Multi-voltage flyback converter

Abstract

The utility model relates to the technical field of power electronics and electricians, and discloses a multi-voltage flyback converter which at least comprises a transformer, an input circuit, a first output circuit, a first control circuit, a second output circuit and a control circuit used for the second output circuit. The transformer provides energy for the first output circuit through the first output winding and can also supplement energy for the second output circuit, and the control circuit of the first output circuit can realize that the first output circuit outputs energy and can also supplement energy for the second output circuit at the same time. The problem of low output voltage drift caused by insufficient energy in the second output circuit can be solved; the transformer provides energy for the second output circuit through the second output winding, and the control circuit of the second output circuit can effectively control energy transmission in the second output circuit, so that the problem of high voltage drift caused by excessive energy in the second output circuit can be solved.

Description

Technical Field

[0001] The utility model relates to the fields of power electronics technology and electrical engineering technology, and in particular to a multi-voltage flyback converter with a simple structure. Background Art

[0002] As various types of electrical equipment become increasingly complex, in electronic power supply systems, system power supplies often need to provide different power supplies for different loads, which further increases the demand for system power supply voltage levels and the number of channels, while also placing higher requirements on the quality and reliability of each output voltage.

[0003] A traditional method is to set up independent power supplies for different loads, but this power supply method has low integration and high system power supply cost. In order to improve the integration of the power supply system, ensure the quality of multi-channel output voltage, reduce system cost and increase reliability, the demand for multi-voltage power supplies is becoming increasingly prominent.

[0004] The current mainstream development of multi-voltage power supply systems mainly includes the following methods:

[0005] The first method is to realize multi-voltage power supply by setting multiple windings on the secondary side of the transformer, such as Figure 1 As shown. The first PWM controller detects the main output voltage V according to the feedback isolation unit. o1 To control the conduction state of the first rectifier switch Q1, a negative feedback loop is formed to perform closed-loop voltage regulation control on the main output voltage Vo1 signal, and the auxiliary output voltage V o2 By increasing the secondary winding N s2 This method is realized in an open-loop control mode. The advantage of this method is that the cost is low; the disadvantage is that the output voltage V o2 The current will be coupled with each other and affect each other. If the output load of a secondary winding changes greatly, it will also affect the output voltage V of other secondary windings. o2 Changes, that is, when the main output is fully loaded and the auxiliary output is lightly loaded, the auxiliary output voltage V o2 Will drift high; when the main output is lightly loaded and the auxiliary output is fully loaded, the auxiliary output voltage V o2 This method has a poor cross-regulation rate and is difficult to meet the application occasions where the auxiliary output voltage regulation accuracy requirements are high.

[0006] The second method is to use a low dropout linear regulator (LDO) at the output of the auxiliary circuit for linear regulation, such as Figure 2 As shown. Among them, the main output voltage V o1 The voltage regulation control is the same as the first method mentioned above, and will not be repeated here. The auxiliary output voltage V o2The voltage is regulated by a linear regulator (LDO). The advantage of this method is that the auxiliary voltage has a high accuracy; the disadvantage is that there is a certain voltage difference between the input and output of the linear regulator (LDO), which seriously affects the conversion efficiency of the auxiliary output. In particular, the larger the voltage difference, the more serious the power consumption of the linear regulator (LDO) when the auxiliary output is fully loaded, and the heat dissipation problem must be considered.

[0007] The third method: by adding a second-stage DC-DC conversion circuit at the output end of the auxiliary circuit, such as the commonly used Buck circuit or Boost circuit, the original output DC voltage is converted into another DC voltage, such as Figure 3 The advantage of this method is that the main and auxiliary outputs will not interfere with each other. Compared with the second method, the auxiliary conversion efficiency is greatly improved, which is more helpful to solve the heat dissipation problem. The disadvantage is that additional components such as switch tubes, inductors, and control chips are required, and the system cost is relatively high.

[0008] In this regard, Chinese patent document CN103178719B proposes a multi-voltage power supply solution to overcome the related defects. The circuit diagram is as follows: Figure 4 As shown. Among them, the main output voltage Vo1 is controlled by the first output voltage controller, and the auxiliary output voltage Vo2 is controlled by the second output voltage controller. The solution disclosed in the Chinese patent effectively solves the problem of the auxiliary output voltage drifting high under the extreme working conditions when the main output is fully loaded and the auxiliary output is lightly loaded. However, it still does not solve the problem of the auxiliary output voltage drifting low under the extreme working conditions when the main output is lightly loaded and the auxiliary output is fully loaded.

[0009] It should be noted that the above information disclosed in the background technology section is only intended to deepen the understanding of the overall background technology of the utility model, and should not be regarded as admitting or implying in any form that the information constitutes the prior art known to those skilled in the art. Utility Model Content

[0010] In view of this, the technical problem to be solved by the present invention is to provide a multi-voltage flyback converter in view of the defects and shortcomings of the prior art in the aforementioned background. It not only solves the problem of low output voltage of the auxiliary circuit under the extreme working condition when the main circuit output is lightly loaded and the auxiliary circuit output is fully loaded, but also can solve the problem of high output voltage of the auxiliary circuit under the extreme working condition when the main circuit output is fully loaded and the auxiliary circuit output is lightly loaded, thereby ensuring the requirements of high precision and low cross-regulation rate of the auxiliary circuit voltage within the full working condition range. At the same time, each output is independent of each other and does not affect each other, and each auxiliary circuit has an independent protection function. Once a short circuit, overload or other faults occur in one of the auxiliary circuits, only the faulty circuit is cut off from the system, and the normal operation of other circuits is not affected, and the reliability is high. In addition, the number of auxiliary output channels is also easy to expand.

[0011] In a multi-voltage power supply system, the cross-regulation rate is an important indicator to measure the power supply quality of each output voltage. Under the extreme working conditions of unbalanced loads, such as the main output with light load and the auxiliary output with full load, or the main output with full load and the auxiliary output with light load, the existing technology will cause the auxiliary output voltage to drift high or low, which will lead to a deterioration of the cross-regulation rate. The high drift of the auxiliary output voltage is caused by excessive auxiliary energy, and the low drift of the auxiliary output voltage is caused by insufficient auxiliary energy. Therefore, the overall concept of the utility model is: when the auxiliary output voltage drifts low due to insufficient auxiliary energy, the main circuit supplements energy for the auxiliary circuit through a control strategy, thereby ensuring the high accuracy of the auxiliary output voltage; when the auxiliary output voltage drifts high due to excessive auxiliary energy, the auxiliary energy transmission is prevented through a control strategy, thereby also ensuring the high accuracy of the auxiliary output voltage.

[0012] The utility model provides a multi-voltage flyback converter, which at least comprises: a transformer, an input circuit, a first output circuit and a second output circuit, wherein the transformer has a primary input winding, a secondary first output winding and a secondary second output winding; the input circuit has a first rectifier switch connected to the primary input winding; the first output circuit has a synchronous rectifier switch and a first output filter capacitor, wherein the first end of the synchronous rectifier switch is connected to the secondary first output winding, and the second end of the synchronous rectifier switch is connected to the first output filter capacitor; the second output circuit has a second rectifier switch and a second output filter capacitor, wherein the first end of the second rectifier switch is connected to the secondary second output winding, and the second end of the second rectifier switch is connected to the second output filter capacitor. The first output circuit also has a first control circuit, which has a PWM controller and an auxiliary circuit drive signal processing unit. The PWM controller is connected to the control end of the synchronous rectifier switch. The PWM controller determines the turn-on time of the synchronous rectifier switch by detecting the voltage of the first output winding on the secondary side, so that the first output winding on the secondary side provides energy for the first output circuit while also providing energy for the second output circuit. The auxiliary circuit drive signal processing unit is connected to the PWM controller. The auxiliary circuit drive signal processing unit identifies the working state of the second rectifier switch in the second output circuit, and outputs a turn-off control signal to the PWM controller when the second rectifier switch is turned off, so as to determine the turn-off time of the synchronous rectifier switch.

[0013] Preferably, the second output circuit also has a second control circuit, which is connected to the second rectifier switch, and is used to control the second rectifier switch to turn on during the conduction period of the first rectifier switch, and to control the second rectifier switch to turn off before the synchronous rectifier switch is turned off.

[0014] Preferably, the second control circuit has a first PWM controller, a signal processing module and a first reference error amplifier circuit. The signal processing module detects the voltage of the second output winding on the secondary side and enables the first PWM controller turn-on logic after a fixed delay to determine the turn-on time of the second rectifier switch. The first reference error amplifier circuit obtains a feedback voltage by detecting the output voltage of the second output circuit and compares the feedback voltage with the reference voltage in real time. When the feedback voltage reaches the reference voltage, the first reference error amplifier circuit outputs an enable signal to the first PWM controller to determine the turn-off time of the second rectifier switch.

[0015] Preferably, the moment when the PWM controller receives the shutdown control signal and detects that the voltage of the first output winding on the secondary side is greater than zero is determined as the shutdown moment of the synchronous rectification switch.

[0016] Preferably, the input circuit includes a second PWM controller, a feedback isolation unit and an absorption circuit. The second PWM controller controls the conduction state of the first rectifier switch according to the output voltage of the first output circuit detected by the feedback isolation unit, thereby realizing energy storage of the primary side input winding.

[0017] Preferably, the voltage of the second output winding on the secondary side is higher than the output voltage of the second output circuit.

[0018] Preferably, the first output winding on the secondary side and the second output winding on the secondary side are different windings, and the output voltage of the first output circuit and the output voltage of the second output circuit are both non-isolated outputs.

[0019] Preferably, the synchronous rectification switch is a metal oxide semiconductor field effect transistor or an insulated gate bipolar transistor;

[0020] Preferably, the second rectifying switch is a metal oxide semiconductor field effect transistor or an insulated gate bipolar transistor.

[0021] Preferably, the second output circuit is further provided with a rectifier diode, the anode of the rectifier diode is connected to the second output filter capacitor, and the cathode of the rectifier diode is connected to the second output winding on the secondary side.

[0022] Compared with the prior art, the multi-voltage flyback converter of the utility model has the following beneficial effects:

[0023] (1) The utility model sets a synchronous rectification switch in the first output circuit, so that the first output winding on the secondary side can transmit energy to the first output circuit and supplement energy to the second output circuit at the same time, so that under the extreme working conditions when the first output circuit is unloaded and the second output circuit is fully loaded, the output voltage of the second output circuit can maintain high accuracy, effectively improving the power supply quality;

[0024] (2) The utility model sets a second rectifier switch in the second output circuit, which effectively controls the energy transmission of the second output circuit, so that under the extreme working conditions when the first output circuit is fully loaded and the second output circuit is unloaded, the output voltage of the second output circuit can maintain high accuracy, effectively improving the power supply quality;

[0025] (3) The second output circuit of the utility model has an independent on-off control capability. When any one of the second output circuits is overloaded or even short-circuited, it can be disconnected from the system without affecting the normal operation of other output circuits, and the system reliability is high; BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of a commonly used multi-voltage power supply flyback converter circuit;

[0027] Figure 2 The schematic diagram of the existing multi-voltage power supply flyback converter circuit using LDO for voltage stabilization;

[0028] Figure 3 The schematic diagram of the circuit of a multi-voltage power supply flyback converter using a two-stage power conversion circuit is provided;

[0029] Figure 4 It is a circuit schematic diagram of an embodiment in Chinese patent document CN103178719B;

[0030] Figure 5 This is a circuit schematic diagram of a multi-voltage flyback converter of the utility model;

[0031] Figure 6 According to the utility model Figure 5 A circuit diagram of a first control circuit in a first output circuit in;

[0032] Figure 7 According to the utility model Figure 5 A circuit diagram of a second control circuit of a second output circuit in;

[0033] Figure 8 This is a working timing diagram of the multi-voltage flyback converter of the utility model. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the utility model more clear, the technical solution of the utility model will be described more clearly and completely in combination with the accompanying drawings and specific embodiments.

[0035] See also Figure 5, is a circuit schematic diagram of the multi-voltage flyback converter of the utility model. According to the operating environment and application requirements, the multi-voltage flyback converter can be configured to output N (N is a natural number greater than or equal to 2) output voltages. If the number of output channels is N, the transformer includes N secondary-side output windings, and the secondary-side output circuit can be connected to each of the N secondary-side output windings. The following is an example of a multi-voltage flyback converter with two output circuits on the secondary side.

[0036] like Figure 5 As shown, the multi-voltage flyback converter includes: a transformer T, an input circuit, a first output circuit 51 and a second output circuit 52. The input power supply V in The energy is converted and transmitted to the first output circuit 51 and the second output circuit 52 through the transformer T via the input circuit. The transformer T has at least a primary input winding T p , the first output winding T on the secondary side s1 And the secondary side second output winding T s2 The first output circuit 51 is used as the main output circuit (hereinafter referred to as the main circuit), and the second output circuit 52 is used as the auxiliary output circuit (hereinafter referred to as the auxiliary circuit). p Connect to the input power supply V in , input power supply V in After input filter capacitor C in And through the input circuit to the primary side input winding T p The first output circuit 51 is connected to the first output winding T on the secondary side. s1 , and generate the main output voltage V o1 (The output voltage of the first output circuit V o1 ).

[0037] The first output circuit 51 at least includes: a synchronous rectification switch SR, a first output filter capacitor C o1 and a first control circuit, a first end of the synchronous rectification switch SR and a first output winding T on the secondary side s1 The second end of the synchronous rectifier switch SR is connected to the first output filter capacitor C o1 Connection, secondary side first output winding T s1 The current passes through the synchronous rectification switch SR and the first output filter capacitor C o1 The rectifier filter circuit rectifies the output and generates the main output voltage V o1 And give the first load R o1 In this embodiment, the synchronous rectification switch SR is a MOSFET tube. The second output circuit 52 is connected to the second output winding T s2 , and generate auxiliary output voltage V o2 (The output voltage of the second output circuit Vo2 ).

[0038] The second output circuit 52 at least includes: a rectifier diode D o , the second rectifier switch Q2, the second output filter capacitor C o2 and a second control circuit, wherein a first end of a second rectifier switch Q2 is connected to a second output winding T on a secondary side. s2 The second end of the second rectifier switch Q2 is connected to the second output filter capacitor C o2 Connection, rectifier diode D o The anode of the second output filter capacitor C o2 Connection, rectifier diode D o The cathode of the secondary side is connected to the second output winding T s2 The second output winding T s2 The current passes through the rectifier diode D o , the second rectifier switch Q2 and the second output filter capacitor C o2 The rectifier filter circuit rectifies the output and generates an auxiliary output voltage V o2 And give the second load R o2 powered by.

[0039] In this embodiment, the first output winding on the secondary side and the second output winding on the secondary side are different windings, and the main output voltage V o1 With the auxiliary output voltage V o2 All are non-isolated outputs. The voltage of the second output winding on the secondary side is higher than the auxiliary output voltage V o2 output voltage.

[0040] The input circuit at least includes: a first rectifier switch Q1, a second PWM controller, a feedback isolation unit and an absorption circuit. in After input filter capacitor C in Connect to the primary input winding T p A series circuit with the first rectifier switch Q1 is used to input the winding T to the primary side. p The second PWM controller detects the main output voltage V according to the feedback isolation unit. o1 To control the conduction state of the first rectifier switch Q1, thereby adjusting the input power supply V in Energy is stored in the transformer T to form voltage negative feedback control. In this embodiment, the first rectifier switch Q1 can be a MOSFET tube or other controllable switch elements. In addition, the absorption circuit is mainly used to reduce the influence of parasitic parameters to ensure that the first rectifier switch Q1 works reliably. Figure 5 Auxiliary circuit parts such as auxiliary power supply, current sampling and switch drive circuit have been omitted.

[0041] Specifically, if the first rectifier switch Q1 is in the on state (the switch is closed), the first output winding T s1 With the second output winding T s2 The polarity induced in the transformer T is the same as the primary input winding T p The voltages with opposite polarities cause the synchronous rectification switch SR and the rectification diode D included in the first output circuit 51 and the second output circuit 52 to be disconnected. o Therefore, the output current flowing through the first output circuit 51 and the second output circuit 52 is blocked, and only the first output filter capacitor C o1 The first load R o1 Provide energy, the second output filter capacitor C o2 The second load R o2 Provide energy. Input power V in The transmitted energy is stored in the form of magnetic induction of the transformer T. If the first rectifier switch Q1 on the primary side is in the off state (the switch is open), the first output winding T on the secondary side s1 With the second output winding T s2 The polarity induced in the transformer T is the same as the primary input winding T p The voltages with opposite polarities cause the synchronous rectification switch SR and the rectification diode D included in the first output circuit 51 and the second output circuit 52 to be disconnected. o Therefore, the induced current generated by the change of the magnetic induction of the transformer T is synchronously transmitted to the first output circuit 51 and the second output circuit 52.

[0042] The utility model particularly improves the first output circuit 51. The first control circuit in the first output circuit 51 includes: a PWM controller 511 and an auxiliary circuit drive signal processing unit 512. The PWM controller 511 is used to control the on and off operation of the synchronous rectification switch SR to ensure that the first output winding T s1 In addition to transmitting energy to the first output circuit 51, it can also transmit energy to the second output winding T s2 At the same time, energy is provided to the second output circuit 52, so that the auxiliary output voltage can maintain high accuracy under the extreme working conditions when the main output is unloaded and the auxiliary output is fully loaded.

[0043] In a specific embodiment, Figure 6 As shown, the PWM controller 511 includes a comparator U1, a comparator U2, a trigger U3 and an AND gate U4. The inverting input terminal of the comparator U1 is connected to the first output winding T s1The non-inverting input terminal of the comparator U1 is connected to the reference voltage Vth set inside the PWM controller 511, the output terminal of the comparator U1 is connected to the set S terminal of the trigger U3, and the non-inverting input terminal of the comparator U2 is connected to the first output winding T of the secondary side. s1 The inverting input terminal of the comparator U2 is connected to the ground (the voltage is zero), the output terminal of the comparator U2 is connected to the first input terminal of the AND gate U4, the second input terminal of the AND gate U4 is connected to the signal slope identification unit 512, the output terminal of the AND gate U4 is connected to the reset R terminal of the trigger U3, and the output terminal of the trigger U3 is connected to the control terminal of the synchronous rectification switch SR.

[0044] Figure 8 The working timing diagram of the multi-voltage flyback converter of the utility model is shown in FIG. gQ1 is the driving signal of the first rectifier switch Q1, V gQ2 is the driving signal of the second rectifier switch Q2, V gSR is the driving signal of the synchronous rectification switch SR, i p The primary input winding T p The current, i s1 The first output winding T on the secondary side s1 The current, i s2 The second output winding T s2 The current. Figure 5 As shown in FIG. 1 , the PWM controller 511 detects the first output winding T on the secondary side. s1 The voltage of the synchronous rectifier switch SR is used to determine the turn-on time of the synchronous rectifier switch SR, and the turn-off time of the synchronous rectifier switch SR is determined according to the enable signal sent by the auxiliary circuit drive signal processing unit 512, so as to further determine the drive duty cycle of the synchronous rectifier switch SR. Figure 6 As shown in FIG, after the first rectifier switch Q1 on the primary side of the transformer T is turned off, when the first output winding T on the secondary side s1 When the voltage is less than the reference voltage Vth set inside the PWM controller 511, the logic signal CS_ON output by the comparator U1 enables the PWM controller 511 to control the synchronous rectification switch SR to turn on. s1 While transmitting energy to the first output circuit 51, it also replenishes energy for the second output circuit 52. Figure 8 As shown in the energy replenishment area. When the driving signal V gQ2 When the secondary side first output winding T is turned off (that is, when the second rectifier switch is turned off), the auxiliary circuit driving signal processing unit 512 will send a shutdown control signal to the PWM controller. When the PWM controller receives the shutdown control signal, if it detects that the secondary side first output winding T s1When the voltage is greater than the reference voltage zero inside the PWM controller 511, the AND gate U4 outputs a logic signal CS_OFF to enable the PWM controller 511 to control the synchronous rectification switch SR to turn off. s1 The current in the first synchronous rectification switch SR and the first output filter capacitor C o1 Rectification and filtering form the main output voltage V o1 , is the first load R o1 Provide high-quality power supply.

[0045] refer to Figure 5 , Figure 7 , the second control circuit in the second output circuit includes: a signal processing module 521, a first PWM controller 522 and a first reference error amplifier circuit 523. The first PWM controller 522 is used to control the on and off operation of the second rectifier switch Q2, thereby effectively controlling the energy transmitted to the second output circuit 52 by the transformer T, so as to achieve the auxiliary output voltage to maintain high accuracy under the extreme working conditions when the main output is fully loaded and the auxiliary output is unloaded.

[0046] Among them, the first PWM controller 522 determines the turn-on time of the second rectifier switch Q2 through the enable signal of the signal processing module 521, and determines the turn-off time of the second rectifier switch Q2 according to the enable signal of the first reference error amplifier circuit 523, so as to further determine the driving duty cycle of the second rectifier switch Q2.

[0047] In a specific embodiment, the signal processing module 521 includes a slope detection unit, a fixed delay unit and a predetermined slope generation unit; the first PWM controller 522 includes a trigger U5 and a comparator U6; the first reference error amplifier circuit 523 includes a comparator U7, a capacitor C1, a resistor R1, a resistor R2 and a resistor R3. s1 The output of the slope detection unit is connected to the input of the fixed delay unit, and the output of the fixed delay unit is connected to the set S terminal of the trigger U5; the input of the predetermined slope generating unit is connected to the first output winding T of the secondary side. s1 The output of the predetermined slope generating unit is connected to the in-phase terminal of the comparator U6; the resistor R1 and the resistor R2 are connected in series, one end of which is grounded, and the other end is connected to the output voltage V of the second output circuit 52 o2 , capacitor C1 and resistor R3 are connected in series, one end of which is connected to the output of comparator U7 and the inverting input of comparator U6, and the other end is connected to the inverting input of comparator U7 and the middle end of resistor R1 and resistor R2. The in-phase input of comparator U7 is connected to the internally set reference voltage V refThe output terminal of the comparator U6 is connected to the reset R terminal of the trigger U5, and the output terminal of the trigger U5 is connected to the control terminal of the second rectifier switch Q2.

[0048] The working principle of the second control circuit is as follows:

[0049] When the first rectifier switch Q1 on the primary side of the transformer T is turned on, the second output winding T s2 The voltage is reversed, and the signal processing module 521 detects the voltage signal using the slope detection unit, and after a delay of a time period Td by the fixed delay unit, the first PWM controller 522 is enabled to control the second rectifier switch Q2 to turn on. s2 The voltage has not yet reversed, and the drain voltage of the second rectifier switch Q2 is less than the source voltage, so that the MOS body diode performs voltage clamping, which can make the second rectifier switch Q2 achieve zero voltage turn-on effect, so that the turn-on loss is greatly reduced. When the first rectifier switch Q1 on the primary side of the transformer T is turned off, the second output winding T on the secondary side s2 The voltage is reversed, and the reversed secondary side second output winding T s2 The voltage signal enables the predetermined slope generating unit to generate a slope signal. When the slope voltage reaches the output voltage signal of the first reference error amplifier circuit 523, the first PWM controller 522 is enabled to control the second rectifier switch Q2 to turn off. Figure 8 As shown in , the time between ta and tc is the on-time of the first rectifier switch Q1 , and the second rectifier switch Q2 only needs to be turned on during this time.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions and implementation methods of the utility model and should not be regarded as limiting the utility model. Although the utility model is described in detail with reference to the above embodiments, ordinary technicians in this field should understand that they can still make some improvements and modifications to the technical solutions recorded in the above embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements should also be regarded as the protection scope of the technical solutions of the embodiments of the utility model.

Claims

1. A multi-voltage flyback converter, characterized in that: At least: A transformer having a primary side input winding, a secondary side first output winding, and a secondary side second output winding; An input circuit having a first rectifier switch connected to the primary-side input winding; a first output circuit, comprising a synchronous rectification switch and a first output filter capacitor, wherein a first end of the synchronous rectification switch is connected to the first output winding on the secondary side, and a second end of the synchronous rectification switch is connected to the first output filter capacitor; a second output circuit, comprising a second rectifier switch and a second output filter capacitor, wherein a first end of the second rectifier switch is connected to the second output winding on the secondary side, and a second end of the second rectifier switch is connected to the second output filter capacitor; The first output circuit also has a first control circuit, which has a PWM controller and an auxiliary drive signal processing unit. The PWM controller is connected to the control end of the synchronous rectification switch. The PWM controller determines the turn-on time of the synchronous rectification switch by detecting the voltage of the first output winding on the secondary side, so that the first output winding on the secondary side provides energy to the first output circuit while also providing energy to the second output circuit. The auxiliary drive signal processing unit is connected to the PWM controller. The auxiliary drive signal processing unit identifies the working state of the second rectification switch in the second output circuit, and outputs a turn-off control signal to the PWM controller when the second rectification switch is turned off, so as to determine the turn-off time of the synchronous rectification switch.

2. The multi-voltage flyback converter according to claim 1, characterized in that: The second output circuit also has a second control circuit, which is connected to the second rectifier switch. The second output circuit is used to control the second rectifier switch to turn on during the conduction period of the first rectifier switch, and to control the second rectifier switch to turn off before the synchronous rectifier switch is turned off.

3. The multi-voltage flyback converter according to claim 2, characterized in that: The second control circuit comprises a first PWM controller, a signal processing module and a first reference error amplifier circuit. The signal processing module detects the voltage of the second output winding on the secondary side and enables the first PWM controller turn-on logic after a fixed delay to determine the turn-on time of the second rectifier switch. The first reference error amplifier circuit detects the feedback voltage obtained by the output voltage of the second output circuit and compares the feedback voltage with the reference voltage in real time. When the feedback voltage reaches the reference voltage, the first reference error amplifier circuit outputs an enable signal to the first PWM controller to determine the turn-off time of the second rectifier switch.

4. The multi-voltage flyback converter according to claim 1, characterized in that: The moment when the PWM controller receives the shutdown control signal and detects that the voltage of the first output winding on the secondary side is greater than zero is determined as the shutdown moment of the synchronous rectification switch.

5. The multi-voltage flyback converter according to claim 1, characterized in that: The input circuit includes a second PWM controller, a feedback isolation unit and an absorption circuit. The second PWM controller controls the conduction state of the first rectifier switch according to the output voltage of the first output circuit detected by the feedback isolation unit, thereby realizing energy storage of the primary side input winding.

6. The multi-voltage flyback converter according to claim 1, characterized in that: The voltage of the second output winding on the secondary side is higher than the output voltage of the second output circuit.

7. The multi-voltage flyback converter according to claim 1, characterized in that: The first output winding on the secondary side and the second output winding on the secondary side are different windings, and the output voltage of the first output circuit and the output voltage of the second output circuit are both non-isolated outputs.

8. The multi-voltage flyback converter according to claim 1, characterized in that: The synchronous rectification switch is a metal oxide semiconductor field effect transistor or an insulated gate bipolar transistor.

9. The multi-voltage flyback converter according to claim 1, characterized in that: The second rectifying switch is a metal oxide semiconductor field effect transistor or an insulated gate bipolar transistor.

10. The multi-voltage flyback converter according to claim 1, characterized in that: The second output circuit is further provided with a rectifier diode, the anode of the rectifier diode is connected to the second output filter capacitor, and the cathode of the rectifier diode is connected to the second output winding on the secondary side.

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