode V3 is connected to pin 3 of the current transformer L3, and the cathode is connected to the CS terminal (current detection terminal) of the PWM controller in the PWM pulse width modulation circuit.

[0033] The primary current acquisition circuit acquires the primary current through the current transformer L3, and sends the primary current acquisition signal IS to the PWM pulse width modulation circuit, thereby realizing primary overcurrent protection. The function of the magnetic reset resistor R3 is to perform magnetic reset of the current transformer when the primary current returns to zero, so as to avoid magnetic saturation of the current transformer.

[0034] The RCD voltage spike absorption circuit in the flyback power conversion circuit is composed of an absorption resistor R1, an absorption capacitor C10 and a diode V2. After the absorption resistor R1 is connected in parallel with the absorption capacitor C10, one end is connected to the 1st pin of the flyback power transformer T1, and the other end is connected to the cathode of the diode V2. The anode of the diode V2 is connected to the 2nd pin of the flyback power transformer T1. The function of the RCD voltage spike absorption circuit is to absorb the drain-source voltage spike when the power MOS tube Q1 is turned off, so as to avoid excessive voltage stress when the power MOS tube is turned off.

[0035] The drain of the power MOS tube Q1 in the flyback power conversion circuit is connected to the 2nd pin of the flyback power transformer T1, the source is connected to the power circuit power supply return line VinGnd2, and the gate is connected to the output Vgs+ end of the isolation drive circuit. One end of its gate-source parallel resistor R4 is connected to the gate of the MOS tube Q1, and the other end is connected to the source of the MOS tube Q1. The 3rd pin of the flyback power transformer T1 is connected to the anode of the output rectifier diode V1, and the 4th pin is connected to one end of the output filter capacitor C9. Its 1st pin and 4th pin are the same-named terminals, and the 2nd pin and 3th pin are the same-named terminals. The cathode of the output rectifier diode V1 is connected to the other end of the output filter capacitor C9, that is, the output power supply positive terminal Vout+ of the power supply. After the output current sampling resistor R2 and its parallel filter capacitor C13 are connected in parallel, one end is connected to the 4th pin of the flyback power transformer T1, and the other end is connected to the output power supply ground line VoutGnd of the power supply. One end of the output voltage sampling filter capacitor C11 is connected to the output power supply positive terminal Vout+ of the power supply, and the other end is connected to the output power supply ground line VoutGnd of the power supply.

[0036] The power MOS tube Q1 in the flyback power conversion circuit receives the output drive signal of the isolation drive circuit to realize switch control and duty cycle adjustment, and realizes magnetic isolation between the primary and secondary sides through the flyback transformer T1. Its basic working principle is: when the power MOS tube Q1 is turned on, the flyback transformer T1 stores energy, the output rectifier diode V1 is turned off, and the output filter capacitor C9 supplies power to the subsequent power load; when the power MOS tube Q1 is turned off, the flyback transformer T1 supplies power to the secondary side, the output rectifier diode V1 is turned on, the output filter capacitor C9 is charged, and the subsequent power load is supplied at the same time.

[0037] like Figure 4 As shown, the RCC auxiliary source power supply circuit adopts a high-frequency self-excited isolation RCC circuit, which is composed of a flyback transformer T2, an NPN transistor Q2, diodes V4-V8, a voltage regulator diode V9, capacitors C14-C17, a starting resistor R5 and a resistor R6.

[0038] Among them, one end of the starting resistor R5 is connected to the positive power supply line Vin2+ of the power circuit, that is, the 1st pin of the flyback transformer T2, and the other end is connected to the base of the transistor Q2. The collector of the transistor Q2 is connected to the 2nd pin of the flyback transformer T2, and the emitter of the transistor Q2 is connected to the power circuit power supply return line VinGnd2. The cathode of the diode V7 is connected to the base of the transistor Q2, and the anode is connected to the emitter of the transistor Q2. The cathode of the voltage-stabilizing diode V9 is connected to the base of the transistor Q2, and the anode is connected to the anode of the diode V5. One end of the resistor R6 is connected to the base of the transistor Q2, and the other end is connected to the cathode of the diode V6. The capacitor C15 is connected in parallel with the diode V6, and the anode of the diode V6 is connected to the cathode of the diode V5, that is, the 3rd pin of the flyback transformer T2. One end of the capacitor C16 is connected to the anode of the diode V5, and the other end is connected to the 4th pin of the flyback transformer T2, that is, the power circuit power supply return line VinGnd2. The anode of diode V4 is connected to pin 5 of flyback transformer T2, and the cathode is connected to the auxiliary source power supply positive terminal Vcc+. One end of capacitor C14 is connected to the auxiliary source power supply positive terminal Vcc+, and the other end is connected to pin 6 of flyback transformer T2, that is, the auxiliary source power supply return line CGnd. The anode of diode V8 is connected to pin 7 of flyback transformer T2, and the cathode is connected to the auxiliary source power supply return line CGnd. One end of capacitor C17 is connected to the auxiliary source power supply return line CGnd, and the other end is connected to pin 8 of flyback transformer T2, that is, the auxiliary source power supply negative terminal Vcc-. Pins 1, 3, 6 and 8 of flyback transformer T2 are the same-named terminals, and pins 2, 4, 5 and 7 are the same-named terminals.

[0039] The RCC auxiliary source power supply circuit realizes magnetic isolation and voltage stabilization output by self-excitation drive. The voltage stabilizing diode V9 controls the transistor Q2 to turn on by shunting the base of the transistor Q2; the capacitor C16 is a voltage storage capacitor. When the transistor Q2 is turned on, the voltage stabilizing diode V9 reversely breaks down. At this time, the voltage at the end of the capacitor C16 is approximately the reverse breakdown voltage of the voltage stabilizing diode V9; when the transistor Q2 is turned off, the voltage of the auxiliary winding Nb of the flyback transformer T2 is reversed, and the diode V5 is turned on to provide a charging circuit for the capacitor C16. The voltage of the auxiliary winding Nb is approximately the voltage at the end of the capacitor C16, that is, the reverse breakdown voltage of the voltage stabilizing diode V9. At this time, the output voltage of the RCC auxiliary source power supply circuit is proportional to the auxiliary winding voltage Nb. The RCC auxiliary source power supply circuit realizes output voltage stabilization control through the cooperation of the capacitor C16 and the voltage stabilizing diode V9. Since the voltage stabilization function of the circuit is realized by the breakdown of the voltage stabilizing diode, the use of high-precision voltage stabilizing diodes can improve the accuracy of its output voltage; the shunt control of the voltage stabilizing diode and the base current of the switching transistor realizes the feedback control function of the power output; the circuit can adapt to a wider input voltage range. The secondary side of the RCC auxiliary source power supply circuit adopts half-wave rectification to power the output voltage and current acquisition and control circuit and the PWM pulse width modulation circuit.

[0040] like Figure 5As shown, the output voltage and current acquisition and control circuit is composed of an output voltage acquisition circuit, an output voltage PID negative feedback control circuit, an output current acquisition circuit, an output current PID negative feedback control circuit and a feedback signal comparison circuit: Among them: The output voltage acquisition circuit is composed of differential adjustment resistors R7-R10, filter capacitors C18 and C19, operational amplifier N1, operational amplifier power supply current limiting protection resistors R11 and R12, power supply filter capacitors C20 and C21, and operational amplifier gain resistor R13. Among them, one end of the differential adjustment resistor R8 is connected to the positive end of the output voltage acquisition signal Vout+, and the other end is connected to the in-phase end of the operational amplifier N1; after the differential adjustment resistor R9 and the filter capacitor C18 are connected in parallel, one end is connected to the in-phase end of the operational amplifier N1, and the other end is connected to the auxiliary source power supply return line CGnd; one end of the differential adjustment resistor R7 is connected to the negative end of the output voltage acquisition signal VoutGnd, and the other end is connected to the inverting end of the operational amplifier N1; after the differential adjustment resistor R10 and the filter capacitor C19 are connected in parallel, one end is connected to the inverting end of the operational amplifier N1, and the other end is connected to the auxiliary source power supply return line CGnd. One end of the power supply current limiting protection resistor R11 is connected to the negative end of the auxiliary source power supply Vcc-, and the other end is connected to the negative power supply end of the operational amplifier N1. One end of the power supply filter capacitor C20 is connected to the negative power supply terminal of the operational amplifier N1, and the other end is connected to the auxiliary source power supply loop CGnd. One end of the power supply current limiting protection resistor R12 is connected to the auxiliary source power supply positive terminal Vcc+, and the other end is connected to the positive power supply terminal of the operational amplifier N1. One end of the power supply filter capacitor C21 is connected to the positive power supply terminal of the operational amplifier N1, and the other end is connected to the auxiliary source power supply loop CGnd. Both ends of the operational amplifier gain resistor R13 are connected to the gain setting terminal of the operational amplifier N1. The reference terminal of the operational amplifier N1 is connected to the auxiliary source power supply loop CGnd.

[0041] The output voltage acquisition circuit converts the power supply output voltage acquisition signal into the input signal of the subsequent output voltage PID negative feedback control circuit through the differential adjustment resistors R7-R10 and the operational amplifier gain resistor R13, and at the same time realizes high-resistance isolation between the power supply output power ground VoutGnd and the internal control ground CGnd, avoiding the ground disturbance on the load side of the power supply affecting the steady-state operation of the power supply during the operation of the power supply.

[0042] The output voltage PID negative feedback control circuit is composed of a dual operational amplifier N2 (op amp A part), resistors R21-R27 and capacitors C22-C27. Among them, resistor R21 is connected in series with capacitor C22 and then connected in parallel with resistor R22. One end of the resistor-capacitor network formed is connected to the output end of operational amplifier N1 in the output voltage acquisition circuit, and the other end is connected to the inverting end of operational amplifier N2A. Resistor R25 is connected in series with capacitor C25 and then connected in parallel with capacitor C24. One end of the resistor-capacitor network formed is connected to the inverting end of operational amplifier N2A, and the other end is connected to the output end of operational amplifier N2A. One end of resistor R23 is connected to the Vref end (reference voltage end) of the PWM controller in the PWM pulse width modulation circuit, and the other end is connected to the in-phase end of operational amplifier N2A. After resistor R24 ​​is connected in parallel with capacitor C23, one end is connected to the in-phase end of operational amplifier N2A, and the other end is connected to the auxiliary source power supply loop CGnd. One end of the power supply current limiting protection resistor R26 is connected to the auxiliary source power supply negative terminal Vcc-, and the other end is connected to the negative power supply terminal of the operational amplifier N2. One end of the power supply filter capacitor C26 is connected to the negative power supply terminal of the operational amplifier N2, and the other end is connected to the auxiliary source power supply return line CGnd. One end of the power supply current limiting protection resistor R27 is connected to the auxiliary source power supply positive terminal Vcc+, and the other end is connected to the positive power supply terminal of the operational amplifier N2. One end of the power supply filter capacitor C27 is connected to the positive power supply terminal of the operational amplifier N2, and the other end is connected to the auxiliary source power supply return line CGnd.

[0043] The output voltage PID negative feedback control circuit receives the voltage signal converted from the output voltage acquisition circuit, compares it with the threshold voltage of the op amp in-phase terminal, performs negative feedback PID loop operation, and finally forms an output voltage feedback signal. Resistors R23 and R24 are threshold voltage divider resistors, and the appropriate threshold voltage can be set by selecting different proportional resistance values.

[0044] The output current acquisition circuit is composed of differential adjustment resistors R14-R17, filter capacitors C33 and C35, operational amplifier N3, operational amplifier power supply current limiting protection resistors R18 and R19, power supply filter capacitors C32 and C34, and operational amplifier gain resistor R20. Among them, one end of the differential adjustment resistor R14 is connected to the positive end VoutGnd of the output current acquisition signal, and the other end is connected to the in-phase end of the operational amplifier N3; after the differential adjustment resistor R16 and the filter capacitor C35 are connected in parallel, one end is connected to the in-phase end of the operational amplifier N3, and the other end is connected to the auxiliary source power supply return line CGnd; one end of the differential adjustment resistor R15 is connected to the negative end Icj- of the output current acquisition signal, and the other end is connected to the inverting end of the operational amplifier N3; after the differential adjustment resistor R17 and the filter capacitor C33 are connected in parallel, one end is connected to the inverting end of the operational amplifier N3, and the other end is connected to the auxiliary source power supply return line CGnd. One end of the power supply current limiting protection resistor R19 is connected to the auxiliary source power supply negative terminal Vcc-, and the other end is connected to the negative power supply terminal of the operational amplifier N3. One end of the power supply filter capacitor C32 is connected to the negative power supply terminal of the operational amplifier N3, and the other end is connected to the auxiliary source power supply return line CGnd. One end of the power supply current limiting protection resistor R18 is connected to the auxiliary source power supply positive terminal Vcc+, and the other end is connected to the positive power supply terminal of the operational amplifier N3. One end of the power supply filter capacitor C34 is connected to the positive power supply terminal of the operational amplifier N3, and the other end is connected to the auxiliary source power supply return line CGnd. Both ends of the operational amplifier gain resistor R20 are connected to the gain setting end of the operational amplifier N3. The reference end of the operational amplifier N3 is connected to the auxiliary source power supply return line CGnd.

[0045] The output current acquisition circuit converts the power supply output current acquisition signal into the input signal of the subsequent output current PID negative feedback control circuit through the differential adjustment resistors R14-R17 and the operational amplifier gain resistor R20, and at the same time realizes high-resistance isolation between the power supply output power ground VoutGnd and the internal control ground CGnd, avoiding the ground disturbance on the load side of the power supply affecting the steady-state operation of the power supply during the operation of the power supply.

[0046] The output current PID negative feedback control circuit of the present invention is composed of a dual operational amplifier N2 (op amp B part), resistors R28-R32 and capacitors C28-C31. Among them, resistor R29 is connected in series with capacitor C30 and then connected in parallel with resistor R30, and one end of the resistor-capacitor network formed is connected to the output end of operational amplifier N3 in the output current acquisition circuit, and the other end is connected to the inverting end of operational amplifier N2B. Resistor R28 is connected in series with capacitor C29 and then connected in parallel with capacitor C28, and one end of the resistor-capacitor network formed is connected to the inverting end of operational amplifier N2B, and the other end is connected to the output end of operational amplifier N2B. One end of resistor R31 is connected to the Vref end of the PWM controller in the PWM pulse width modulation circuit, and the other end is connected to the in-phase end of operational amplifier N2B. After resistor R32 is connected in parallel with capacitor C31, one end is connected to the in-phase end of operational amplifier N2B, and the other end is connected to the auxiliary source power supply loop CGnd.

[0047] The output current PID negative feedback control circuit receives the converted voltage signal from the output current acquisition circuit, compares it with the threshold voltage of the op amp in-phase terminal, performs negative feedback PID loop operation, and finally forms an output current feedback signal. Resistors R31 and R32 are threshold voltage divider resistors, and the appropriate threshold voltage can be set by selecting different proportional resistance values.

[0048] The feedback signal comparison circuit is composed of resistors R33 and R34 and diodes V10-V13. One end of the resistor R33 is connected to the output end of the operational amplifier N2A, and the other end is connected to the cathodes of diodes V10 and V11. The anode of the diode V10 is connected to the auxiliary source power supply loop CGnd, and the anode of the diode V11 is connected to the COMP end of the PWM controller in the PWM pulse width modulation circuit. One end of the resistor R34 is connected to the output end of the operational amplifier N2B, and the other end is connected to the cathodes of diodes V12 and V13. The anode of the diode V13 is connected to the auxiliary source power supply loop CGnd, and the anode of the diode V12 is connected to the COMP end of the PWM controller in the PWM pulse width modulation circuit.

[0049] The feedback signal comparison circuit receives the output voltage feedback signal from the output voltage PID negative feedback control circuit and the output current feedback signal from the output current PID negative feedback control circuit, compares the two, takes the lower voltage value for output, and sends the final feedback signal to the COMP terminal of the PWM controller in the PWM pulse width modulation circuit to achieve closed-loop regulation. Diodes V10 and V13 are negative voltage clamping diodes to prevent the final feedback signal from being negative voltage, which affects the normal operation of the PWM pulse width modulation circuit.

[0050] The overall working mechanism of the output voltage and current acquisition and control circuit is: when the power supply output is high voltage and low current, the output voltage of the output current acquisition circuit is low, the output voltage of the output current PID negative feedback control circuit is higher than the output voltage of the output voltage PID negative feedback control circuit, and the power supply works in the voltage loop to achieve constant voltage and stable output. When the output current of the power supply increases to the set constant current output threshold, the output voltage of the output current PID negative feedback control circuit is lower than the output voltage of the output voltage PID negative feedback control circuit, and the power supply works in the current loop to achieve constant current and stable output. In this way, the power supply can perform adaptive adjustment of the constant voltage and constant current dual output mode according to the load impedance.

[0051] In addition, in the output voltage and current acquisition and control circuit of the present invention, as a preferred embodiment, an operational amplifier reverse follower circuit can be added at the subsequent stage of the output voltage acquisition circuit, and the output signal of the circuit is a telemetry signal of the power supply output voltage, thereby realizing the power supply output voltage telemetry function; an operational amplifier reverse follower circuit can be added at the subsequent stage of the output current acquisition circuit, and the output signal of the circuit is a telemetry signal of the power supply output current, thereby realizing the power supply output current telemetry function; the Vref level in the output voltage PID negative feedback control circuit can be replaced by an external injection level, thereby realizing the power supply output voltage remote control function; the Vref level in the output current PID negative feedback control circuit can be replaced by an external injection level, thereby realizing the power supply output current remote control function.

[0052] like Figure 6 As shown, the PWM pulse width modulation circuit is composed of a PNP transistor Q3, a diode V14, resistors R35-R41, capacitors C36-C41 and a PWM controller U1.

[0053] Among them, one end of the resistor R35 is connected to the cathode of the diode V14, and the other end is connected to the Vref end of the PWM controller U1; the anode of the diode V14 is connected to the base of the transistor Q3; one end of the resistor R37 is connected to the Vref end of the PWM controller U1, and the other end is connected to the anode of the diode V14; one end of the capacitor C36 is connected to the base of the transistor Q3, and the other end is connected to the collector of the transistor Q3, that is, the auxiliary source power supply loop CGnd; one end of the resistor R38 is connected to the Vref end of the PWM controller U1, and the other end is connected to the emitter of the transistor Q3, that is, the COMP end of the PWM controller U1; one end of the resistor R39 is connected to the FB end of the PWM controller U1 (the inverting input end of the internal error amplifier), and the other end is connected to the auxiliary source power supply loop CGnd; after the capacitor C37 and the resistor R40 are connected in parallel, one end is connected to the CS end of the PWM controller U1, and the other end is connected to the auxiliary source power supply loop CGnd; one end of the capacitor C38 is connected to the CS end of the PWM controller U1, and the other end is connected to the auxiliary source power supply loop CGnd. One end is connected to the RtCt end of the PWM controller U1 (the internal fixed frequency oscillator setting end); one end of the capacitor C39 is connected to the RtCt end of the PWM controller U1, and the other end is connected to the auxiliary source power supply return line CGnd; one end of the resistor R41 is connected to the RtCt end of the PWM controller U1, and the other end is connected to the Vref end of the PWM controller U1; one end of the capacitor C41 is connected to the Vref end of the PWM controller U1, and the other end is connected to the auxiliary source power supply return line CGnd; one end of the capacitor C40 is connected to the Vcc end (power supply end) of the PWM controller U1, and the other end is connected to the auxiliary source power supply return line CGnd; one end of the resistor R36 is connected to the auxiliary source power supply positive end Vcc+, and the other end is connected to the Vcc end of the PWM controller U1; the COMP end of the PWM controller U1 receives the feedback signal FFK from the output voltage and current acquisition and control circuit, and the OUT end (drive output end) of the PWM controller U1 transmits the PWM drive signal PWM-out to the subsequent isolation drive circuit.

[0054] PWM pulse width modulation circuit is based on single-ended drive controller ( Figure 6 The PWM controller U1 is UC1843. In actual working conditions, the single-ended drive controller can be selected but not limited to UC1843), which receives the primary current acquisition signal IS from the flyback power conversion circuit and the feedback signal FFK from the output voltage and current acquisition and control circuit, and realizes the functions of power supply slow start power-on, primary overcurrent protection, current slope compensation, PWM pulse width adjustment through its peripheral circuit, and sends its output PWM drive signal to the isolation drive circuit. By adjusting its peripheral circuit parameters, the power supply slow start power-on time and operating frequency can be adjusted, and the appropriate primary overcurrent protection threshold can be set.

[0055] like Figure 7As shown, the isolation driving circuit is composed of diodes V15-V18, resistors R42-R45, capacitors C42 and C43 and a driving transformer T3.

[0056] In the isolation drive circuit of the present invention, capacitor C42 is connected in parallel with diode V15, the cathode of diode V15 is connected to the OUT terminal of PWM controller U1 in PWM pulse width modulation circuit, and the anode of diode V15 is connected to one end of resistor R42; the other end of resistor R42 is connected to pin 1 of driving transformer T3; pin 2 of driving transformer T3 is connected to GND terminal (power ground terminal) of PWM controller U1 in PWM pulse width modulation circuit, i.e. auxiliary source power supply return line CGnd; capacitor C43 is connected in parallel with resistor R43, one end of which is connected to pin 3 of driving transformer T3, and the other end is connected to cathode of diode V16. ; The anode of diode V16 is connected to pin 4 of driving transformer T3, that is, output driving ground VinGnd2 (power circuit power supply return line VinGnd2); pins 1 and 3 of driving transformer T3 are the same-name terminals, and pins 2 and 4 are the same-name terminals; diode V17 is connected in parallel with resistor R44, the cathode of diode V17 is connected to the cathode of diode V16, and the anode of diode V17 is connected to the anode of diode V18; diode V18 is connected in parallel with resistor R45, and the cathode of diode V18 is the output Vgs+ terminal of the isolation driving circuit, which is connected to the gate of power MOS tube Q1 in the flyback power conversion circuit.

[0057] In the isolation drive circuit of the present invention, capacitor C42 is a primary side DC isolation capacitor to avoid the presence of a DC component in the primary current of the driving transformer, which causes the magnetic saturation of the transformer. Capacitor C43 and diode V16 can solve the problem that the amplitude of the circuit output driving voltage changes with the duty cycle when the circuit input side is driven by a single-end. Resistor R42, diode V15 and resistor R43 can solve the problem of residual driving of the circuit after the circuit input is powered off, and realize that capacitors C42 and C43 are quickly discharged and the driving transformer T3 is quickly magnetically reset after the circuit input is powered off. When the output is a high level, diode V18 is turned on, and resistor R44 is an output drive rising edge adjustment resistor; when the output is a low level, diode V17 is turned on, and resistor R45 is an output drive falling edge adjustment resistor. By adjusting the resistance values ​​of resistors R44 and R45, the rising edge and falling edge waveforms of the circuit output driving signal can be adjusted, thereby adjusting the opening and closing speed of the MOS tube, and solving the problems of oscillation and voltage spikes caused by distributed parameters in the power circuit.

[0058] In summary, the load impedance adaptive flyback power supply circuit and its implementation method of the present invention can improve the stability of the system, enhance the anti-interference ability of the system, realize load impedance adaptive output adjustment, and optimize power supply efficiency to a certain extent. In addition, the present invention can improve the accuracy and flexibility of control, and improve the convenience of maintenance by simplifying the circuit system.

[0059] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the specification and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A load impedance adaptive flyback power supply circuit, characterized in that: The circuit includes a filter circuit, a flyback power conversion circuit, an RCC auxiliary source power supply circuit, an output voltage and current acquisition and control circuit, a PWM pulse width modulation circuit and an isolation drive circuit; wherein: The input bus is filtered by the filtering circuit to supply power to the flyback power conversion circuit and the RCC auxiliary source power supply circuit; the flyback power conversion circuit provides voltage and current to the power load after completing the isolation conversion, and sends its output voltage and current acquisition signal to the output voltage and current acquisition and control circuit, and sends the primary current acquisition signal IS to the PWM pulse width modulation circuit; The RCC auxiliary source power supply circuit is used to: provide voltage and current to the output voltage and current acquisition and control circuit and the PWM pulse width modulation circuit through isolation conversion; The output voltage and current acquisition and control circuit is used to: form a voltage and current loop feedback signal FFK based on the power supply output voltage and current acquisition signal; The PWM pulse width modulation circuit is used to: perform power supply slow start, primary side overcurrent protection, current slope compensation and PWM pulse width adjustment based on the primary current acquisition signal IS and the voltage and current loop feedback signal FFK, and output a PWM drive signal to the isolation drive circuit; The isolation driving circuit is used to: output a MOS tube driving signal based on a PWM driving signal, realize primary and secondary ground line isolation, and control the on and off of the primary power MOS tube in the flyback power conversion circuit.

2. The load impedance adaptive flyback power supply circuit according to claim 1, characterized in that: The filter circuit comprises a common mode filter circuit and a differential mode filter circuit, and the common mode filter circuit and the differential mode filter circuit are used to eliminate the common mode and differential mode interference between the bus and the internal circuit of the power supply.

3. The load impedance adaptive flyback power supply circuit according to claim 1, characterized in that: The flyback power conversion circuit is a main power conversion circuit of a flyback power supply, and the flyback power conversion circuit is used to complete isolation conversion through a flyback DC-DC converter.

4. The load impedance adaptive flyback power supply circuit according to claim 3, characterized in that: The flyback power conversion circuit collects the primary current through the current transformer and sends the primary current collection signal IS to the PWM pulse width modulation circuit; receives the output drive signal from the isolation drive circuit to realize the switch control and duty cycle adjustment of the primary power MOS tube.

5. The load impedance adaptive flyback power supply circuit according to claim 1, characterized in that: The PWM pulse width modulation circuit includes a single-ended drive controller and its peripheral circuits, receives a primary current acquisition signal IS and a voltage-current loop feedback signal FFK, and outputs a PWM drive signal.

6. The load impedance adaptive flyback power supply circuit according to claim 1, characterized in that: The RCC auxiliary source power supply circuit includes a high-frequency self-excited magnetic isolation RCC circuit, and the RCC auxiliary source power supply circuit realizes magnetic isolation and voltage stabilization output by self-excited driving.

7. The load impedance adaptive flyback power supply circuit according to claim 1, characterized in that: The output voltage and current acquisition and control circuit comprises an output voltage acquisition circuit, an output voltage PID negative feedback control circuit, an output current acquisition circuit, an output current PID negative feedback control circuit and a feedback signal comparison circuit.

8. The load impedance adaptive flyback power supply circuit according to claim 7, characterized in that: The output voltage and current acquisition and control circuit performs differential amplification processing on the received power supply output voltage and current acquisition signal, and compares the processed signal with the threshold voltage of the PID negative feedback control circuit to form a voltage and current loop feedback signal FFK, which is sent to the PWM pulse width modulation circuit.

9. The load impedance adaptive flyback power supply circuit according to claim 1, characterized in that: The isolation drive circuit isolates and transforms the PWM drive signal into a MOS tube drive signal, and sends it to the primary power MOS tube in the flyback power conversion circuit to control the MOS tube switch; by adjusting the output side drive resistance in the isolation drive circuit, the rising edge and falling edge waveforms of the MOS tube drive signal are adjusted, thereby adjusting the on and off speed of the MOS tube.

10. The method for implementing the load impedance adaptive flyback power supply circuit according to any one of claims 1 to 9, characterized in that: The steps include: S1, filter the input bus to obtain a filtered input signal; perform power conversion on the filtered input signal to provide voltage and current for the power load, and collect the primary current collection signal IS; S2, RCC auxiliary source power supply circuit provides voltage and current for output voltage and current acquisition and control circuit and PWM pulse width modulation circuit; output voltage and current acquisition and control circuit performs differential amplification processing on output voltage and current acquisition signals, and forms voltage and current loop feedback signal FFK after loop operation; S3, PWM pulse width modulation circuit realizes power supply slow start, primary side overcurrent protection, current slope compensation and PWM pulse width adjustment based on primary current acquisition signal IS and voltage current loop feedback signal FFK, and generates PWM drive signal; S4. The isolation drive circuit outputs a MOS tube drive signal based on the PWM drive signal to achieve isolation of the primary and secondary ground lines, and controls the on and off of the primary power MOS tube in the flyback power conversion circuit, so that the flyback power supply can output voltage and current within the full load range.

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