CN113037098A

CN113037098A - Flyback switching power supply conversion circuit

Info

Publication number: CN113037098A
Application number: CN202110484247.5A
Authority: CN
Inventors: 王卫江; 汪本强; 王贵旭; 旷文敏; 张信家
Original assignee: Shenzhen Huntkey Electric Co Ltd
Current assignee: Shenzhen Huntkey Electric Co Ltd
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2021-06-25

Abstract

The invention discloses a flyback switching power supply conversion circuit which comprises a forward auxiliary winding rectifying circuit, wherein when the output end of an output rectifying filter circuit is in short circuit, the voltage of the output end of the forward auxiliary winding rectifying circuit is not zero, and power can be supplied to a feedback control circuit, so that the feedback control circuit can work all the time, an extra transformer and other devices with larger volume and higher cost are not needed, the cost and the volume of a switching power supply are reduced, and the application scenes of the switching power supply are increased.

Description

Flyback switching power supply conversion circuit

Technical Field

The invention relates to the field of power conversion, in particular to a flyback switching power conversion circuit.

Background

Referring to fig. 1, fig. 1 is a block diagram of a switching power supply conversion circuit in the prior art, wherein the switching power supply conversion circuit includes a high-frequency switching circuit 10, a transformer 20, an output rectifying and filtering circuit 30, a switching control circuit 40, and a feedback control circuit 50, wherein the feedback control circuit 50 feeds back an output current and a voltage of the switching power supply to the switching control circuit 40, so that the switching control circuit 40 controls the high-frequency switching circuit 10 according to the output current and the voltage to realize closed-loop control of the output current of the switching power supply, and the feedback control circuit 50 is powered by a power supply output by the output rectifying and filtering circuit 30.

In this case, when the output load terminal of the switching power supply is short-circuited, there are two short-circuit protection methods in the prior art, in which the switch control circuit 40 controls the high-frequency switching circuit 10 to intermittently output the power supply so that the output current of the switching power supply is in an intermittent hiccup state. Specifically, when the output load terminal of the switching power supply is short-circuited, the output current of the switching power supply is large, the feedback control circuit 50 compares a large output current signal with a set value, and after the compared control signal is fed back to the switching control circuit 40 through the optical coupler, the switching control circuit 40 makes the switching power supply intermittently output current, which is specifically represented as: after the switch control circuit 40 receives the control feedback signal, the switch power supply temporarily stops outputting current, after a period of time, the switch power supply is controlled to output current, the feedback control circuit 50 compares the output current with a set value and feeds the result back to the switch control circuit 40, and if the output current is reduced to the set value, the switch power supply is controlled to output normal current; and if the output current is still larger than the set value, controlling the switching power supply to continuously keep the state of intermittent output current. Secondly, when the switching power supply supplies power to a plurality of subsystems simultaneously, if a short-circuit fault occurs in a certain subsystem, at this time, the first short-circuit protection mode exists that all subsystems in the system are in an intermittent power-on and power-off state, so that the fault plane of the system is enlarged, and the damage of the subsystem without the short-circuit fault may be caused, at this time, the high-frequency switching circuit 10 is generally controlled by the feedback control circuit 50 and the switching control circuit 40 to enable the switching power supply to continuously output a fixed current, and then the input fuse in the subsystem with the short-circuit fault is blown, so that the subsystem is separated from the switching power supply, and thus other subsystems can keep working normally, and the enlargement of the fault plane of the system and the damage of the subsystem without the short-circuit fault are avoided.

At present, a flyback switching power supply is generally used as a switching power supply with smaller power, and specifically, a current input end of a primary winding of a transformer and a current output end of a secondary winding in the flyback switching power supply are different terminals. At this time, for the second short-circuit protection method, if the output load end of the switching power supply is short-circuited, the voltage between the output positive end and the output negative end of the output rectifying and filtering circuit 30 is zero, and cannot supply power to the feedback control circuit 50, and the feedback control circuit cannot continuously feed back the feedback control signal to the switching control circuit, so that the switching control circuit 40 cannot control the high-frequency switching circuit 10 to make the switching power supply continuously output a fixed current, which may cause that the subsystem with the short-circuit fault cannot be separated from the switching power supply, may cause all subsystems in the system to be in an intermittent power-on and power-off state, and may also cause the switching power supply and other subsystems to be damaged.

In order to solve the above technical problem, an auxiliary power conversion circuit is provided in the prior art, which supplies power to the feedback control circuit 50 when a short circuit occurs between the output positive terminal and the output negative terminal of the switching power supply. Referring to fig. 2, fig. 2 is a block diagram of a conversion circuit with an auxiliary power supply in the prior art, the conversion circuit with an auxiliary power supply includes an auxiliary high frequency switch circuit 80, an auxiliary transformer 90, an auxiliary output rectifying and filtering circuit 100, an auxiliary switch control circuit 110, and an auxiliary feedback control circuit 120, in which the auxiliary feedback control circuit 120 feeds back an output voltage signal of the auxiliary power supply switch conversion circuit to the auxiliary switch control circuit 110, so that the auxiliary switch control circuit 110 controls the auxiliary high frequency switch circuit 80 according to the feedback signal to make the auxiliary power supply conversion circuit output a voltage capable of supplying power to the feedback control circuit 120. However, in this method, the auxiliary transformer 90 is required, and the added auxiliary transformer 90 has a large volume and high cost, which limits the application scenarios of the switching power supply.

Disclosure of Invention

The invention aims to provide a flyback switching power supply conversion circuit which can supply power to a feedback control circuit, so that the feedback control circuit can work all the time, an extra transformer is not needed, the size of the transformer is larger, devices with higher cost are not needed, the cost and the size of the switching power supply are reduced, and application scenes of the switching power supply are increased.

In order to solve the technical problems, the invention provides a flyback switching power supply conversion circuit which comprises a high-frequency switching circuit, a transformer, an output rectifying filter circuit, a switching control circuit and a feedback control circuit, wherein the output end of the output rectifying filter circuit is connected with the input end and the power end of the feedback control circuit; the device also comprises a forward auxiliary winding rectifying circuit;

the forward auxiliary winding rectifier circuit comprises: the output end of the forward auxiliary winding rectifying circuit is connected with the power supply end of the feedback control circuit and used for supplying power to the feedback control circuit when the output end of the output rectifying and filtering circuit is short-circuited.

Preferably, when the output voltage of the output rectifying and filtering circuit is not within the voltage range required by the power supply end of the feedback control circuit, the conversion circuit further comprises a flyback auxiliary winding rectifying circuit;

the flyback auxiliary winding rectifying circuit comprises: the output end of the flyback auxiliary winding rectifying circuit is connected with the power supply end of the feedback control circuit and used for supplying power to the feedback control circuit when the output end of the output rectifying and filtering circuit is not short-circuited.

Preferably, the conversion circuit further comprises a fourth diode;

and the anode of the fourth diode is connected with the output end of the output rectifying and filtering circuit, and the cathode of the fourth diode is connected with the power supply end of the feedback control circuit.

Preferably, the conversion circuit further comprises a voltage stabilizing circuit;

the forward auxiliary winding rectifying circuit is connected with the output end of the flyback auxiliary winding rectifying circuit to serve as a first node, the input end of the voltage stabilizing circuit is connected with the first node, and the output end of the voltage stabilizing circuit is connected with the power supply end of the feedback control circuit and used for stabilizing the voltage of the first node at a fixed value so as to supply power for the feedback control circuit.

Preferably, the voltage stabilizing circuit comprises a sixth resistor, a controllable switch, a voltage stabilizing diode and a fifth capacitor;

the first end of the sixth resistor is connected to the first end of the controllable switch and the first node, the second end of the sixth resistor is connected to the cathode of the zener diode and the control end of the controllable switch, the anode of the zener diode is connected to the first end of the fifth capacitor and the ground, and the second end of the fifth capacitor is connected to the second end of the controllable switch and the power end of the feedback control circuit.

Preferably, the forward auxiliary winding rectifying circuit comprises a fifth secondary winding, a second diode, a third diode and a first inductor;

the synonym end of the fifth primary winding is connected with the cathode of the second diode, the homonym end of the fifth primary winding is respectively connected with the cathode of the third diode and the first end of the first inductor, the anode of the second diode is respectively connected with the anode of the third diode and the ground, and the second end of the first inductor is connected with the first node;

the turn ratio of the first primary winding to the fifth secondary winding and the inductance of the first inductor are related to the output voltage of the forward auxiliary winding rectifying circuit.

the dotted terminal of the fifth primary winding is connected to the anode of the second diode, the dotted terminal of the fifth primary winding is connected to the anode of the third diode and the ground, the cathode of the second diode is connected to the cathode of the third diode and the first end of the first inductor, and the second end of the first inductor is connected to the first node;

Preferably, the flyback auxiliary winding rectifying circuit comprises a fourth secondary winding, a first diode and a first capacitor;

the homonymous end of the fourth secondary winding is connected with the cathode of the first diode, the synonym end of the fourth secondary winding is respectively connected with the first end of the first capacitor and the first node, and the other end of the first capacitor is respectively connected with the anode of the fifth diode and the ground;

the turn ratio of the first primary winding to the fourth secondary winding is related to the output voltage of the flyback auxiliary winding rectifying circuit.

the second end of the first capacitor is connected with the same-name end of the fourth secondary winding and the ground;

Preferably, the secondary auxiliary power supply module comprises the forward auxiliary winding rectifying circuit, the flyback auxiliary winding rectifying circuit and the voltage stabilizing circuit, and the conversion circuit further comprises a primary auxiliary power supply module;

the primary auxiliary power supply module comprises a primary forward auxiliary winding rectifying circuit, a primary flyback auxiliary winding rectifying circuit and a primary voltage stabilizing circuit;

the primary forward auxiliary winding rectifying circuit and the forward auxiliary winding rectifying circuit have the same structure; the primary flyback auxiliary winding rectifying circuit has the same structure as the flyback auxiliary winding rectifying circuit, and the primary voltage stabilizing circuit has the same circuit structure as the voltage stabilizing circuit;

the output end of the primary voltage stabilizing circuit is connected with the power supply end of the switch control circuit and used for supplying power to the switch control circuit.

The invention provides a flyback switching power supply conversion circuit which comprises a forward auxiliary winding rectifying circuit, wherein when the output end of an output rectifying filter circuit is in short circuit, the voltage of the output end of the forward auxiliary winding rectifying circuit is not zero, and power can be supplied to a feedback control circuit, so that the feedback control circuit can work all the time, an extra transformer and other devices with larger volume and higher cost are not needed, the cost and the volume of a switching power supply are reduced, and the application scenes of the switching power supply are increased.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed in the prior art and the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Fig. 1 is a block diagram of a switching power supply conversion circuit in the prior art;

FIG. 2 is a block diagram of a switching circuit with an auxiliary power supply according to the prior art;

FIG. 3 is a waveform diagram illustrating voltages at the first primary winding and the fourth secondary winding of the transformer during hiccup protection in the prior art;

FIG. 4 is a waveform diagram of an output voltage of the output rectifying and filtering circuit;

fig. 5 is a block diagram of a flyback switching power supply conversion circuit according to a first embodiment of the present invention;

fig. 6 is a block diagram of a flyback switching power supply conversion circuit according to a second embodiment of the present invention;

fig. 7 is a schematic waveform diagram of output voltages of the first primary winding, the fourth secondary winding and the fifth secondary winding when there is no short circuit at the output end of the output rectifying and filtering circuit provided by the present invention;

fig. 8 is a schematic waveform diagram of output voltages of the output rectifying filter circuit, the flyback auxiliary winding rectifying circuit and the forward auxiliary winding rectifying circuit when there is no short circuit at the output end of the output rectifying filter circuit provided by the present invention;

fig. 9 is a schematic waveform diagram of output voltages of the first primary winding, the fourth secondary winding and the fifth secondary winding when the output end of the output rectifying and filtering circuit provided by the invention is short-circuited;

fig. 10 is a schematic waveform diagram of output voltages of the output rectifying filter circuit, the flyback auxiliary winding rectifying circuit, and the forward auxiliary winding rectifying circuit when the output terminal of the output rectifying filter circuit is short-circuited;

FIG. 11 is a circuit diagram of a voltage regulator circuit according to the present invention;

FIG. 12 is a schematic circuit diagram of a first forward auxiliary winding rectifier circuit provided in the present invention;

FIG. 13 is a schematic circuit diagram of a second forward auxiliary winding rectifier circuit provided in the present invention;

FIG. 14 is a schematic circuit diagram of a third forward auxiliary winding rectifier circuit provided in the present invention;

FIG. 15 is a schematic circuit diagram of a fourth forward auxiliary winding rectifier circuit according to the present invention;

FIG. 16 is a schematic circuit diagram of a fifth forward auxiliary winding rectifier circuit provided in the present invention;

fig. 17 is a schematic circuit diagram of a sixth forward auxiliary winding rectifier circuit provided in the present invention;

fig. 18 is a schematic circuit diagram of a flyback auxiliary winding rectifier circuit according to the first embodiment of the present invention;

fig. 19 is a schematic circuit diagram of a flyback auxiliary winding rectifier circuit according to a second embodiment of the present invention;

fig. 20 is a schematic circuit diagram of a third flyback auxiliary winding rectifier circuit provided in the present invention;

fig. 21 is a schematic circuit diagram of a fourth flyback auxiliary winding rectifier circuit provided in the present invention;

fig. 22 is a schematic circuit diagram of a fifth flyback auxiliary winding rectifier circuit provided in the present invention;

fig. 23 is a schematic circuit diagram of a sixth flyback auxiliary winding rectifier circuit according to the present invention.

Detailed Description

The core of the invention is to provide a flyback switching power supply conversion circuit which can supply power to a feedback control circuit, so that the feedback control circuit can work all the time, and extra transformers which are large in size and high in cost are not needed, the cost and the size of the switching power supply are reduced, and the application scenes of the switching power supply are increased.

In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 3 and 4, fig. 3 is a schematic diagram of waveforms of voltages at a first primary winding and a fourth secondary winding of a transformer during hiccup protection in the prior art, and fig. 4 is a schematic diagram of a waveform of an output voltage of an output rectifying and filtering circuit.

Wherein v is the oscillogram voltage axis;

t is a waveform diagram time axis;

ton is the transistor on time of the high frequency switch circuit 10;

t is the switching time period of the high frequency switching circuit 10;

u (VO +, VO-) is the output voltage of the output rectifying and filtering circuit 30.

The duty ratio D of the high-frequency switching circuit 10 is defined as: d is Ton/T.

As can be seen from fig. 3, the voltage directions of the first primary winding N1 and the fourth secondary winding N4 are opposite, that is, the current input terminal of the first primary winding N1 and the current output terminal of the fourth secondary winding N4 are opposite terminals, and in this case, are flyback-connected (that is, the end with the origin on N1 and the end without the origin on N2 in fig. 1 are opposite terminals). As can be seen from fig. 4, when the output terminal of the output rectifying and filtering circuit 30 is short-circuited (i.e., (VO +, VO-) in fig. 1 is short-circuited), the output voltage of U (VO +, VO-) is zero, and the feedback control circuit 50 cannot be powered.

On the basis of the flyback switching power supply conversion circuit in the prior art, a forward auxiliary winding N3 and a forward auxiliary winding rectification circuit 73 are arranged, wherein the current output end of the forward auxiliary winding N3 and the current input end of the N1 are the same-name ends.

Referring to fig. 5, fig. 5 is a block diagram of a flyback switching power converter circuit according to a first embodiment of the present invention, which includes a high-frequency switching circuit 10, a transformer 20, an output rectifying and filtering circuit 30, a switching control circuit 40, and a feedback control circuit 50, where an output terminal of the output rectifying and filtering circuit 30 is connected to an input terminal and a power terminal of the feedback control circuit 50, the feedback control circuit 50 feeds back a control signal to the switching control circuit 40 through two ends OP1A and OP1B of an optocoupler, and an output terminal of the switching control circuit 40 is connected to a control terminal of the high-frequency switching circuit 10; a forward auxiliary winding rectifying circuit 73;

the forward auxiliary winding rectifier circuit 73 includes: the output end of the forward auxiliary winding rectifying circuit 73 is connected with the power supply end of the feedback control circuit 50 and is used for supplying power to the feedback control circuit 50 when the output end of the output rectifying and filtering circuit 30 is short-circuited.

In consideration of the fact that the output end of the output rectifying and filtering circuit 30 in the prior art cannot supply power to the feedback control circuit 50 when the output end of the output rectifying and filtering circuit 30 is short-circuited, the feedback control circuit 50 cannot monitor the output voltage and the output current of the output rectifying and filtering circuit 30 in real time.

In order to solve the above technical problem, the design idea of the present application provides a power supply module for the feedback control circuit 50, and when the output end of the output rectifying and filtering circuit 30 is short-circuited, the power supply module can still supply power to the feedback control circuit 50 to ensure that the feedback control circuit 50 can always work to collect the output state of the output rectifying and filtering circuit 30 and feed back the output state to the switch control circuit 40, thereby realizing the closed-loop control of the switching power supply.

Based on this, the present application provides a forward auxiliary winding rectifying circuit 73, which includes a forward auxiliary winding (the fifth secondary winding N5) and a first rectifying module, wherein the first rectifying module is configured to rectify the voltage on the forward auxiliary winding from ac to dc and output the dc to power the feedback control circuit 50. Wherein the turn ratio of the first primary winding N1 of the transformer 20 and the forward auxiliary winding N5 is positively correlated with the output voltage of the forward auxiliary winding rectifying circuit 73. When the output end of the output rectifying and filtering circuit 30 is short-circuited, U (VO +, VO-) is zero, and at this time, the voltage output by the forward auxiliary winding rectifying circuit 73 through the first rectifying module can be adjusted by adjusting the number of turns of the forward auxiliary winding N5, so that the voltage output by the forward auxiliary winding rectifying circuit 73 is used for supplying power to the feedback control circuit 50.

It should be noted that, when the output voltages of the forward auxiliary winding rectifying circuit 73 and the output rectifying and filtering circuit 30 are used to supply power to the feedback control circuit 50, when the conversion circuit is in normal operation (that is, when the output end of the output rectifying and filtering circuit 30 is not short-circuited), the output voltage of the forward auxiliary winding rectifying circuit 73 can be adjusted to be smaller than the output voltage of the output rectifying and filtering circuit 30 by adjusting the number of turns of the forward auxiliary winding, so that the feedback control circuit 50 is supplied with power by the output voltage of the output rectifying and filtering circuit 30. For example, when the output voltage of the output rectifying/smoothing circuit 30 is adjusted to 12V during normal operation of the converter circuit, the output voltage of the forward auxiliary winding rectifying circuit 73 may be adjusted to 7V. That is, when the converter circuit normally operates, the output voltage of the output rectifying and smoothing circuit 30 is used to supply power to the feedback control circuit 50, and the forward auxiliary winding rectifying circuit 73 has no actual current output and no loss. When the output end of the output rectifying and filtering circuit 30 is short-circuited, the feedback control circuit 50 is powered by the forward auxiliary winding rectifying circuit 73, so that the feedback control circuit 50 works normally.

In addition, the number of turns of the forward auxiliary winding in the present application is not particularly limited as long as power supply to the feedback control circuit 50 can be realized.

In addition, Rs in fig. 5 is a sampling resistor, and is configured to collect the output current of the output rectifying and filtering circuit 30, convert the current into a voltage value, and send the voltage value to the feedback control circuit 50, where the feedback control circuit 50 also collects the output voltage of the output rectifying and filtering circuit 30.

In summary, the forward auxiliary winding rectifying circuit 73 in the present application can make the feedback control circuit 50 continuously in a charged state, so that the feedback control circuit 50 can work all the time, and an extra transformer 20 is not needed, which is an isometric device with a large volume and a high cost, thereby reducing the cost and the volume of the switching power supply, increasing the application scenarios of the switching power supply, and meeting the industry technology development trend of increasing the power density of the power supply.

On the basis of the above-described embodiment:

referring to fig. 6, fig. 6 is a block diagram of a flyback switching power converter circuit according to a second embodiment of the present invention.

As a preferred embodiment, when the output voltage of the output rectifying and smoothing circuit 30 is not within the voltage range required by the power supply terminals of the feedback control circuit 50, the converter circuit further includes a flyback auxiliary winding rectifying circuit 72;

the flyback auxiliary winding rectification circuit 72 includes: the output end of the flyback auxiliary winding rectifying circuit 72 is connected with the power supply end of the feedback control circuit 50, and is used for supplying power to the feedback control circuit 50 when the output end of the output rectifying and filtering circuit 30 has no short circuit.

The present application aims to provide another power supply mode of the feedback control circuit 50, specifically, when the converter circuit further includes a flyback auxiliary winding rectifying circuit 72, wherein the output voltage of the flyback auxiliary winding rectifying circuit 72 is in positive correlation with the turn ratio of the first primary winding N1 and the flyback auxiliary winding (the fourth secondary winding N4) of the transformer 20. When the output end of the output rectifying and filtering circuit 30 is not short-circuited, because the output ends of the forward auxiliary winding rectifying circuit 73 and the flyback auxiliary winding rectifying circuit 72 are both connected with the power supply end of the feedback control circuit 50, at this time, if the output voltage of the flyback auxiliary winding rectifying circuit 72 is greater than the output voltage of the forward auxiliary winding rectifying circuit 73, the transformer 20 supplies power to the feedback control circuit 50 through the flyback auxiliary winding rectifying circuit 72; if the output voltage of the forward auxiliary winding rectifying circuit 73 is greater than the output voltage of the flyback auxiliary winding rectifying circuit 72, the transformer 20 supplies power to the feedback control circuit 50 through the forward auxiliary winding rectifying circuit 73; therefore, the output voltages of the flyback auxiliary winding rectifying circuit 72 and the forward auxiliary winding rectifying circuit 73 can be adjusted by adjusting the turn ratio of the first primary winding N1 to the flyback auxiliary winding and the turn ratio of the first primary winding N1 to the forward auxiliary winding of the transformer 20, so that when the output end of the output rectifying and filtering circuit 30 is not short-circuited, the flyback auxiliary winding rectifying circuit 72 is used for supplying power to the feedback control circuit 50, and at this time, the forward auxiliary winding rectifying circuit 73 does not output actual current and has no loss. When the output end of the output rectifying and filtering circuit 30 is short-circuited, the output voltage of the flyback auxiliary winding rectifying circuit 72 is zero, and the feedback control circuit 50 is powered by the forward auxiliary winding rectifying circuit 73. For example, when the output terminal of the output rectifying/smoothing circuit 30 is not short-circuited, the output voltage of the forward auxiliary winding rectifying circuit 73 may be adjusted to 7V, and the output voltage of the flyback auxiliary winding rectifying circuit 72 may be adjusted to 10V.

Specifically, referring to fig. 7, fig. 7 is a schematic waveform diagram of output voltages of the first primary winding, the fourth secondary winding and the fifth secondary winding when the output end of the output rectifying and filtering circuit provided by the present invention has no short circuit;

referring to fig. 8, fig. 8 is a schematic waveform diagram of output voltages of the output rectifying filter circuit, the flyback auxiliary winding rectifying circuit and the forward auxiliary winding rectifying circuit when there is no short circuit at the output end of the output rectifying filter circuit according to the present invention; here, the output voltage of the flyback auxiliary winding rectification circuit 72 decreases at the transistor on time in the high-frequency switch circuit 10, and the output voltage of the flyback auxiliary winding rectification circuit 72 increases at the transistor off time in the high-frequency switch circuit 10. The dotted line in the figure indicates that the forward auxiliary winding rectifying circuit 73 does not have an actual output voltage.

Referring to fig. 9, fig. 9 is a schematic waveform diagram of output voltages of the first primary winding, the fourth secondary winding and the fifth secondary winding when the output end of the output rectification filter circuit provided by the present invention is short-circuited;

referring to fig. 10, fig. 10 is a schematic waveform diagram of output voltages of the output rectifying filter circuit, the flyback auxiliary winding rectifying circuit and the forward auxiliary winding rectifying circuit when the output terminal of the output rectifying filter circuit is short-circuited. Here, the output voltage of the forward auxiliary winding rectifying circuit 73 increases at the transistor on time in the high-frequency switching circuit 10, and the output voltage of the forward auxiliary winding rectifying circuit 73 decreases at the transistor off time in the high-frequency switching circuit 10. The dotted line portion in the figure is an output voltage of the flyback auxiliary winding rectifier circuit 72.

Wherein v is the oscillogram voltage axis;

t is a waveform diagram time axis;

ton is the transistor on time in the high frequency switch circuit 10;

t is the switching time period of the high frequency switching circuit 10;

the duty ratio D of the high-frequency switching circuit 10 is defined as: d is Ton/T;

u (VO +, VO-) is the output end voltage of the output rectifying and filtering circuit 30;

u (72) (V2-1, SGND) is the calculated output voltage of the flyback auxiliary winding rectifying circuit 72;

u (73) (V2-1, SGND) is the calculated output voltage of the forward auxiliary winding rectifying circuit 73;

u (V2-1, SGND) is the actual output voltage at the output connection of the flyback auxiliary winding rectifier circuit 72 and the forward auxiliary winding rectifier circuit 73.

U (N1+, N1-) is the voltage on the first primary winding N1;

u (N2+, N2-) is the voltage on the second secondary winding N2;

u (N4+, N4-) is the voltage on the fourth secondary winding N4;

u (N5+, N5-) is the voltage on the fifth secondary winding N5.

According to the operating principle of the flyback switching power supply, in an ideal state (ignoring actual line loss and rectifier diode loss, and having no influence on analyzing the principle of the present invention), the calculation formula of the output voltage of the flyback auxiliary winding rectifying circuit 72 is as follows:

equation 1: u (VO +, VO-) ═ D n1 · U (VI +, VI-)/(1-D);

equation 2: u (72) (V2-1, SGND) ═ D × n2 × U (VI +, VI-)/(1-D);

equation 3 can be derived from equation 1 and equation 2, and specifically equation 3 is:

equation 3: u (72) (V2-1, SGND) ═ n2 × U (VO +, VO-)/n 1;

where N1 in equations 1, 2 and 3 is the turn ratio of the fourth secondary winding N4 and the first primary winding N1 in the transformer 20, and N2 is the turn ratio of the second secondary winding N2 and the first primary winding N1.

As can be seen from equation 3, n1 and n2 are coil turns ratios and are fixed constants, so the output voltage U (72) (V2-1, SGND) of the flyback auxiliary winding rectifier circuit 72 is proportional to the output voltage U (VO +, VO-) of the output rectifying and smoothing circuit 30. When U (VO +, VO-) is short-circuited, and the voltage of U (VO +, VO-) is close to 0V, the output voltage U (V2-1, SGND) of the flyback auxiliary winding rectifier circuit 72 is also close to 0V according to equation 3. That is, if only the flyback auxiliary winding rectifying circuit 72 is used to supply power to the feedback control circuit 50, or the output voltages of the flyback auxiliary winding rectifying circuit 72 and the output rectifying and filtering circuit 30 are used to supply power to the feedback control circuit 50, when the output terminal of the output rectifying and filtering circuit 30 is short-circuited, that is, U (VO +, VO-) is short-circuited, the feedback control circuit 50 will not have a power supply, and thus the switching power supply output terminal short-circuit constant current function cannot be realized. U (72) (V2-1, SGND) and U (V2-1, SGND) are both zero as in FIG. 4.

To sum up, by connecting the output end of the flyback auxiliary winding rectifying circuit 72 with the output end of the forward auxiliary winding rectifying circuit 73, when there is no short circuit at the output end of the output rectifying and filtering circuit 30, the output voltage of the flyback auxiliary winding rectifying circuit 72 can be made greater than the output voltage of the forward auxiliary winding rectifying circuit 73 by adjusting the number of turns of the turn ratio of the first primary winding N1 to the flyback auxiliary winding and the number of turns of the turn ratio of the first primary winding N1 to the forward auxiliary winding of the transformer 20, so that the forward auxiliary winding rectifying circuit 73 has no actual output current, and the power consumption is reduced; when the output end of the output rectifying and filtering circuit 30 is short-circuited, the forward auxiliary winding rectifying circuit 73 is used to supply power to the feedback control circuit 50, so that the feedback control circuit 50 is continuously powered.

As a preferred embodiment, the conversion circuit further includes a fourth diode D4;

the anode of the fourth diode D4 is connected to the output terminal of the output rectifying and smoothing circuit 30, and the cathode of the fourth diode D4 is connected to the power supply terminal of the feedback control circuit 50.

When the output terminal of the output rectifying and filtering circuit 30 is connected to the output terminal of the flyback auxiliary winding rectifying circuit 72 or the output terminal of the forward auxiliary winding rectifying circuit 73 and the power supply terminal of the feedback control circuit 50, if the output voltage of the output rectifying and filtering circuit 30 is not within the working range of the feedback control circuit 50 (the output terminal of the output rectifying and filtering circuit 30 may not be short-circuited, but when the flyback auxiliary winding rectifying circuit 72 is used to supply power to the feedback control circuit 50, the output terminal of the output rectifying and filtering circuit 30 may also be short-circuited, and when the forward auxiliary winding rectifying circuit 73 is used to supply power to the output rectifying and filtering circuit 30). At this time, in order to prevent the power supply, which is supplied by the flyback auxiliary winding rectifying circuit 72 or the forward auxiliary winding rectifying circuit 73 to the feedback control circuit 50, from flowing backward to the output rectifying and filtering circuit 30, so that the flyback switching power supply conversion circuit is damaged or the load connected with the flyback switching power supply conversion circuit is damaged, in the embodiment, the fourth diode D4 is provided by using the unidirectional conductivity of the diode. Specifically, when the output rectifying and smoothing circuit 30 supplies power to the feedback control circuit 50, the fourth diode D4 is turned on, and the output rectifying and smoothing circuit 30 supplies power to the feedback control circuit 50 through the fourth diode D4; when the flyback auxiliary winding rectifying circuit 72 or the forward auxiliary winding rectifying circuit 73 supplies power to the feedback control circuit 50, the fourth diode D4 is cut off, and the power output by the flyback auxiliary winding rectifying circuit 72 or the forward auxiliary winding rectifying circuit 73 cannot flow backward to the output rectifying and filtering circuit 30, so that the converter circuit is prevented from being damaged, and the working reliability of the flyback switching power supply converter circuit is ensured.

As a preferred embodiment, the conversion circuit further includes a voltage stabilizing circuit 71;

the forward auxiliary winding rectifying circuit 73 is connected with the output end of the flyback auxiliary winding rectifying circuit 72 as a first node, the input end of the voltage stabilizing circuit 71 is connected with the first node, and the output end of the voltage stabilizing circuit 71 is connected with the power supply end of the feedback control circuit 50, and is used for stabilizing the voltage of the first node at a fixed value to supply power to the feedback control circuit 50.

Considering that the voltages output by the forward auxiliary winding rectifying circuit 73 and the flyback auxiliary winding rectifying circuit 72 are rectified and filtered by the transformer 20, the average value of the voltages will vary with the output voltage value, the load size, and the ac input voltage value of the switching power supply, and thus the power supply voltage of the feedback control circuit 50 will be unstable.

In order to solve the above technical problem, the present application further provides a voltage stabilizing circuit 71 at the output end of the flyback auxiliary winding rectifying circuit 72 and the forward auxiliary winding rectifying circuit 73 to stabilize the corresponding output voltage, and at this time, the corresponding output voltage is stabilized within a certain range, and is a reliable power supply, so that the reliable power supply is used to supply power to the feedback control circuit 50, and the reliability of the power supply voltage of the feedback control circuit 50 is ensured. Wherein the first node is V2-1 in each graph.

As a preferred embodiment, the voltage stabilizing circuit 71 includes a sixth resistor R6, a controllable switch Q1, a zener diode DZ1, and a fifth capacitor C5;

a first end of the sixth resistor R6 is connected to the first end of the controllable switch Q1 and the first node, a second end of the sixth resistor R6 is connected to the cathode of the zener diode DZ1 and the control end of the controllable switch Q1, an anode of the zener diode DZ1 is connected to the first end of the fifth capacitor C5 and the ground, and a second end of the fifth capacitor C5 is connected to the second end of the controllable switch Q1 and the power supply terminal of the feedback control circuit 50.

Referring to fig. 11, fig. 11 is a schematic circuit diagram of a voltage regulator circuit 71 according to the present invention. The zener diode DZ1 plays a role of voltage stabilization, and when the output voltages of the flyback auxiliary winding rectification circuit 72 and the forward auxiliary winding rectification circuit 73 fluctuate, the voltage can be stabilized at a fixed value by the voltage stabilizing circuit 71 in this embodiment to supply power to the feedback control circuit 50. Specifically, the zener diode DZ1 in the present application stabilizes the voltage of the first node at about 7-20V, and may stabilize the voltage at other voltage values according to actual requirements, which is not limited herein. The controllable switch Q1 in this application may be, but is not limited to, an NPN (negative-positive-negative) transistor, where a base of the NPN transistor is a control terminal of the controllable switch Q1, an emitter of the NPN transistor is connected to the power supply terminal of the node 50, and a collector of the NPN transistor is connected to the first node, and the NPN transistor may also be another controllable switch, which is not limited herein.

In summary, the specific implementation manner of the voltage regulator circuit in this embodiment can stabilize the output voltage of 72 or 73 at a fixed value, so as to stabilize the power supply voltage of 50.

As a preferred embodiment, the forward auxiliary winding rectifying circuit 73 includes a fifth secondary winding N5, a second diode D2, a third diode D3 and a first inductor L1;

relative to the first primary winding N1, the synonym terminal of the fifth secondary winding N5 is connected to the cathode of the second diode D2, the synonym terminal of the fifth secondary winding N5 is connected to the cathode of the third diode D3 and the first terminal of the first inductor L1, the anode of the second diode D2 is connected to the anode of the third diode D3 and the ground, and the second terminal of the first inductor L1 is connected to the first node;

the turn ratio of the first primary winding N1 to the fifth secondary winding N5 and the inductance of the first inductor L1 are related to the output voltage of the forward auxiliary winding rectifying circuit 73.

Specifically, the present embodiment aims to provide a specific implementation manner of the forward auxiliary winding rectification circuit 73, please refer to fig. 12, and fig. 12 is a circuit schematic diagram of a first forward auxiliary winding rectification circuit according to the present invention. The second diode D2 and the third diode D3 rectify the voltage across the fifth secondary winding N5, and the third diode D3 is also a freewheeling diode of the first inductor L1. Referring to fig. 13, fig. 13 is a circuit schematic diagram of a second forward auxiliary winding rectifier circuit according to the present invention.

For a specific implementation manner of the forward auxiliary winding rectification circuit 73 in this embodiment, the forward auxiliary winding rectification circuit 73 may further include: r2, R3, R5, C3, C4; the connection relationship can be that R2 and C3 are connected in series and then connected in parallel with a second diode D2, R3 and C4 are connected in series and then connected in parallel with D3, one end of R5 is connected with the cathode of a third diode D3, and the other end is grounded. Referring to fig. 14, fig. 14 is a circuit schematic diagram of a third forward auxiliary winding rectifying circuit provided in the present invention. The connection relation of R2, R3, R5, C3 and C4 can also be as follows: r2 and C3 are connected in series and then connected in parallel with D2, R3 and C4 are connected in series and then connected in parallel with D3, one end of R5 is connected with the other end of the first inductor L1, and the other end of R5 is used as the output end of the forward auxiliary winding rectifying circuit 73, namely, is connected with the first node.

In summary, the forward auxiliary winding rectifying circuit 73 can be realized in a simple and reliable manner at any time.

Of course, the specific implementation of the forward auxiliary winding rectifying circuit 73 is not limited to the above example, and other implementations are possible as long as the function of the forward auxiliary winding rectifying circuit 73 can be realized, and the present application is not limited thereto.

relative to the first primary winding N1, the dotted terminal of the fifth secondary winding N5 is connected to the anode of the second diode D2, the dotted terminal of the fifth secondary winding N5 is connected to the anode of the third diode D3 and ground, the cathode of the second diode D2 is connected to the cathode of the third diode D3 and the first terminal of the first inductor L1, and the second terminal of the first inductor L1 is connected to the first node;

Specifically, the present embodiment aims to provide another specific implementation manner of the forward auxiliary winding rectification circuit 73, please refer to fig. 15, and fig. 15 is a circuit schematic diagram of a fourth forward auxiliary winding rectification circuit provided in the present invention. The second diode D2 and the third diode D3 rectify the voltage across the fifth secondary winding N5, and the third diode D3 is also a freewheeling diode of the first inductor L1.

In addition, on the basis of the fourth implementation manner of the forward auxiliary winding rectification circuit 73, please refer to fig. 16, and fig. 16 is a circuit schematic diagram of a fifth forward auxiliary winding rectification circuit according to the present invention.

The forward auxiliary winding rectifying circuit 73 may further include R2, R3, R5, C3, and C4; the connection relationship can be as follows: r2 is connected in series with C3 and then connected in parallel with D2, R3 is connected in series with C4 and then connected in parallel with D3, one end of R5 is connected with the other end of the first inductor L1, and the other end of R5 is used as the output end of the forward auxiliary winding rectifying circuit 73, namely, is connected with the first node.

Referring to fig. 17, fig. 17 is a schematic circuit diagram of a sixth forward auxiliary winding rectifier circuit according to the present invention.

In this case, the forward auxiliary winding rectifier circuit 73 further includes R2, R3, R5, C3, and C4;

the connection relationship can also be as follows: r2 and C3 are connected in series and then connected in parallel with a second diode D2, R3 and C4 are connected in series and then connected in parallel with D3, one end of R5 is connected with the cathode of a third diode D3, and the other end of R5 is grounded.

For a specific implementation manner of the first to sixth forward auxiliary winding rectifying circuits 73, it should be noted that the current input end of the first primary winding N1 and the current output end of the fifth secondary winding N5 are the same-name ends, the output voltage of the forward auxiliary winding rectifying circuit 73 is in positive correlation with the turn ratio of the fifth secondary winding N5 and the first primary winding N1, and is in negative correlation with the inductance of the first inductor L1, and the fifth secondary winding N5 is the forward auxiliary winding in the above embodiment.

Specifically, when the inductance of the first inductor L1 is selected to be sufficiently large, the output voltage of the forward auxiliary winding rectifying circuit 73 approaches the average value, and the calculation formula is as follows:

equation 4: u (73) (V2-1, SGND) (average) D n 3U (VI +, VI-);

when the inductance of the first inductor L1 is selected to be sufficiently small and the load current of the control circuit is small, the output voltage of the forward auxiliary winding rectifying circuit 73 approaches the peak value, and the calculation formula is as follows:

equation 5: u (73) (V2-1, SGND) (peak) n3 × U (VI +, VI-);

where U (73) (V2-1, SGND) is the calculated output voltage of the forward auxiliary winding rectifying circuit 73, and N3 is the ratio of the number of turns of the fifth primary winding N1 to the number of turns of the fifth secondary winding N5.

As can be seen from the above two equations, the output voltage of the forward auxiliary winding rectifying circuit 73 is positively correlated with n3 and the input voltage of the converter circuit, and is not correlated with the output voltage U (VO +, VO-) of the output rectifying and smoothing circuit 30, and when the duty ratio is not zero, the output voltage of the forward auxiliary winding rectifying circuit 73 is not zero even if the output terminal of the output rectifying and smoothing circuit 30 is short-circuited, and the output voltage of the forward auxiliary winding rectifying circuit 73 can be changed between the average value and the peak value by adjusting the inductance value of the first inductor L1. Referring to fig. 9 and 10, it can be seen that the output voltage of the forward auxiliary winding rectifying circuit 73 is not zero, and can be implemented to supply power to the feedback control circuit 50. In summary, the forward auxiliary winding rectification circuit 73 in this embodiment can be implemented to supply power to the feedback control circuit 50 when the output terminal of the output rectification filter circuit 30 is short-circuited, and the implementation manner is simple and reliable.

As a preferred embodiment, the flyback auxiliary winding rectification circuit 72 includes a fourth secondary winding N4, a first diode D1, and a first capacitor C1;

relative to the first primary winding N1, the dotted terminal of the fourth secondary winding N4 is connected to the cathode of the first diode D1, the different-dotted terminal of the fourth secondary winding N4 is connected to the first terminal and the first node of the first capacitor C1, and the other terminal of the first capacitor C1 is connected to the anode of the fifth diode and ground;

the turn ratio of the first primary winding N1 to the fourth secondary winding N4 is related to the output voltage of the flyback auxiliary winding rectifier circuit 72.

Referring to fig. 18, fig. 18 is a schematic circuit diagram of a flyback auxiliary winding rectifier circuit 72 according to a first embodiment of the present invention. The current output end of the fourth secondary winding N4 and the current input end of the first primary winding N1 are opposite terminals. The output voltage of the flyback auxiliary winding rectifying circuit 72 is in positive correlation with the turn ratio of the fourth secondary winding N4 to the first primary winding N1, and the output voltage of the forward auxiliary winding rectifying circuit 73 can be adjusted by adjusting the turn ratio. The fourth secondary winding N4 is the flyback auxiliary winding in the above embodiment.

On the basis of the specific implementation of the flyback auxiliary winding rectification circuit 72, please refer to fig. 19 and 20, fig. 19 is a circuit schematic diagram of a flyback auxiliary winding rectification circuit of a second kind provided by the present invention, and fig. 20 is a circuit schematic diagram of a flyback auxiliary winding rectification circuit of a third kind provided by the present invention.

The flyback auxiliary winding rectifying circuit 72 may further include R1, C1, C2 and R4, and the connection relationship may be: as shown in fig. 19, R1 is connected in series with C2 and then connected in parallel with D1, one end of R4 is connected to the synonym terminal of the fourth secondary winding N4, the other end of R4 is connected to the first node, one end of C1 is connected to the anode of the first diode D1, and the other end is connected to the first node. The connection relationship can also be as follows: as shown in fig. 20, R1 is connected in series with C2 and then connected in parallel with D1, one end of R4 is connected to the anode of the first diode D1, the other end of R4 is connected to one end of C1 and ground, respectively, and the other end of C1 is connected to the first node.

In summary, the flyback auxiliary winding rectifier circuit 72 in this embodiment can realize the function of the flyback auxiliary winding rectifier circuit 72, and the number and the volume of the used electronic devices are small.

Of course, the specific implementation manner of the flyback auxiliary winding rectification circuit 72 is not limited to the above example, and other implementation manners are also possible as long as the function of the flyback auxiliary winding rectification circuit 72 can be realized, and the present application is not particularly limited herein.

relative to the first primary winding N1, the synonym terminal of the fourth secondary winding N4 is connected to the anode of the first diode D1, the cathode of the first diode D1 is connected to the first terminal and the first node of the first capacitor C1, and the second terminal of the first capacitor C1 is connected to the synonym terminal of the fourth secondary winding N4 and ground;

Referring to fig. 21, fig. 21 is a schematic circuit diagram of a fourth flyback auxiliary winding rectifier circuit provided in the present invention. The current output end of the fourth secondary winding N4 and the current input end of the first primary winding N1 are opposite terminals. The output voltage of the flyback auxiliary winding rectifying circuit 72 is in positive correlation with the turn ratio of the fourth secondary winding N4 to the first primary winding N1, and the output voltage of the flyback auxiliary winding rectifying circuit 72 can be adjusted by adjusting the turn ratio. The fourth secondary winding N4 is the flyback auxiliary winding in the above embodiment.

Based on the specific implementation of the flyback auxiliary winding rectifier circuit 72 in this embodiment, please refer to fig. 22 and 23, fig. 22 is a circuit schematic diagram of a fifth flyback auxiliary winding rectifier circuit provided in the present invention, and fig. 23 is a circuit schematic diagram of a sixth flyback auxiliary winding rectifier circuit provided in the present invention.

The flyback auxiliary winding rectifying circuit 72 may further include R1, C1, C2 and R4, and the connection relationship may be: as shown in fig. 22, R1 is connected in series with C2 and then connected in parallel with D1, one end of R4 is connected to the end of the fourth secondary winding N4 with the same name, the other end of R4 is grounded, one end of C1 is connected to the cathode of the first diode D1, and the other end is connected to the first node. The connection relationship can also be as follows: as shown in fig. 23, R1 is connected in series with C2 and then connected in parallel with D1, one end of R4 is connected to the cathode of the first diode D1, the other end of R4 is connected to one end of C1 and the first node, respectively, and the other end of C1 is grounded.

As a preferred embodiment, the secondary auxiliary power module 70 includes a forward auxiliary winding rectifying circuit 73, a flyback auxiliary winding rectifying circuit 72 and a voltage stabilizing circuit 71, and the conversion circuit further includes a primary auxiliary power module 60;

the primary auxiliary power supply module 60 comprises a primary forward auxiliary winding rectifying circuit 63, a primary flyback auxiliary winding rectifying circuit 62 and a primary voltage stabilizing circuit 61;

the primary forward auxiliary winding rectifying circuit 63 and the forward auxiliary winding rectifying circuit 63 have the same structure; the primary flyback auxiliary winding rectifying circuit 62 and the flyback auxiliary winding rectifying circuit 62 have the same structure, and the primary voltage stabilizing circuit 61 and the voltage stabilizing circuit 61 have the same circuit structure;

the output terminal of the primary regulator 61 is connected to the power supply terminal of the switch control circuit 40 for supplying power to the switch control circuit 40.

Considering that the switch control circuit 40 in the conversion circuit also needs to supply power, as shown in V1 in fig. 6, a primary auxiliary power module 60 may be provided on the primary side of the transformer 20, wherein the circuit structure of the primary auxiliary power module 60 is identical to that of the secondary auxiliary power module 70, so as to ensure the power supply reliability of each module in the conversion circuit.

In addition, the primary auxiliary power module 60 may be, but is not limited to, set to supply power to the switch control circuit 40, the secondary auxiliary power module 70 may be, but is not limited to, only supply power to the feedback control circuit 50, and when there are other circuit structures in the conversion circuit or other modules that need to be supplied power in the application scenario, for example, a single chip and a control circuit of the power supply, a power failure monitoring circuit, a display circuit, and the like, the primary auxiliary power module 60 or the secondary auxiliary power module 70 may also be used to supply power thereto, and the application is not limited specifically herein.

It should be noted that the conversion circuit of the present invention can be applied to high-frequency switching power supplies with any appearance and structure; the method can be realized in any printed circuit board layout connection mode; the components in the conversion circuit of the invention can be any packaged components with the same principle and performance, and the serial connection and parallel connection combination thereof, and the application is not particularly limited.

It is to be noted that, in the present specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flyback switching power supply conversion circuit is characterized by comprising a high-frequency switching circuit, a transformer, an output rectifying filter circuit, a switching control circuit and a feedback control circuit, wherein the output end of the output rectifying filter circuit is connected with the input end and the power end of the feedback control circuit; the device also comprises a forward auxiliary winding rectifying circuit;

2. The flyback switching power converter circuit of claim 1, wherein the converter circuit further comprises a flyback auxiliary winding rectifier circuit when the output voltage of the output rectifying filter circuit is not within the voltage range required by the power terminals of the feedback control circuit;

3. The flyback switching power converter circuit of claim 2, wherein the converter circuit further comprises a fourth diode;

4. The flyback switching power converter circuit of claim 2, wherein the converter circuit further comprises a voltage regulator circuit;

5. The flyback switching power converter circuit of claim 4 wherein the voltage regulator circuit comprises a sixth resistor, a controllable switch, a zener diode, and a fifth capacitor;

6. The flyback switching power converter circuit of claim 1 wherein the forward auxiliary winding rectifier circuit comprises a fifth secondary winding, a second diode, a third diode, and a first inductor;

7. The flyback switching power converter circuit of claim 1 wherein the forward auxiliary winding rectifier circuit comprises a fifth secondary winding, a second diode, a third diode, and a first inductor;

8. The flyback switching power converter circuit of claim 6 or 7, wherein the flyback auxiliary winding rectifier circuit comprises a fourth secondary winding, a first diode, and a first capacitor;

9. The flyback switching power converter circuit of claim 6 or 7, wherein the flyback auxiliary winding rectifier circuit comprises a fourth secondary winding, a first diode, and a first capacitor;

10. The switching power conversion circuit according to claim 4, wherein the secondary auxiliary power module comprises the forward auxiliary winding rectifying circuit, the flyback auxiliary winding rectifying circuit and the voltage stabilizing circuit, and the conversion circuit further comprises the primary auxiliary power module;