CN112583275B

CN112583275B - Flyback multi-output power supply system and control circuit and power supply method thereof

Info

Publication number: CN112583275B
Application number: CN202011097348.9A
Authority: CN
Inventors: 俞秀峰; 林官秋; 叶俊
Original assignee: Shenzhen Biyi Microelectronics Co ltd
Current assignee: Shenzhen Biyi Microelectronics Co ltd
Priority date: 2020-10-14
Filing date: 2020-10-14
Publication date: 2023-02-17
Anticipated expiration: 2040-10-14
Also published as: CN112583275A

Abstract

The invention provides a flyback multi-output power supply system, a control circuit thereof and a power supply method. The flyback multiplexed output power supply system comprises: a primary side circuit; the transformer comprises a primary winding and a secondary winding; the first output circuit provides a first output voltage and comprises a first one-way conduction device and a switching tube which are coupled with the secondary winding; a second output circuit providing a second output voltage comprising a second unidirectional conducting device coupled to the secondary winding; and the control circuit controls the switching tube to be in a turn-off state when the primary side switch is turned off, and controls the switching tube to be switched on when the first output voltage is detected to be smaller than a preset threshold value. The multi-output power supply system, the control circuit and the power supply method thereof can be used for accurately controlling the multi-output, and the system has a simple structure and higher efficiency.

Description

Flyback multi-output power supply system and control circuit and power supply method thereof

Technical Field

The invention relates to the field of electronics, in particular to a flyback multi-output power supply system, a control circuit thereof and a power supply method thereof.

Background

In electronic power supply systems, it is often necessary to provide different power supply sources for different loads in the system. In the field of home appliances, for example, different power supplies are required for different components, such as motors, processing units, etc. One conventional method is to provide independent power supplies for different loads, but this method has a low integration level and a high system power cost. In order to improve the integration degree of a power supply system and reduce the cost of a power supply source, the requirement for a multi-output power supply system is provided.

In a conventional multi-output power supply system, a main circuit output and a sub circuit output are often arranged in a voltage conversion circuit system. The main path output is provided by a conventional voltage conversion topology. The output of the auxiliary circuit is provided with a low dropout linear voltage regulator (LDO) at the output end of the main circuit. However, in this method, the LDO has high power consumption and low system efficiency due to a large output current and a large difference between the auxiliary output voltage value and the main output voltage value.

Another power supply method is to set two isolated output circuits on the secondary side of the isolated power supply, but because of the feedback problem, only one output voltage can be controlled. When the load change or overload occurs in the output of the path, the abnormal change of the output of the other path is often caused and the adjustment cannot be performed.

In view of the above, there is a need to provide a new structure or control method to solve at least some of the above problems.

Disclosure of Invention

The invention provides a flyback multi-output power supply system, a control circuit thereof and a power supply method thereof, aiming at one or more problems in the prior art.

According to a first aspect of the present invention, a flyback multiple-output power supply system includes: a primary side circuit including a primary side switch; the transformer comprises a primary winding and a secondary winding, wherein the primary winding is coupled with the primary switch; the first output circuit comprises a first one-way conduction device and a switching tube which are coupled with the secondary winding and connected in series, and the first output circuit provides a first output voltage at a first output end; a second output circuit comprising a second unidirectional conducting device coupled to the secondary winding, the second output circuit providing a second output voltage at a second output terminal, wherein the second output voltage is greater than the first output voltage; and the control circuit is provided with a signal input end and an output end, wherein the signal input end of the control circuit is coupled with the first output end, the output end of the control circuit is coupled with the control end of the switching tube and used for controlling the switching-on and the switching-off of the switching tube, when the primary side switch is switched off, the control circuit controls the switching tube to be in a switching-off state, and when the first output voltage is detected to be smaller than a preset threshold value, the control circuit controls the switching tube to be switched on.

In one embodiment, the multi-output power supply system controls the switching tube to be switched off during the period that the primary side switch is switched on.

In one embodiment, the multiple output power supply system further comprises: the isolated feedback loop detects the second output voltage to generate a feedback signal; and the primary side control circuit is coupled with the primary side switch and controls the primary side switch based on the feedback signal.

In one embodiment, the control circuit includes a comparison circuit for comparing a sampling signal indicative of the first output voltage with a threshold signal, wherein the switching tube is in an off state when the primary switch is off, and the control circuit turns on the switching tube when the control circuit detects that the sampling signal is less than the threshold signal.

In one embodiment, the control circuit further includes a window time control circuit, an input terminal of the window time control circuit is coupled to one end of the switching tube, and the window time control circuit detects a time point of the switching on or off of the primary side switch based on a terminal voltage of the switching tube, and turns off the switching tube after a preset window time of the switching on or off of the primary side switch.

In one embodiment, the control circuit includes: the comparator circuit is provided with a non-inverting input end, an inverting input end and an output end, wherein the non-inverting input end of the comparator circuit receives a threshold signal, and the inverting input end of the comparator circuit is coupled with the first output end and used for receiving a sampling signal; the window time control circuit is provided with an input end and an output end, and the input end of the window time control circuit is coupled with one end of the switching tube; the trigger circuit is provided with a set input end, a reset input end and an output end, wherein the set input end is coupled with the output end of the comparison circuit, and the reset input end is coupled with the output end of the window time control circuit; and the input end of the driving circuit is coupled with the output end of the trigger circuit, and the output end of the driving circuit is coupled with the control end of the switch tube.

In one embodiment, the first unidirectional device comprises a first diode, the second unidirectional device comprises a second diode, an anode terminal of the first diode is coupled to an anode terminal of the second diode and further coupled to a first terminal of the secondary winding, a second terminal of the secondary winding is coupled to a reference ground of the secondary winding, a cathode terminal of the first diode is coupled to a first terminal of the switching tube, a second terminal of the switching tube is coupled to the first output terminal, and a cathode terminal of the second diode is coupled to the second output terminal.

In one embodiment, the secondary winding includes a first secondary winding and a second secondary winding, wherein the first secondary winding is coupled to the first unidirectional conducting device and the second secondary winding is coupled to the second unidirectional conducting device.

In one embodiment, the second output voltage is used to power the control circuit.

According to another aspect of the present invention, a control circuit for a flyback multi-output power supply system, wherein the flyback multi-output power supply system provides a first output voltage at a first output terminal of a secondary side and a second output voltage at a second output terminal, the control circuit has a signal input terminal and an output terminal, wherein the signal input terminal of the control circuit is coupled to the first output terminal for obtaining a sampling signal representing the first output voltage, and the output terminal of the control circuit is coupled to a control terminal of a switching tube for controlling the switching tube to be turned on and off, wherein the switching tube is coupled to the first output terminal, when a primary side switch is turned off, the switching tube is in an off state, and when the first output voltage is smaller than a preset threshold, the control circuit controls the switching tube to be turned on.

In one embodiment, the control circuit includes a comparison circuit, an input terminal of the comparison circuit receives a sampling signal representing the first output voltage and a threshold signal, and an output terminal of the comparison circuit is coupled to the control terminal of the switching tube.

According to another aspect of the present invention, a power supply method for providing multiple outputs in a flyback voltage converter circuit includes: the first one-way conduction device and the switch tube are connected in series and coupled with an auxiliary winding of the flyback voltage conversion circuit to provide a first output voltage; coupling a second unidirectional device to the secondary winding for providing a second output voltage; controlling a primary side switch of the flyback voltage conversion circuit based on the second output voltage; and controlling the switching tube to be switched off during the switching-on period of the primary side switch, and controlling the switching tube to be switched on when the first output voltage is smaller than a preset threshold value.

In one embodiment, the power supply method further comprises the steps of detecting the turn-off time point of the primary side switch based on the terminal voltage of the switching tube, and controlling the switching tube to be turned off after a preset window time.

In one embodiment, the window time is adjustable by an external device.

The multi-output power supply system, the control circuit and the power supply method thereof can be used for accurately controlling the multi-output, and the system has a simple structure and higher efficiency.

Drawings

Fig. 1 is a block diagram of a flyback multi-output power supply system according to an embodiment of the invention;

fig. 2 is a waveform diagram of a flyback multi-output power supply system according to an embodiment of the invention;

FIG. 3 is a circuit diagram of a flyback multiple output power supply system according to an embodiment of the present invention;

fig. 4 shows a schematic diagram of a control circuit for a flyback multi-output power supply system according to an embodiment of the invention;

fig. 5 is a flow chart illustrating a method for providing multiple outputs in a flyback voltage converter circuit according to an embodiment of the invention.

Detailed Description

For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.

The description in this section is for several exemplary embodiments only and the invention is not to be limited in scope by the embodiments described. Combinations of different embodiments, and substitutions of features from different embodiments, or similar prior art means may be substituted for or substituted for features of the embodiments shown and described.

The term "coupled" or "connected" in this specification includes both direct and indirect connections. An indirect connection is a connection made through an intermediary, such as a conductor, where the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or through an intermediary circuit or component as described in embodiments herein; indirect connections may also include connections through other active or passive devices that perform the same or similar function, such as connections through circuits or components such as signal amplification circuits, follower circuits, etc. "plurality" or "plurality" means two or more.

Fig. 1 is a circuit diagram of a flyback multi-output power supply system according to an embodiment of the invention. The flyback multi-output power supply system comprises a primary circuit, a transformer 12, a first output circuit 13, a second output circuit 14 and a control circuit 15. The first output circuit 13, the second output circuit 14 and the control circuit 15 are located on the secondary side of the flyback multiple output power supply system, and they obtain energy from the transformer 12, and provide at least two outputs on the secondary side for supplying power to at least two loads. The primary side circuit includes a primary side switch Q and a primary side control circuit 111. The primary circuit may further include a rectifying circuit 110 for rectifying and filtering the ac mains voltage Vac to convert it into a dc input voltage Vin. The transformer 12 includes a primary winding L1 and a secondary winding L2, wherein the primary winding L1 is coupled to a primary switch Q, and the power supply system transfers energy from the primary side to the secondary side through the transformer 12 by controlling the switching of the primary switch Q. The first output circuit 13 includes a first one-way conduction device D1 and a switch tube K connected in series and coupled to the secondary winding L2, and the first output circuit 13 provides a first output voltage Vout1 at a first output terminal of the multi-output power supply system. The second output circuit 14 comprises a second unidirectional conducting device D2 coupled to the secondary winding L2, the second output circuit 14 providing a second output voltage Vout2 at a second output terminal, wherein the second output voltage Vout2 is larger than the first output voltage Vout1. The dotted terminal of the primary winding L1 is coupled to the primary switch Q, and the dotted terminal of the primary winding receives the dc input voltage Vin. In one embodiment, the dc input voltage Vin is obtained by the rectifying and filtering circuit 110 based on the ac mains rectifying and filtering. The dotted terminal of the secondary winding L2 is coupled to the anode terminal of the first unidirectional conducting device D1 and the anode terminal of the second unidirectional conducting device D2, and the dotted terminal of the secondary winding L2 is connected to the secondary reference ground. In the illustrated embodiment, the first and second unidirectional conducting devices D1 and D2 are diodes. The cathode of the diode D1 is connected to the first end of the switching tube K, and the second end of the switching tube K is coupled to the first output capacitor C1 and is used for providing the first output voltage Vout1 at the first output terminal. The cathode of the diode D2 is coupled to the second output capacitor C2 and is used for providing the second output voltage Vout2 at the second output terminal. The control circuit 15 has a signal input terminal VS and an output terminal, wherein the signal input terminal of the control circuit 15 is coupled to the first output terminal Vout1 for obtaining a sampling signal VS representing the first output voltage Vout1, and the output terminal of the control circuit 15 is coupled to the control terminal of the switching tube K for controlling the switching tube K to be turned on and off. In one embodiment, the sampling signal VS is obtained by a resistor divider circuit coupled to the first output terminal Vout1. In another embodiment, the sampling signal VS is directly the first output voltage Vout1. Thus, the first output voltage Vout1 is controlled by controlling the on/off of the switch transistor K. While the second output voltage Vout2 is regulated by the primary side switch Q controlled by the isolation feedback loop 16. Therefore, the control of the two paths of output can be realized, and when one path of output is abnormal, the other path of output can still be effectively regulated.

In the illustrated embodiment, the first unidirectional conducting device D1 and the second unidirectional conducting device D2 are located at the side of the secondary winding at the output terminal, i.e., the high side, but the first unidirectional conducting device D1 and the second unidirectional conducting device D2 may also be located at the side of the secondary winding at the secondary reference ground, i.e., the low side.

In the illustrated embodiment, the anode of the first unidirectional conducting device D1 is coupled to the secondary winding of the transformer, the cathode of the first unidirectional conducting device D1 is coupled to the switching tube K, and the other end of the switching tube K is coupled to the first output capacitor C1 for providing the first output voltage. However, in another embodiment, the order of the switch tube K and the first unidirectional conducting device D1 may be interchanged.

The multiple output power supply system further comprises an isolation type feedback loop 16, wherein the feedback loop 16 detects the second output voltage Vout2 for generating a feedback signal FB; the primary side control circuit 111 is coupled to the primary side switch Q, and the primary side control circuit 111 controls the primary side switch Q based on the feedback signal FB to control the energy of the secondary side obtained by transmission, so as to control the second output voltage Vout2.

In the embodiment shown in fig. 1, the control circuit 15 includes a comparison circuit for comparing the sampling signal VS of the first output voltage Vout1 with the threshold signal Vth. When the primary side switch Q is turned off, the control circuit 15 controls the switching tube K to be in an off state, the system preferentially supplies power to the second output end Vout2, and at the moment, the voltage Vout2 rises, and Vout1 falls. When the control circuit 15 detects that the voltage Vout1 is too low, for example, the sampling signal VS is smaller than the threshold signal Vth or the sampling signal VS is smaller than the preset threshold and the slope is smaller than the slope threshold, the control circuit 15 turns on the switching tube K, and since the first output voltage Vout1 is lower than the second output voltage Vout2, the remaining energy in the secondary winding L2 will stop being supplied to the second output circuit 14 and all be supplied to the first output circuit 13, and the waveform diagram of the control process refers to fig. 2, where the first output voltage Vout1 rises at this time until the freewheeling current in the secondary winding becomes zero or the primary switch Q is turned on again. In one embodiment, when the primary switch Q is turned off, the control circuit 15 controls the switching tube K to be in an off state, including turning off the switching tube K during a period when the primary switch Q is turned on, for example, detecting a turn-on action of the primary switch Q by detecting a voltage at the terminal of the switching tube K, for example, determining that the primary switch is turned on when a source-drain voltage of the switching tube K is greater than a preset threshold, and turning off the switching tube K at this time.

In the embodiment shown in fig. 1, in which the transformer 12 comprises only one secondary winding L2, the first output circuit 13 and the second output circuit 14 share the secondary winding L2. Wherein the anode terminal of the first unidirectional conducting device D1 is coupled to the anode terminal of the second unidirectional conducting device D2 and further coupled to the first terminal (dotted terminal) of the secondary winding L2, the second terminal (dotted terminal) of the secondary winding L2 is coupled to the reference ground of the secondary, the cathode terminal of the first unidirectional conducting device D1 is coupled to the first terminal of the switching tube K, the second terminal of the switching tube K is coupled to the first output terminal Vout1, and the cathode terminal of the second unidirectional conducting device D2 is coupled to the second output terminal Vout2. However, the secondary winding may also comprise two, see fig. 3.

In one embodiment, the control circuit 15 further includes a window time control circuit (see fig. 4), which obtains a signal indicating that the primary switch Q is turned off based on the terminal voltage of the switching tube K, and sets a window time within a preset time when the primary switch Q is turned off, where the control circuit 15 controls the switching tube K to turn on the switching tube K only within the window time and to turn off the switching tube K at the end of the window time. In one embodiment, the window time is adjusted by adjusting the value of an external device, such as a resistor or capacitor.

Fig. 2 is a waveform diagram of a flyback multiple-output power supply system according to an embodiment of the invention. Referring to fig. 1, signals from top to bottom are a control signal PWM for controlling the primary side switch Q, a primary side current Ip flowing through the primary side winding, a secondary side current Is flowing through the secondary side winding, a switch control signal CTR for controlling the switching tube K, a first path of current Is1 flowing through the first diode D1, and a second path of current Is2 flowing through the second diode D2. At time t1, the PWM signal Is set high, the primary side switch Q Is switched on, the primary side current Ip rises, the secondary side diodes D1 and D2 are reversely biased to be cut off, and the secondary side current Is zero. At time t2, the primary switch Q Is turned off, the primary current Ip becomes zero, the voltage of the secondary winding L2 Is reversed, the secondary diodes D1 and D2 are forward-biased, the energy stored in the primary winding L1 Is released in the form of the secondary current Is through the secondary winding L2, and the secondary current Is the maximum value. At this time, the switch control signal CTR Is in a low level state, the switching tube K Is in an off state, the secondary current Is supplied to the second output circuit 13, and the second output voltage Vout2 rises. The first output voltage Vout1 drops in voltage during consumption. At time t3, when the first output voltage Vout1 is lower than the set threshold, the control circuit 15 controls the switch signal CTR to be high, the switch tube K is turned on, the residual energy on the secondary side of the flyback voltage conversion circuit is provided to the first output circuit 13, and the first output voltage Vout1 rises until the end of the freewheeling or the arrival of the next switching cycle. In one embodiment, the flyback voltage converter circuit employs a critical control mode (BCM) that turns on the primary switch Q when the secondary current drops to zero. At time t4, the PWM signal is again set high for turning on the primary switch Q and a new switching cycle begins. When the freewheeling is over, if the first output voltage Vout1 is lower, in the next cycle, it may cause the first output voltage Vout1 to be lower than the preset threshold earlier, the secondary freewheeling current supplies the first output circuit 13 earlier, so that the first output voltage increases, and if the first output voltage Vout is higher, in the next cycle, it may cause the first output circuit 13 to start to be supplied with power at a later time for lowering the first output voltage Vout1. Meanwhile, the second output voltage Vout2 is regulated by controlling the primary side switch Q through the isolation feedback loop 16 to further control the energy transferred to the secondary side by the primary side, and is stabilized at a preset level.

Fig. 3 is a circuit diagram of a flyback multi-output power supply system according to an embodiment of the invention. In contrast to the embodiment of fig. 1, the secondary winding of the transformer 32 of fig. 3 comprises a first secondary winding L2 and a second secondary winding L3. The first secondary winding L2 is coupled to the first unidirectional conducting device D1 for providing energy to the first output circuit 33, and the second secondary winding L3 is coupled to the second unidirectional conducting device D2 for providing energy to the second output circuit 34. In the illustrated embodiment, the first unidirectional conducting device D1 and the second unidirectional conducting device D2 are located on the side of the respective secondary windings near the output end, and are high-order rectifiers. In other embodiments, the first unidirectional conducting device D1 and/or the second unidirectional conducting device D2 may also be located on a side of the respective secondary winding near the reference ground, as a low-side rectifier. In the illustrated embodiment, the isolated feedback loop for providing the feedback signal FB comprises a signal processing circuit on the secondary side and an optocoupler, wherein the optocoupler comprises a light emitter on the secondary side and a light receiver on the primary side. In addition, referring to fig. 3, the control circuit 35 for controlling the switch K of the first output circuit 33 may further have a supply terminal VDD, wherein the supply terminal VDD is coupled to the output terminal of the second output circuit 34 for receiving the second output voltage Vout2, so that the second output voltage Vout2 is directly used for supplying power to the control circuit 35.

FIG. 4 shows a control circuit schematic according to an embodiment of the invention. The control circuit includes a comparison circuit 41, a window time control circuit 42, a logic circuit 43, and a drive circuit 44. The input terminal of the window time control circuit 42 is coupled to one terminal of the switching tube K for obtaining a voltage difference between two terminals of the switching tube K, and the output terminal of the window time control circuit 42 provides a turn-off signal. The terminal voltage of the switching tube includes a voltage of a first terminal (e.g., a Drain terminal Drain) of the switching tube and/or a voltage of a second terminal (e.g., a source terminal), and when the primary side switch Q is turned off, a difference between the voltage of the first terminal and the voltage of the second terminal is greater than a preset threshold. In one embodiment, the control circuit 15 obtains a signal indicating that the primary side switch Q is turned on based on the terminal voltage of the switching tube, and the control circuit 15 controls the switching tube K to turn off the switching tube K during the turn-on period of the primary side switch Q, for example, outputs a valid signal after detecting that the primary side switch Q is turned on or turned on for a predetermined time, so as to turn off the switching tube K. The logic circuit 43 may include an RS flip-flop circuit, wherein a non-inverting input of the comparison circuit 41 receives the threshold signal Vth, an inverting input of the comparison circuit 41 is coupled to a first output for receiving the sampling signal VS representing the first output voltage Vout1, an output of the comparison circuit 41 is coupled to a set input of the flip-flop circuit 43, and an output of the window time control circuit 42 is coupled to a reset input of the flip-flop circuit 43. The output terminal of the trigger circuit 43 is coupled to the input terminal of the driving circuit 44, and the output terminal of the driving circuit 44 is coupled to the control terminal of the switch K. When the comparison circuit 41 indicates that the first output voltage is smaller than the preset threshold, for example, the sampling signal VS is smaller than the threshold signal Vth, the comparison circuit 41 outputs an effective level, when the set input terminal of the trigger circuit 43 is an effective value, the RS trigger circuit 43 outputs an effective value, for example, a high level, and the switch driving signal CTR amplified by the driving circuit 44 is in a first state, so as to turn on the switching tube K. When the window time control circuit 42 provides an effective signal, that is, the reset input terminal of the trigger circuit 43 has an effective value, the output value of the RS trigger circuit 43 is in an invalid state, for example, low level, and the switch driving signal CTR is in a second state, so as to turn off the switch transistor K. In one embodiment, the switch transistor K includes an N-type MOSFET (metal oxide semiconductor field effect transistor), and the switch transistor K is turned on when the driving signal CTR is a higher voltage; when the driving signal CTR is at a low voltage, the switching tube K is turned off.

Fig. 5 is a flow chart illustrating a method for providing multiple outputs in a flyback voltage converter according to an embodiment of the present invention. The method includes coupling a first unidirectional conducting device D1 and a switching tube K in series with a secondary winding of a flyback voltage conversion circuit for providing a first output voltage Vout1 at step 501. In one embodiment, the first unidirectional device D1 includes a first diode D1 having an anode coupled to the secondary winding and a cathode coupled to a switch K, the other end of the switch K being coupled to a first output terminal, and the first output terminal providing the first output voltage Vout1. The method includes coupling a second unidirectionally conducting device D2 with the secondary winding for providing a second output voltage Vout2 at step 502, wherein the second output voltage Vout2 is higher than the first output voltage Vout1. In one embodiment, the second unidirectional device D2 includes a second diode having an anode coupled to the secondary winding and a cathode coupled to a second output terminal providing the second output voltage. The first one-way conduction device and the second one-way conduction device can be coupled with the same end of the same secondary winding and can also be coupled with different secondary windings. The method includes controlling a primary switch Q of the flyback voltage conversion circuit based on the second output voltage Vout2 at step 503. In one embodiment, the system feeds back the second output voltage Vout2 to the primary side through a secondary side feedback circuit and an optocoupler to control the primary side switch Q. Wherein the secondary feedback circuit may comprise a controllable precision voltage regulator TL431 known to those skilled in the art. The method further includes controlling the switching tube K to turn off during the turn-on period of the primary side switch, such that when the primary side switch Q turns off, the secondary side winding starts freewheeling, since the switching tube K is in the off state, the freewheeling current flows to the second output circuit first, the second output voltage Vout2 rises, and the first output voltage Vout1 falls, in step 504; and when the first output voltage Vout1 is smaller than the set threshold Vref, the switching tube K is conducted to enable the follow current to supply power to the first output circuit until the follow current is finished or the primary side switch is conducted again. In one embodiment, controlling the switching tube K to be in the off state when the primary switch Q is turned off includes detecting a point of time when the primary switch is turned on by detecting a terminal voltage of the switching tube K, and turning off the switching tube K when the primary switch Q is detected to be turned on. In another embodiment, controlling the switching tube K to be in the off state when the primary side switch Q is turned off includes turning off the switching tube K after a preset time elapses by detecting the turn-on time of the primary side switch Q. Through the control, the first output voltage and the second output voltage can be accurately regulated at the same time, and the problem of cross alignment rate is solved.

Those skilled in the art should understand that the logic controls such as "high" and "low", "set" and "reset", "and gate" and "or gate", "non-inverting input" and "inverting input" in the logic controls referred to in the specification or the drawings may be exchanged or changed, and the subsequent logic controls may be adjusted to achieve the same functions or purposes as the above-mentioned embodiments.

The description and applications of the invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. The descriptions related to the effects or advantages in the specification may not be reflected in practical experimental examples due to uncertainty of specific condition parameters or influence of other factors, and the descriptions related to the effects or advantages are not used for limiting the scope of the invention. Variations and modifications of the embodiments disclosed herein are possible, and alternative and equivalent various components of the embodiments will be apparent to those skilled in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other components, materials, and parts, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.

Claims

1. A flyback multiple output power supply system, comprising:

a primary side circuit comprising a primary side switch;

the transformer comprises a primary winding and a secondary winding, wherein the primary winding is coupled with a primary switch;

the first output circuit comprises a first one-way conduction device and a switching tube which are coupled with the secondary winding and connected in series, and the first output circuit provides a first output voltage at a first output end;

a second output circuit comprising a second unidirectional conducting device coupled to the secondary winding, the second output circuit providing a second output voltage at a second output terminal, wherein the second output voltage is greater than the first output voltage; and

the control circuit is provided with a signal input end and an output end, wherein the signal input end of the control circuit is coupled with the first output end, the output end of the control circuit is coupled with the control end of the switching tube and used for controlling the switching-on and the switching-off of the switching tube, when the primary side switch is switched off, the control circuit controls the switching tube to be in a switching-off state, and when the first output voltage is smaller than a preset threshold value, the control circuit controls the switching-on of the switching tube.

2. The multiple output power supply system of claim 1 wherein the switching tube is controlled to be off during the time that the primary side switch is on.

3. The multi-output power supply system of claim 1 further comprising:

the isolated feedback loop detects the second output voltage to generate a feedback signal; and

and the primary side control circuit is coupled with the primary side switch and controls the primary side switch based on the feedback signal.

4. The multi-output power supply system of claim 3 wherein the control circuit includes a comparison circuit for comparing a sampled signal indicative of the first output voltage with a threshold signal, wherein the switching tube is in an off state when the primary switch is off, and wherein the control circuit turns on the switching tube when the control circuit detects that the sampled signal is less than the threshold signal.

5. The multi-output power supply system of claim 3 wherein the control circuit comprises:

the comparator circuit is provided with a non-inverting input end, an inverting input end and an output end, wherein the non-inverting input end of the comparator circuit receives a threshold signal, and the inverting input end of the comparator circuit is coupled with the first output end;

the window time control circuit is provided with an input end and an output end, and the input end of the window time control circuit is coupled with one end of the switching tube;

the trigger circuit is provided with a set input end, a reset input end and an output end, wherein the set input end is coupled with the output end of the comparison circuit, and the reset input end is coupled with the output end of the window time control circuit; and

and the input end of the driving circuit is coupled with the output end of the trigger circuit, and the output end of the driving circuit is coupled with the control end of the switching tube.

6. The multi-output power supply system according to claim 1, wherein the first unidirectional conducting device comprises a first diode, the second unidirectional conducting device comprises a second diode, an anode terminal of the first diode is coupled to an anode terminal of the second diode and further coupled to a first terminal of the secondary winding, a second terminal of the secondary winding is coupled to a ground reference of the secondary winding, a cathode terminal of the first diode is coupled to a first terminal of the switching tube, a second terminal of the switching tube is coupled to the first output terminal, and a cathode terminal of the second diode is coupled to the second output terminal.

7. The multiplexed output power supply system of claim 1 wherein the secondary winding comprises a first secondary winding and a second secondary winding, wherein the first secondary winding is coupled to the first unidirectional conducting device and the second secondary winding is coupled to the second unidirectional conducting device.

8. The multi-output power supply system of claim 1 wherein the second output voltage is used to power the control circuit.

9. A control circuit for a flyback multiple-output power supply system, wherein the flyback multiple-output power supply system provides a first output voltage at a first output terminal of a secondary side and a second output voltage at a second output terminal, the control circuit has a signal input terminal and an output terminal, wherein the signal input terminal of the control circuit is coupled to the first output terminal for obtaining a sampling signal representing the first output voltage, the output terminal of the control circuit is coupled to a control terminal of a switching tube for controlling the switching-on and switching-off of the switching tube, wherein the switching tube is coupled to the first output terminal, wherein when a primary side switch is turned off, the switching tube is in a turn-off state, and when the first output voltage is less than a preset threshold value, the control circuit controls the switching tube to be turned on, wherein the control circuit comprises:

the comparator circuit is provided with a non-inverting input end, an inverting input end and an output end, wherein the non-inverting input end of the comparator circuit receives the threshold signal, and the inverting input end of the comparator circuit is coupled with the first output end;