Flyback switching power supply circuit and power supply system

Abstract

The utility model relates to a flyback switching power supply circuit and a power supply system, the power supply circuit comprises a rectification circuit, a power switch tube, an auxiliary capacitor, a secondary side circuit, a transformer and a control unit, the transformer comprises a primary winding and a secondary winding which are opposite in polarity, one end of the primary winding is connected with an anode output terminal of the rectification circuit, and the other end of the primary winding is connected with a cathode output terminal of the rectification circuit; the other end of the secondary winding is connected with the cathode output terminal of the rectifying circuit through a power switch tube and an auxiliary capacitor in sequence; and the secondary winding is coupled to a load through a secondary side circuit. An input electrolytic capacitor is cancelled, energy stored in an auxiliary capacitor is used for supplying power to a primary winding through different paths in the turn-on period and the turn-off period of a power switch tube, and stable work of the system is maintained, so that the cost of the power supply circuit and the power supply system is reduced, and the size of the power supply circuit and the power supply system is reduced. And voltage ripples of the power supply circuit and the power supply system are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of switching power supply, in particular to a flyback switching power supply circuit and a power supply system. BACKGROUND

[0002] In the traditional flyback switching power supply design, in order to ensure the stable operation of the system, a high-voltage electrolytic capacitor (EC electrolytic capacitor) is usually used for energy storage after the rectification of the alternating current input. The function of the electrolytic capacitor is to establish a relatively smooth direct current voltage on the rectified pulsating direct current voltage, thereby providing a stable power supply for the subsequent circuit. If there is no EC electrolytic capacitor, after the rectification of the input alternating current voltage, when the input voltage cannot meet the energy of the output, the transformer has no energy transmission to the corresponding winding, resulting in that the output of the flyback switching power supply cannot work normally.

[0003] However, the high-voltage electrolytic capacitor has the problems of large size and high cost due to the factors such as complex material and structure, high voltage resistance requirement, complex manufacturing process, high cost of raw materials, strict performance and reliability requirements, etc. Therefore, the introduction of the high-voltage electrolytic capacitor does not help the miniaturization and cost optimization of the flyback switching power supply. CONTENT OF THE INVENTION

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a flyback switching power supply circuit and a power supply system, which cancels the input electrolytic capacitor in the existing flyback switching power supply circuit, so as to reduce the size and cost of the flyback switching power supply circuit and the power supply system.

[0005] To achieve the above-mentioned purpose and other related purposes, the present application provides a flyback switching power supply circuit, comprising:

[0006] a rectifier circuit, an input terminal of the rectifier circuit being coupled to an alternating current power supply, an output terminal of the rectifier circuit being not coupled to an input electrolytic capacitor;

[0007] a power switch tube;

[0008] an auxiliary capacitor;

[0009] a secondary side circuit;

[0010] a transformer, the transformer comprising a primary winding and a secondary winding with opposite polarities, one end of the primary winding being connected to a positive output terminal of the rectifier circuit, the other end of the primary winding being connected to a negative output terminal of the rectifier circuit through the power switch tube and the auxiliary capacitor in sequence, the secondary winding being coupled to a load through the secondary side circuit; and

[0011] a control unit, the control unit being used for controlling the on-off of the power switch tube;

[0012] Wherein, during the operation of the flyback switching power supply circuit, when the voltage outputted by the rectifier circuit is less than a preset voltage and the power switch tube is in the on state, the energy stored in the auxiliary capacitor flows out from the positive pole of the auxiliary capacitor, and sequentially flows into the negative pole of the auxiliary capacitor through the rectifier circuit, the primary winding and the power switch tube, so as to supply power to the primary winding.

[0013] In an optional embodiment of the present application, the flyback switching power supply circuit further comprises a reverse diode, which is connected reversely between the input end and the output end of the power switch tube.

[0014] After the power switch tube is turned off, when the energy stored in the primary winding cannot meet the energy demand of the output, the energy stored in the auxiliary capacitor is used to supply power to the primary winding reversely through the reverse diode, so that the reflected voltage on the primary winding of the transformer is maintained in the normal working range, and energy is provided for the secondary side circuit.

[0015] In an optional embodiment of the present application, the power switch tube is a MOS tube, and the reverse diode is a body diode or an external diode of the MOS tube.

[0016] In an optional embodiment of the present application, the secondary side circuit comprises an output switching device and an output capacitor.

[0017] The output capacitor is coupled to the load.

[0018] One end of the secondary winding is connected to the first end of the output switching device, and the other end is connected to one end of the output capacitor, and the other end of the output capacitor is connected to the second end of the output switching device.

[0019] In an optional embodiment of the present application, a feedback circuit is further included, one end of the feedback circuit is coupled to the auxiliary capacitor, and the other end is connected to the control unit.

[0020] The feedback circuit is used for monitoring the voltage across the auxiliary capacitor and feeding back to the control unit.

[0021] In an optional embodiment of the present application, the feedback circuit comprises a first feedback resistor and a second feedback resistor.

[0022] One end of the first feedback resistor is connected to the positive pole of the auxiliary capacitor, and the other end is connected to one end of the second feedback resistor and the control unit, respectively, and the other end of the second feedback resistor is connected to the negative pole of the auxiliary capacitor.

[0023] In an optional embodiment of the present application, the voltage across the output capacitor is related to the overload condition of the secondary side circuit.

[0024] In an optional embodiment of the present application, the flyback switching power supply circuit further comprises an auxiliary diode, and the transformer further comprises an auxiliary winding, the polarity of the auxiliary winding being opposite to that of the primary winding.

[0025] The anode of the auxiliary diode is connected to the negative pole of the auxiliary capacitor, the cathode of the auxiliary diode is connected to one end of the auxiliary winding, and the other end of the auxiliary winding is connected to the negative pole output terminal of the rectifier circuit and the positive pole of the auxiliary capacitor, respectively.

[0026] In an optional embodiment of the present application, a current-limiting resistor is further included, which is connected in series between the power switch tube and the auxiliary capacitor.

[0027] To achieve the above object and other related objects, the present application provides a power supply system, which comprises the flyback switching power supply circuit and a load, the load being connected to the output terminal of the flyback switching power supply circuit.

[0028] The flyback switching power supply circuit of the present application comprises a rectifier circuit, a power switch tube, an auxiliary capacitor, a secondary side circuit, a transformer, a reverse diode and a control unit. The transformer comprises a primary winding and a secondary winding, the polarity of the primary winding being opposite to that of the secondary winding. One end of the primary winding is connected to the positive pole output terminal of the rectifier circuit, and the other end is connected to the negative pole output terminal of the rectifier circuit in sequence through the power switch tube and the auxiliary capacitor. The secondary winding is coupled to a load through the secondary side circuit. The reverse diode is connected in reverse between the input and output terminals of the power switch tube. By canceling the input electrolytic capacitor, when the voltage output by the rectifier circuit is less than a preset voltage and the power switch tube is in the on state, the energy stored in the auxiliary capacitor flows out from the positive pole of the auxiliary capacitor and flows into the negative pole of the auxiliary capacitor in sequence through the rectifier circuit, the primary winding and the power switch tube, so as to supply power to the primary winding. When the power switch tube is in the off state, the primary winding transmits the stored energy to the secondary winding, so as to supply power to the secondary side circuit. Meanwhile, after the power switch tube is turned off, when the energy stored in the primary winding cannot meet the energy demand of the output, the energy of the auxiliary capacitor is used to supply power to the primary winding through the reverse diode, so as to maintain the reflected voltage on the primary winding within the normal working range, to provide energy for the secondary side circuit and maintain the stable operation of the system. Thus, the cost of the flyback switching power supply circuit and the power supply system is reduced, the volume of the flyback switching power supply circuit and the power supply system is reduced, and the voltage ripple of the flyback switching power supply circuit and the power supply system is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 a circuit diagram of a flyback switching power supply circuit according to an embodiment of the present application;

[0030] Figure 2 a circuit diagram of a flyback switching power supply circuit according to another embodiment of the present application;

[0031] Figure 3 a circuit diagram of a flyback switching power supply circuit according to another embodiment of the present application; Figure 1 a schematic diagram of a flyback switching power supply circuit according to the present application, in which the voltage after rectification of the input AC voltage meets the energy requirement of the output, and the reflected discharge at the turn-off of the power switch tube;

[0032] Figure 4 a schematic diagram of a flyback switching power supply circuit according to the present application, in which the voltage after rectification of the input AC voltage meets the energy requirement of the output, and the reflected discharge at the turn-off of the power switch tube; Figure 1 a schematic diagram of a flyback switching power supply circuit according to the present application, in which the voltage after rectification of the input AC voltage cannot meet the energy requirement of the output, and the auxiliary capacitor supplies power to the primary winding at the turn-on of the power switch tube;

[0033] Figure 5 a schematic diagram of a flyback switching power supply circuit according to the present application, in which the voltage after rectification of the input AC voltage cannot meet the energy requirement of the output, and the auxiliary capacitor supplies power to the primary winding at the turn-off of the power switch tube through the reverse diode; Figure 1 a schematic diagram of a flyback switching power supply circuit according to the present application, in which the voltage after rectification of the input AC voltage cannot meet the energy requirement of the output, and the auxiliary capacitor supplies power to the primary winding at the turn-off of the power switch tube through the reverse diode;

[0034] Figure 6 a schematic diagram of voltage ripple of a flyback switching power supply circuit according to the present application. DETAILED DESCRIPTION

[0035] The present application is herein described, by way of example only, with the comprehension that the advantages and utility thereof are not limited thereto. It will be clear that from the foregoing description and accompanying drawings, and by variation of or

[0036] Reference will now be made to the following descriptions rendered by way of example in conjunction with the accompanying drawings wherein: Figures 1-6 It is also need to be noted that the drawings used in the following description are provided by way of example only. In the drawings, the size, the relative sizes, and other dimensions of the components shown therein are chosen principally for the purpose of illustrating the application and are not necessarily drawn to scale, and that the shapes, relative sizes, and proportions of the various regions and components shown in the drawings are not necessarily drawn to scale and may have been exaggerated for the purpose of illustration.

[0037] As shown in Figure 1 and 2As shown, the application discloses a flyback switching power supply circuit applied to a power supply system, which comprises a rectifier circuit 10, a power switch tube M1, an auxiliary capacitor Cb, a secondary side circuit, a transformer, a reverse diode and a control unit 20. The flyback switching power supply circuit cancels an input electrolytic capacitor, reduces the cost of the flyback switching power supply circuit, reduces the volume of the flyback switching power supply circuit, and is also helpful to reduce voltage ripple.

[0038] As shown in Figure 1 and 2 in the application, the input terminal of the rectifier circuit 10 is coupled to an alternating current power supply, which can be an alternating current power supply of 85V-264V; the positive output terminal (indicated as "+" in Figure 1 and 2 ) and the negative output terminal (indicated as "-" in Figure 1 and 2 ) of the rectifier circuit 10 are not coupled to an input electrolytic capacitor. The rectifier circuit 10 is used for rectifying the alternating voltage input by the input terminal and delivering the rectified alternating voltage to the primary winding Np of the transformer.

[0039] As shown in Figure 1 and 2 in the application, the rectifier circuit 10 adopts a bridge rectifier circuit, which is composed of four diodes and arranged in a bridge structure in the circuit, so as to realize full-wave rectification. It can be understood that in other embodiments, the diodes in the bridge rectifier circuit can also be replaced by NMOS tubes, PMOS tubes, transistors and other switch tubes. It can be understood that in other embodiments, the rectifier circuit 10 can also adopt a full-wave rectifier circuit.

[0040] As shown in Figure 1 and 2 in the application, the flyback switching power supply circuit further comprises an auxiliary diode Db. The transformer realizes voltage conversion and electrical isolation by storing and releasing energy, which comprises a primary winding Np, a secondary winding Ns and an auxiliary winding Nb. One end of the primary winding Np is connected with the positive output terminal of the rectifier circuit 10, and the other end is sequentially connected with the negative output terminal of the rectifier circuit 10 through the power switch tube M1 and the auxiliary capacitor Cb; the secondary winding Ns is coupled to a load through the secondary side circuit; one end of the auxiliary winding Nb is connected with the cathode of the auxiliary diode Db, and the other end of the auxiliary winding Nb is connected with the negative output terminal of the rectifier circuit 10 and the positive electrode of the auxiliary capacitor Cb respectively; the anode of the auxiliary diode Db is connected with the negative electrode of the auxiliary capacitor Cb. The load can be a direct current motor or a direct current water pump and the like.

[0041] Specifically, the auxiliary capacitor Cb is an electrolytic capacitor, the opposite end of the primary winding Np is connected with the positive output terminal of the rectifier circuit 10, the same end of the primary winding Np is connected with the input end of the power switch tube M1, the output end of the power switch tube M1 is connected with the negative pole of the auxiliary capacitor Cb and the anode of the auxiliary diode Db through the current-limiting resistor Rcs respectively, the cathode of the auxiliary diode Db is connected with the opposite end of the auxiliary winding Nb, and the same end of the auxiliary winding Nb is connected with the positive pole of the auxiliary capacitor Cb and the negative output terminal of the rectifier circuit 10. It should be noted that the capacity of the auxiliary capacitor Cb is positively correlated with the current flowing through the power switch tube M1, that is, the greater the maximum current flowing through the power switch tube M1, the greater the capacitance of the auxiliary capacitor Cb.

[0042] It should be noted that in order to realize flyback power supply, the primary winding Np needs to store electric energy when the power switch tube M1 is turned on, and the primary winding Np releases energy to the secondary winding Ns to supply power to the load and the output capacitor Co, and releases energy to the auxiliary winding Nb to charge the auxiliary capacitor Cb when the power switch tube M1 is turned off. The same end of the primary winding Np is arranged opposite to the same end of the secondary winding Ns, and the same end of the secondary winding Ns and the same end of the auxiliary winding Nb are arranged in the same way, so as to ensure that the polarity of the primary winding Np is opposite to the polarity of the secondary winding Ns and the polarity of the auxiliary winding Nb, and the polarity of the secondary winding Ns and the polarity of the auxiliary winding Nb are the same.

[0043] As shown in Figure 1 and 2 In the present application, the power switch tube M1 can adopt NMOS tube, PMOS tube, triode and the like. The anode of the auxiliary diode Db is coupled with the negative pole of the auxiliary capacitor Cb. Specifically, the anode of the auxiliary diode Db is coupled with the negative pole of the auxiliary capacitor Cb.

[0044] As shown in Figure 1 and 2 In a specific embodiment, the power switch tube M1 is an NMOS tube with a body diode, the drain D of the NMOS tube is the input end, the source S is the output end, and the gate G is the control end. The body diode or an independent diode connected externally can be used as the reverse diode.

[0045] In another specific embodiment, the power switch tube M1 is a PMOS tube with a body diode, the source of the NMOS tube is the input end, the drain is the output end, and a body diode or an externally connected independent diode can also be used as the reverse diode.

[0046] As shown in Figure 1 and 2 In the present application, the secondary side circuit includes an output switching device, such as a diode Ds or a synchronous rectifier, and an output capacitor Co; the output capacitor Co is coupled to the load; one end of the secondary winding Ns is connected to a first end of the output switching device, the other end is connected to one end of the output capacitor Co, the other end of the output capacitor Co is connected to a second end of the output switching device; the output switching device can be in a cut-off state when the power switch tube M1 is turned on, and the output capacitor Co supplies power to the load, and in a conductive state when the power switch tube M1 is turned off, and the energy released from the primary winding Np to the secondary winding Ns supplies power to the output capacitor Co and the load.

[0047] As shown in Figure 2 In the present application, the flyback switching power supply circuit further includes a feedback circuit 30, one end of the feedback circuit 30 is coupled to the auxiliary capacitor Cb, and the other end is connected to the control unit 20; the feedback circuit 30 is used to monitor the voltage across the auxiliary capacitor Cb and feedback to the control unit 20; the control unit 20 can realize the adjustment control of the flyback switching power supply circuit according to the feedback voltage Vfb.

[0048] In the present application, the feedback circuit 30 adopts a voltage dividing circuit design, including a first feedback resistor Rfb1 and a second feedback resistor Rfb2; one end of the first feedback resistor Rfb1 is connected to the positive electrode of the auxiliary capacitor Cb, and the other end is connected to one end of the second feedback resistor Rfb2 and the control unit 20, respectively; the other end of the second feedback resistor Rfb2 is connected to the negative electrode of the auxiliary capacitor Cb.

[0049] It should be noted that, since the auxiliary capacitor Cb is connected in series in the charging path of the primary winding Np, during the conduction of the power switch tube Ml, the current flowing from the negative electrode to the positive electrode of the auxiliary capacitor Cb, the energy stored in the auxiliary capacitor Cb is discharged, and when the power switch tube Ml is turned off, the auxiliary winding Nb uses the energy released in the primary winding Np to charge the auxiliary capacitor Cb, so that the energy stored in the auxiliary capacitor Cb during the power switch tube Ml is turned off. The energy stored in the primary winding Np is positively correlated, and the voltage of the auxiliary capacitor Cb can reflect the output voltage of the flyback switching power supply circuit, that is, the terminal voltage of the output capacitor Co. The output voltage of the flyback switching power supply circuit can be monitored by monitoring the terminal voltage of the auxiliary capacitor Cb, and the dynamic response of the flyback switching power supply circuit is improved.

[0050] As shown in Figure 1 and 2 The control unit 20 is connected with the control end of the power switch tube Ml, and the control unit 20 is used to control the on-off of the power switch tube Ml to control the flyback switching power supply to supply energy for the load.

[0051] The working mechanism of the flyback switching power supply circuit of the present application will be described in detail below in conjunction with the accompanying Figures 3-5

[0052] As shown in Figure 3 ​As shown, when the voltage after rectification by the rectifier circuit 10 of the input AC power supply can meet the output energy demand, when the power switch M1 is turned on, energy flows out from the positive output terminal of the rectifier circuit 10, passes sequentially through the primary winding Np, the power switch M1, the current limiting resistor Rcs, and the auxiliary capacitor Cb, and then flows into the negative output terminal of the rectifier circuit 10. The primary winding Np stores energy, and at the same time, the energy stored in the auxiliary capacitor Cb is also released during this process, which prepares for the subsequent detection of the output voltage of the flyback switching power supply circuit by the auxiliary capacitor Cb, thereby improving the dynamic response. Because the secondary winding Ns and the primary winding Np have opposite polarities, the output diode Ds is in the off state, the secondary winding Ns does not release energy, and the load is powered by the output capacitor Co. At this time, the auxiliary winding Nb and the primary winding Np have opposite polarities, the auxiliary diode Ds is in the off state, and the auxiliary winding Nb cannot charge the auxiliary capacitor Cb. When the power switch M1 is turned off, the reflected voltage of the primary winding Np will be induced in the secondary winding Ns and the auxiliary winding Nb. When the output voltage is opposite to that when the power switch M1 is turned on, the output diode Ds and the auxiliary diode Db turn on, and the energy stored in the primary winding Np is released to the secondary winding Ns and the auxiliary winding Nb. This creates current in the secondary circuit, part of which charges the output capacitor Co to maintain a stable output voltage, and the other part supplies power to the load in the subsequent stage. Simultaneously, current also flows in the circuit of the auxiliary winding Nb, the auxiliary diode Db, and the auxiliary capacitor Cb, which can charge the auxiliary capacitor Cb.

[0053] like Figure 4 As shown, when the voltage after rectification by the rectifier circuit 10 cannot meet the output energy demand, or when the voltage across the positive and negative output terminals of the rectifier circuit 10 is 0V or within a preset range of 0V (corresponding to an AC input voltage angle of 0° or 180°), when the power switch M1 is turned on, the energy stored in the auxiliary capacitor Cb flows along... Figure 4from the positive pole of the auxiliary capacitor Cb, and sequentially flows into the negative pole of the auxiliary capacitor Cb through the rectifier circuit 10, the primary winding Np, the power switch tube Ml and the current-limiting resistor Rcs, to supplement the energy of the primary winding Np. If the energy stored in the primary winding Np after the energy supplement can meet the energy demand of the output, the primary winding Np will transfer the stored energy to the secondary winding Ns and the auxiliary winding Nb when the power switch tube Ml is turned off, the secondary winding Ns uses the energy transferred from the primary winding Np to supply power to the output capacitor Co and the load in the subsequent stage, and the auxiliary winding Nb uses the energy transferred from the primary winding Np to charge the auxiliary capacitor Cb. If the energy stored in the primary winding Np after the energy supplement still cannot meet the energy demand of the output, the energy of the auxiliary capacitor Cb will flow along the red dashed line path in Figure 5 Figure 5 to supplement the energy of the primary winding Np of the transformer in reverse direction through the reverse diode, so as to maintain the reflected voltage on the primary winding Np of the transformer in the normal working range, to provide energy for the secondary side circuit and maintain the stable working of the system. It should be noted that the voltage after the rectification of the input alternating voltage by the rectifier circuit 10 cannot meet the energy demand of the output, or the voltage between the positive and negative output terminals of the rectifier circuit 10 is 0V or in the preset range (corresponding to the angle of the alternating input voltage near 0° or 180°) near 0V, at this time, the voltage output by the rectifier circuit 10 is less than the preset voltage, and since the auxiliary capacitor Cb can supply power to the primary winding Np during the conduction and turn-off of the power switch tube Ml, the voltage between the output capacitor Cb can maintain the output voltage of the flyback switching power supply circuit constant. By canceling the input electrolytic capacitor after rectification, the volume and cost of the flyback switching power supply circuit are reduced, and the output voltage ripple is also reduced.

[0054] As shown in Figure 6 , the flyback switching power supply circuit of the present application also helps to reduce the voltage ripple, and in the case of an output voltage of 24V, the peak value of the ripple voltage is 660mV, and the voltage ripple rate is about 2.75%.

[0055] As shown in Figure 1 and 2 , the present application discloses a power supply system, which comprises the flyback switching power supply circuit and a load (not shown in the figure), and the load is connected to the output end of the flyback switching power supply circuit.

[0056] ​The flyback switching power supply circuit of the application comprises a rectifier circuit 10, a power switch tube M1, an auxiliary capacitor Cb, a secondary side circuit, a transformer, a reverse diode and a control unit 20, the transformer comprises a primary winding Np and a secondary winding Ns with opposite polarities, one end of the primary winding Np is connected with a positive output terminal of the rectifier circuit 10, the other end is connected with a negative output terminal of the rectifier circuit 10 in turn through the power switch tube M1, the auxiliary capacitor Cb and the secondary side circuit is coupled to a load; the reverse diode is connected reversely between the input and output terminals of the power switch tube M1. By canceling the input electrolytic capacitor, when the voltage output by the rectifier circuit 10 is less than the preset voltage and the power switch tube M1 is in the on state, the energy stored in the auxiliary capacitor Cb flows out from the positive electrode of the auxiliary capacitor Cb and flows into the negative electrode of the auxiliary capacitor Cb in turn through the rectifier circuit 10, the primary winding Np and the power switch tube M1, so as to supply power for the primary winding Np; when the power switch tube M1 is in the off state, the primary winding Np transmits the stored energy to the secondary winding Ns to supply power for the secondary side circuit; at the same time, after the power switch tube M1 is turned off, when the energy stored in the primary winding Np still cannot meet the energy demand of the output, the energy of the auxiliary capacitor Cb is used to supply power for the primary winding Np through the reverse diode, so that the reflected voltage on the primary winding Np is maintained in the normal working range, the energy is provided for the secondary side circuit, the stable working of the system is maintained, and the cost of the flyback switching power supply circuit and the power supply system is reduced, the volume of the flyback switching power supply circuit and the power supply system is reduced, and the output voltage ripple of the flyback switching power supply circuit and the power supply system is reduced. Therefore, the application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0057] The above description of the embodiments shown in the application (including the content in the abstract) is not intended to be exhaustive or to limit the application to the precise form disclosed herein. Although specific embodiments of the application and examples of the application are described herein for illustrative purposes, various equivalent modifications are possible within the spirit and scope of the application, as will be recognized and appreciated by those skilled in the art. As indicated, these modifications can be made to the application in light of the above description of the embodiments of the application, and the modifications will be within the spirit and scope of the application.

[0058] The systems and methods have been described herein in general terms as helpful to understand the details of the application. Moreover, various specific details have been given in order to provide a thorough understanding of embodiments of the application. However, one skilled in the relevant art will recognize that embodiments of the application can be practiced without one or more of the specific details, or with other apparatuses, systems, assemblies, methods, components, materials, parts, and the like. In other instances, well known structures, materials, and / or operations have not been shown or described in detail in order to avoid obscuring aspects of embodiments of the application.

[0059] Thus, although the application has been described herein with reference to particular embodiments thereof, changes in the form and details of the various steps can be made to adapt the application to various environments, and / or materials, without departing from the spirit of the application. Therefore, many modifications can be made to carry out the application in its broader aspects, without departing from its scope and spirit. The application is thus not limited to the specific embodiments described herein, but only by the claims that follow, the intent being that equivalents be covered and that obvious modifications be contemplated. The scope of the application, therefore, is to be determined solely by the following claims.

Claims

1. A flyback switching power supply circuit, characterized in that, include: A rectifier circuit, wherein the input terminals of the rectifier circuit are coupled to an AC power supply, and the output terminals of the rectifier circuit are not coupled to an input electrolytic capacitor; Power switching transistors; Auxiliary capacitor; Secondary side circuit; A transformer, comprising a primary winding and a secondary winding of opposite polarity, wherein one end of the primary winding is connected to the positive output terminal of the rectifier circuit, and the other end is connected to the negative output terminal of the rectifier circuit in sequence through a power switch and an auxiliary capacitor; the secondary winding is coupled to a load through a secondary-side circuit; and A control unit, which is used to control the on / off state of the power switching transistor; During the operation of the flyback switching power supply circuit, when the voltage output by the rectifier circuit is less than the preset voltage and the power switch is in the on state, the energy stored in the auxiliary capacitor flows out from the positive terminal of the auxiliary capacitor and flows sequentially through the rectifier circuit, the primary winding, and the power switch to the negative terminal of the auxiliary capacitor to supply power to the primary winding.

2. The flyback switching power supply circuit according to claim 1, characterized in that, The flyback switching power supply circuit also includes a reverse diode, which is connected in reverse parallel between the input and output terminals of the power switching transistor. When the power switch is turned off and the energy stored in the primary winding is insufficient to meet the output energy demand, the energy stored in the auxiliary capacitor is used to supply power to the primary winding in reverse through the reverse diode, so that the reflected voltage on the primary winding of the transformer is maintained within the normal operating range, thus providing energy to the secondary circuit.

3. The flyback switching power supply circuit according to claim 2, characterized in that, The power switch is a MOSFET, and the reverse diode is either the body diode of the MOSFET or an external diode.

4. The flyback switching power supply circuit according to claim 1, characterized in that, The secondary circuit includes an output switching device and an output capacitor; The output capacitor is coupled to the load; One end of the secondary winding is connected to the first end of the output switching device, and the other end is connected to one end of the output capacitor. The other end of the output capacitor is connected to the second end of the output switching device.

5. The flyback switching power supply circuit according to claim 1, characterized in that, It also includes a feedback circuit, one end of which is coupled to the auxiliary capacitor and the other end is connected to the control unit; The feedback circuit is used to monitor the voltage across the auxiliary capacitor and feed it back to the control unit.

6. The flyback switching power supply circuit according to claim 5, characterized in that, The feedback circuit includes a first feedback resistor and a second feedback resistor; One end of the first feedback resistor is connected to the positive terminal of the auxiliary capacitor, and the other end is connected to one end of the second feedback resistor and the control unit, respectively. The other end of the second feedback resistor is connected to the negative terminal of the auxiliary capacitor.

7. The flyback switching power supply circuit according to claim 4, characterized in that, The voltage across the output capacitor reflects the overload condition of the secondary circuit.

8. The flyback switching power supply circuit according to claim 1, characterized in that, The flyback switching power supply circuit also includes an auxiliary diode, and the transformer also includes an auxiliary winding, the polarity of which is opposite to that of the primary winding; The anode of the auxiliary diode is connected to the cathode of the auxiliary capacitor, the cathode of the auxiliary diode is connected to one end of the auxiliary winding, and the other end of the auxiliary winding is connected to the negative output terminal of the rectifier circuit and the positive terminal of the auxiliary capacitor.

9. The flyback switching power supply circuit according to claim 1, characterized in that, It also includes a current-limiting resistor, which is connected in series between the power switch and the auxiliary capacitor.

10. A power supply system, characterized in that, include: The flyback switching power supply circuit and load as described in any one of claims 1-9, wherein the load is connected to the output terminal of the flyback switching power supply circuit.

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