Flyback converter

Abstract

The invention discloses a flyback converter. The flyback converter comprises an input circuit, a primary side control and power conversion circuit and an output circuit, and the input circuit is used for converting alternating current voltage into direct current voltage; the primary side control and power conversion circuit is used for performing power conversion on the direct-current voltage; the output circuit is used for sensing to obtain the voltage after power conversion and outputting the voltage; wherein the primary side control and power conversion circuit comprises a first primary side main winding, a power switch and a second primary side main winding; when the power switch is closed, the first primary side main winding and the second primary side main winding are connected in series through the power switch. By adopting the scheme, the electromagnetic interference of the flyback converter can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of switching power supplies, and in particular to a flyback converter. Background Art

[0002] Flyback converters are widely used in AC / DC and DC / DC conversion, and provide insulation isolation between the input and output stages. They are a type of switching power supply and are widely used in various consumer electronic products. High efficiency and low noise solutions are extremely important for reducing system costs and improving user experience.

[0003] However, there are certain electromagnetic interference (EMI) problems in the topology of the existing flyback converter. Summary of the invention

[0004] The problem to be solved by the present invention is: how to reduce the electromagnetic interference of a flyback converter.

[0005] To solve the above problems, an embodiment of the present invention provides a flyback converter, the flyback converter comprising: an input circuit, a primary side control and power conversion circuit, and an output circuit, wherein: The input circuit is used to convert AC voltage into DC voltage; The primary side control and power conversion circuit is used to perform power conversion on the DC voltage; The output circuit is used to sense and output the voltage after power conversion; Wherein, the primary control and power conversion circuit includes: a first primary main winding, a power switch and a second primary main winding; when the power switch is closed, the first primary main winding and the second primary main winding are connected in series through the power switch.

[0006] In a possible embodiment, the same-name end of the first primary main winding is connected to one end of the power switch, and the opposite-name end of the second primary main winding is directly or indirectly connected to the other end of the power switch.

[0007] In a possible embodiment, the output circuit includes: an output winding; the first primary main winding, the second primary main winding, and the output winding are wound layer by layer on the same magnetic core to form a transformer.

[0008] In a possible embodiment, the ratio of the number of turns of the first primary main winding to that of the second primary main winding is used to balance the common mode current of the transformer.

[0009] In a possible embodiment, the primary control and power conversion circuit further includes: a primary controller; the second primary main winding is connected to the power supply end of the primary controller to supply power to the primary controller.

[0010] In a possible embodiment, the primary control and power conversion circuit also includes: a rectifier circuit and an energy storage subcircuit; the rectifier circuit is used to rectify the voltage provided by the second primary main winding, and the energy storage subcircuit is used to store the voltage rectified by the rectifier circuit and provide it to the power supply end of the primary controller.

[0011] In a possible embodiment, the rectifier circuit includes: a rectifier diode; or a rectifier diode and a fifth resistor connected in series.

[0012] In a possible embodiment, the energy storage subcircuit includes: a first capacitor; or a first capacitor and a second capacitor connected in parallel.

[0013] In a possible embodiment, the primary side control and power conversion circuit further includes: a starting resistor; one end of the starting resistor is connected to the input circuit, and the other end is connected to the first capacitor and the second capacitor.

[0014] In a possible embodiment, the primary control and power conversion circuit also includes: a primary controller; the second primary main winding is also connected to the control signal end of the primary controller, for providing a control signal to the primary controller so that the primary controller can perform control operations.

[0015] In a possible embodiment, the primary control and power conversion circuit also includes: a third resistor and a fourth resistor, the control signal end of the primary controller is connected to the same-name end of the second primary main winding through the third resistor, and the control signal end of the primary controller is connected to the opposite-name end of the second primary main winding through the fourth resistor.

[0016] In a possible embodiment, the primary control and power conversion circuit further includes: a current collection subcircuit, one end of which is connected to the power switch tube, and the other end of which is connected to the second primary main winding.

[0017] In a possible embodiment, the primary control and power conversion circuit further includes: a feedback subcircuit, one end of which is connected to the second primary main winding and the other end is connected to the primary controller, for monitoring the output voltage of the flyback converter.

[0018] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages: By applying the solution of the present invention, when the power switch is closed, since the first primary main winding and the second primary main winding are connected in series through the power switch, the second primary main winding can share the primary voltage of the transformer. Compared with only setting one primary winding, the noise source of the transformer main winding can be decomposed into two parts, including the noise generated by the first primary main winding and the noise generated by the second primary main winding. After the decomposition, the voltage change of each noise source is reduced, thereby reducing electromagnetic interference caused by excessive voltage change.

[0019] Furthermore, the same-name end of the first primary main winding is connected to one end of the power switch, and the opposite-name end of the second primary main winding is connected to the other end of the power switch. Therefore, when the power switch is closed, the voltage at the same-name end of the first primary main winding decreases, but the voltage at the opposite-name end of the second primary main winding increases, thereby making the direction of the common-mode current generated by the second primary main winding opposite to the direction of the common-mode current generated by the first primary main winding, which is beneficial to the balance of the common-mode current inside the transformer, and is also beneficial to solving the EMI problem caused by the imbalance of the common-mode current. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a topological structure diagram of a flyback converter in the prior art; Figure 2 It is a schematic diagram of the internal structure of a transformer in the prior art; Figure 3 It is a schematic diagram of the change of the direction of the common mode current inside a transformer in the prior art; Figure 4 is a topological structure diagram of a flyback converter in an embodiment of the present invention; Figure 5 yes Figure 4 A schematic diagram of voltage variation curves of the first primary main winding and the second primary main winding; Figure 6 is a schematic diagram of the internal structure of a transformer in an embodiment of the present invention; Figure 7 is a schematic diagram of the change of the direction of the common mode current inside a transformer in an embodiment of the present invention; Figure 8 It is a schematic diagram of the winding of each winding inside a transformer; Fig. 9 is a schematic diagram of winding of each winding inside a transformer in an embodiment of the present invention; Fig.10 is a topological structure diagram of another flyback converter in an embodiment of the present invention; Fig.11 is a topological structure diagram of another flyback converter in an embodiment of the present invention; Fig.12is a topological structure diagram of another flyback converter according to an embodiment of the present invention; Fig.13 4 is a topological structure diagram of another flyback converter in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] Figure 1 It is a topology of an existing flyback converter. Figure 1 , the flyback converter may include: an input circuit 11, a primary side control and power conversion circuit 12 and an output circuit 13. Wherein: The input circuit 11 includes: a primary rectifier 111 and a filter subcircuit 112. After the AC voltage is rectified by the primary rectifier 111, it is filtered by the filter subcircuit 112 composed of a first electrolytic capacitor and an inductor to obtain a DC voltage, and the obtained DC voltage is provided to the primary control and power conversion circuit 12.

[0022] The primary control and power conversion circuit 12 includes: a primary main winding Np of a transformer connected in series, an auxiliary winding Na of a transformer, a primary controller and a power switch, etc. Among them, the primary controller and the power switch can be integrated in the power conversion chip U1, and the power switch is located between the switch pin (SW) and the ground pin (GND). One side of the auxiliary winding Na of the transformer also has an auxiliary rectifier D1 and a second electrolytic capacitor C1, and the auxiliary rectifier D1 is located at the positive end of the second electrolytic capacitor C1. The DC voltage provided by the input circuit 11 is input to the power conversion chip U1 through the primary main winding Np of the transformer, and the primary controller can control the on and off of the power switch to achieve power conversion.

[0023] In the output circuit 13, the secondary rectifier 131 is located at the negative end of the output capacitor. The energy of the transformer is transferred to the output winding Ns in a magnetic field induction manner, and a stable DC output is achieved through the secondary rectifier and the output capacitor.

[0024] In the flyback converter of the above topology, refer to Figure 3 When the primary controller controls the power switch to conduct, the switch pin of the power conversion chip U1 (that is, the connection end between the power switch and the primary main winding Np of the transformer) will be short-circuited to the ground. At this time, taking the common-mode current flowing into the output winding Ns as a positive current, the voltage V_Np at the same-name end of the primary main winding Np of the transformer and the voltage V_Na at the same-name end of the auxiliary winding Na of the transformer will become low, thereby generating a negative common-mode current. The voltage V_Ns at the opposite-name end of the output winding Ns will become high, also generating a negative common-mode current.

[0025] In order to balance the negative common-mode current, the transformer must generate a positive common-mode current to offset the negative common-mode current. Therefore, a shielded winding needs to be added to generate a positive common-mode current to avoid electromagnetic interference caused by unbalanced common-mode current.

[0026] Specifically, refer to Figure 2 , inside the transformer, a shield winding is added between the primary main winding Np and the output winding Ns to achieve common mode current balance. When the primary side is turned on, the voltage V_Nss at the same end of the shield winding will decrease and generate a positive common mode current (such as Figure 3 At this time, the positive common-mode current generated by the shield winding will be balanced with the negative common-mode current generated by the primary main winding Np, the auxiliary winding Na and the output winding Ns.

[0027] However, due to the addition of shielded windings inside the transformer, the primary main winding Np and the output winding Ns cannot fit closely together, thus affecting the coupling performance between the primary main winding Np and the output winding Ns, causing large transformer leakage inductance, and even affecting the transformer's voltage conversion efficiency and temperature. In addition, whether sandwich or forward winding is used, the transformer has a certain impact. Moreover, due to the addition of shielded windings inside the transformer, the number of layers inside the transformer increases, resulting in complex processes and increased transformer costs.

[0028] In addition, for a flyback converter using the above topology, even if a shielded winding has been added inside the transformer, when the power switch is disconnected, the voltage at the switch pin (UI-SW) of the power converter U1 will change from zero to (Vin_dc+nVo). Among them, Vin_dc is the DC voltage provided by the input circuit, n is the turns ratio of the transformer, Vo is the output voltage of the transformer, and nVo represents the voltage drop across the transformer. (Vin_dc+nVo) is the main noise source, which makes the voltage at the switch pin (UI-SW) of the power converter U1 change rate with time (dv / dt) larger, so EMI problems will still occur.

[0029] To address this problem, the present invention provides a flyback converter. In the flyback converter, when the power switch is closed, the first primary main winding and the second primary main winding are connected in series through the power switch, so that the noise source of the transformer main winding can be decomposed into two parts, namely the first primary main winding and the second primary main winding. After the decomposition, the voltage change of each noise is reduced, thereby reducing electromagnetic interference caused by excessive voltage change.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] An embodiment of the present invention provides a flyback converter, which may include: an input circuit, a primary side control and power conversion circuit, and an output circuit. The input circuit is used to convert AC voltage into DC voltage; The primary side control and power conversion circuit is used to perform power conversion on the DC voltage; The output circuit is used to sense and output the voltage after power conversion; Wherein, the primary control and power conversion circuit includes: a first primary main winding, a power switch and a second primary main winding; when the power switch is closed, the first primary main winding and the second primary main winding are connected in series through the power switch.

[0032] By adopting the above-mentioned flyback converter, when the power switch is closed, the first primary main winding and the second primary main winding are connected in series through the power switch, thereby making it possible to decompose the noise source of the transformer main winding into two parts, namely, the noise generated by the first primary main winding and the noise generated by the second primary main winding. In this way, the voltage variation of each noise source is reduced, thereby reducing the EMI problem caused by excessive voltage variation.

[0033] In a specific implementation, the primary side control and power conversion circuit may include: a primary side controller and a power switch. The primary side controller and the power switch may be independently configured (e.g. Figure 4 As shown), it can also be integrated in the same power conversion chip (such as Figures 10 to 13 as shown).

[0034] The flyback converter in the embodiment of the present invention is described in detail below in conjunction with a specific circuit structure.

[0035] Figure 4 FIG. 4 is a schematic diagram of a topological structure of a flyback converter 40 according to an embodiment of the present invention. Figure 4 The flyback converter 40 may include: an input circuit 41 , a primary side control and power conversion circuit 42 , and an output circuit 43 .

[0036] The input circuit 41 may include: a primary rectifier 411 and a filter subcircuit 412. The primary rectifier 411 may be implemented by a rectifier bridge. The filter subcircuit 412 may include an electrolytic capacitor and an inductor. After the AC voltage is rectified by the primary rectifier 411, it is filtered by the filter subcircuit 412 to obtain a DC voltage Vin_dc.

[0037] The output circuit 43 may include: an output winding Ns, a secondary rectifier and an output capacitor, wherein the voltage induced by the output winding Ns is rectified by the secondary rectifier and then outputted through the output capacitor.

[0038] In a specific implementation, the primary control and power conversion circuit 42 may include: a first primary main winding Np1, a power switch Q1, and a second primary main winding Np2. When the power switch Q1 is closed, the first primary main winding Np1 is connected in series with the second primary main winding Np2 through the power switch Q1. The second primary main winding Np2 and the first primary main winding Np1 form the main winding of the transformer T1. The second primary main winding Np2 and the first primary main winding Np1 jointly assume the transformer energy storage function, so that the current density in the transformer is more balanced and the utilization rate of the transformer is higher.

[0039] The primary control and power conversion circuit 42 may also include: a primary controller U11. The primary controller U11 also has a gate terminal Gate and a ground terminal GND. The gate terminal Gate is connected to the gate of the power switch Q1 to control the on and off of the power switch Q1. The ground terminal GND is connected to one end B of the second primary main winding Np2. When the power switch Q1 is closed, the voltage at the B end of the second primary main winding Np2 will change, so the B end of the second primary main winding Np2 is a dynamic node, thereby dividing the main winding noise source of the flyback converter into two parts, namely the noise generated by the first primary main winding Np1 and the noise generated by the second primary main winding Np2.

[0040] Among them, refer to Figure 5 , when the power switch Q1 is disconnected, the voltage at the same-name terminal A of the first primary main winding Np1 changes from zero to (n1Vo+Vin_dc), and the voltage at the connection terminal B of the second primary main winding Np2 and the power switch Q1 changes from zero to V1. Where n1 is the ratio of the number of turns of the first primary main winding Np1 to the number of turns of the output winding Ns. Since the number of turns of the first primary main winding Np1 is less than Figure 1 The number of turns of the primary main winding Np is n1<n, so the voltage change at the same end A of the first primary main winding Np1 is less than Figure 1 Therefore, the voltage variation of the first primary main winding Np1 is reduced when the power switch Q1 is turned off, thereby greatly reducing the electromagnetic interference generated by the first primary main winding Np1.

[0041] Therefore, by connecting the first primary main winding Np1 and the second primary main winding Np2 in series, electromagnetic interference caused by excessive voltage variation at the connection terminal between the primary main winding and the primary controller U11 can be greatly reduced.

[0042] In one embodiment of the present invention, in order to avoid electromagnetic interference caused by unbalanced common mode current inside the transformer T1, referring to Figure 4, the same-name end A of the first primary main winding Np1 can be connected to one end of the power switch Q1, and the opposite-name end B of the second primary main winding Np2 can be directly connected to the other end of the power switch Q1.

[0043] At this time, the like-name end A of the first primary main winding Np1 and the opposite-name end B of the second primary main winding Np2 are out-of-phase points, so that the direction of the common-mode current generated by the first primary main winding Np1 can be opposite to the direction of the common-mode current generated by the second primary main winding Np2, and the direction of the noise generated by the first primary main winding Np1 can be opposite to the direction of the noise generated by the second primary main winding Np2, thereby balancing the common-mode current inside the transformer T1 and reducing electromagnetic interference problems.

[0044] Since the common-mode current generated by the second primary main winding Np2 is in opposite direction to the common-mode current generated by the first primary main winding Np1, in one embodiment, the first primary main winding Np1, the second primary main winding Np2 and the output winding Ns are wound layer by layer on the same magnetic core to form a transformer T1.

[0045] Specifically, refer to Figure 6 , a layer of copper wire can be firstly wound on the magnetic core as the first primary main winding Np1. Then, copper wire is wound on top of the copper wire layer of the first primary main winding Np1 to form the second primary main winding Np2. Finally, copper wire is wound on top of the copper wire layer of the second primary main winding Np2 to form the output winding Ns. Among them, the first primary main winding Np1 is fitted with the second primary main winding Np2, and the second primary main winding Np2 is fitted with the output winding Ns. The shielding layer is no longer set inside the transformer T1, and the second primary main winding Np2 provides the reverse common mode current.

[0046] The common mode current flowing into the output winding Ns is the positive common mode current. Figure 7 , when the power switch Q1 is closed, the voltage V_Np1 at the same-name end A of the first primary main winding Np1 will decrease, thereby generating a negative common-mode current. The voltage V_Np2 at the opposite-name end of the second primary main winding Np2 will increase, thereby generating a positive common-mode current. The voltage V_Ns at the opposite-name end of the output winding Ns will increase, also generating a negative common-mode current. In this way, it is more conducive to achieving a balance in the common-mode current inside the transformer T1.

[0047] In one embodiment of the present invention, the ratio of the number of turns of the first primary main winding Np1 to the second primary main winding Np2 can be adjusted to balance the common mode current of the transformer T1. At this time, by adjusting the number of turns of the second primary main winding Np2, the magnitude of the positive common mode current generated inside the transformer T1 can be changed, and by adjusting the number of turns of the first primary main winding Np1, the magnitude of the negative common mode current generated inside the transformer T1 can be changed, and finally the positive common mode current value generated inside the transformer T1 is equal to the negative common mode current value generated inside the transformer T1, so that the common mode currents cancel each other out.

[0048] In one embodiment of the present invention, the sum of the number of turns of the first primary main winding and the number of turns of the second primary main winding can be set equal to the number of turns of the primary main winding before the improvement. In this way, the number of copper wire layers inside the transformer can be reduced without increasing the cost of the primary main winding of the transformer, that is, the shielding layer can be reduced, which can make the coupling between the windings inside the transformer better, thereby improving the conversion efficiency of the transformer and thus improving the output efficiency of the transformer.

[0049] For example, Figure 8 This is a schematic diagram of the internal structure of the transformer before improvement. Figure 8 In the transformer before the improvement, 0.23mm polyurethane enameled wire (2UEW) can be used to start from the 7th foot (7 (s)) of the magnetic core, and 2 layers can be wound clockwise, and then wound out from the 4th foot (4 (s)) of the magnetic core, and each layer can be wound 23 turns (Ts) to form the primary main winding Np. Then the total number of turns of the primary main winding Np is 46 turns. After forming the primary main winding Np, polyurethane enameled wire is used to start from the 6th foot of the magnetic core, and 1 layer is wound clockwise, and then wound out from the 5th foot to form the auxiliary winding Na. The number of turns of the auxiliary winding Na is 10. After the auxiliary winding Na is formed, a shielding layer and an output winding Ns are formed on the auxiliary winding Na. Among them, the number of turns of the shielding layer is 10, and the number of turns of the output winding Ns is 5.

[0050] Fig. 9 Schematic diagram of the internal structure of the transformer in the embodiment of the present invention. Fig. 9, 0.29mm polyurethane enameled wire (2UEW) is used to start from the 7th foot (7 (s)) of the magnetic core, and 2 layers are wound clockwise, and then wound out from the 4th foot (4 (s)) of the magnetic core, and each layer is wound 18 turns to form the first primary main winding Np1, then the total number of turns of the first primary main winding Np1 is 36 turns. After forming the first primary main winding Np1, polyurethane enameled wire is used to start from the 5th foot of the magnetic core, and 1 layer is wound clockwise to form the second primary main winding Np2, and the number of turns of the second primary main winding Np2 is 10 turns. After forming the second primary main winding Np2, the output winding Ns is formed on the second primary main winding Np2. Among them, the number of turns of the output winding Ns is 5 turns. At this time, the common mode current balance is achieved inside the transformer.

[0051] Will Figure 8 and Fig. 9 By comparison, the sum of the number of turns of the first primary main winding Np1 and the number of turns of the second primary main winding Np2 is equal to the total number of turns of the primary main winding Np before the improvement. However, due to Fig. 9 The common mode current balance is achieved without setting a shielding layer, thus reducing the transformer cost. Fig. 9 The copper wire diameter of the first primary main winding Np1 is greater than Figure 8 The diameter of the copper wire of the main winding Np on the original side, that is, the copper wire becomes thicker, thereby reducing the impedance of the transformer.

[0052] In the specific implementation, continue to refer to Figure 4 The primary controller U11 may also be provided with a power supply terminal VDD, and the second primary main winding Np2 is connected to the power supply terminal VDD of the primary controller U11 to supply power to the primary controller U11. At this time, the second primary main winding Np2 may supply power to the primary controller U11.

[0053] In one embodiment, the primary control and power conversion circuit 42 may also include: a rectifier circuit and an energy storage subcircuit, wherein the rectifier circuit is used to rectify the voltage provided by the second primary main winding Np2, and the energy storage subcircuit is used to store the rectified voltage of the rectifier circuit and provide it to the power supply terminal VDD of the primary controller U11.

[0054] In one embodiment, referring to Figure 4 The energy storage subcircuit may include: a first capacitor C1 and a second capacitor C2, the first capacitor C1 and the second capacitor C2 are connected in parallel. One end of the first capacitor C1 and the second capacitor C2 is connected to the power supply terminal VDD of the primary controller U11, and the other end is connected to the opposite end B of the second primary main winding Np2.

[0055] The rectifier circuit may include a rectifier diode D1 and a fifth resistor R5 connected in series. The anode of the rectifier diode D1 is grounded, and the other end of the fifth resistor R5 is connected to the power supply terminal VDD of the primary controller U11. The voltage of the second primary main winding Np2 is rectified by the rectifier diode D1 and the fifth resistor R5 and provided to the primary controller U11.

[0056] exist Figures 10 to 13 In the illustrated embodiment, the primary controller and the power switch are integrated in the same power conversion chip U1. At this time, in the power conversion chip U1, one end of the power switch serves as the switch end SW of the power conversion chip U1, and the other end of the power switch is connected to the ground end GND of the primary controller. Figures 11 to 13 The output circuit is not shown.

[0057] In another embodiment, referring to Fig.10 , the energy storage subcircuit may only include the first capacitor C1. One end of the first capacitor C1 is connected to the power supply terminal VDD of the power supply terminal of the power conversion chip U1, and the other end is connected to the opposite end B of the second primary main winding Np2. Fig.10 In the figure, the charging path is: Np2à C àD1àR5àC1àNp2àB. C represents the same-name terminal of the second primary main winding Np2.

[0058] In another embodiment, referring to Fig.11 The rectifier circuit may only include: a rectifier diode D1. The anode of the rectifier diode D1 is grounded, and the cathode is connected to the power supply terminal of the power conversion chip U1.

[0059] In one embodiment of the present invention, the primary side control and power conversion circuit 42 may further include: a starting resistor; one end of the starting resistor is connected to the input circuit, and the other end is connected to the energy storage subcircuit, for charging the energy storage subcircuit to start the primary side controller.

[0060] Specifically, refer to Figure 4 The startup resistor includes: a first resistor R1 and a second resistor R2 connected in series, one end of the first resistor R1 is connected to the output end of the input circuit 41, and the other end is connected to the first capacitor C1 and the second capacitor C2, and is used to charge the first capacitor C1 and the second capacitor C2. After the charging voltage of the first capacitor C1 and the second capacitor C2 reaches the startup voltage of the primary controller U11, the primary controller U11 starts to work.

[0061] In other embodiments, the startup resistor may also include only one resistor or multiple resistors connected in series, which will not be described in detail here.

[0062] In a specific implementation, the primary controller also has a control signal terminal, and the second primary main winding is also connected to the control signal terminal of the primary controller for providing a control signal to the primary controller so that the primary controller can perform control operations.

[0063] Reference Figure 4 When the primary controller U11 and the power switch Q1 are independently configured, the second primary main winding Np2 can be connected to the control signal terminal DMG of the primary controller U11, thereby providing a control signal to the control signal terminal DMG of the primary controller U11.

[0064] Specifically, the control signal terminal DMG of the primary controller U11 can be connected to the second primary main winding Np2 through a voltage sampling subcircuit. The voltage sampling subcircuit may include a third resistor R3 and a fourth resistor R4. One end of the third resistor R3 is connected to the control signal terminal DMG, and the other end is connected to the same-name terminal of the second primary main winding Np2. One end of the fourth resistor R4 is connected to the control signal terminal DMG, and the other end is connected to the opposite-name terminal of the second primary main winding Np2.

[0065] The third resistor R3 and the fourth resistor R4 form a resistor network, through which the primary side controller U11 can collect the voltage signal from the second primary side main winding Np2. The voltage of the second primary side main winding Np2 is related to the voltage on the output winding Ns. By collecting the voltage signal of the second primary side main winding Np2, the on-off of the power switch tube can be controlled based on the voltage signal, and finally the on-off of the power switch tube affects the size of the output voltage, thereby realizing the primary side feedback control (Primary Side Regulator, PSR).

[0066] Reference Figures 10 to 13 When the primary side controller U11 and the power switch Q1 are integrated in the power conversion chip U1, at this time, the control signal terminal DMG of the primary side controller U11 serves as the control signal terminal DMG of the power conversion chip U1. A voltage sampling subcircuit can still be set between the power conversion chip U1 and the second primary side main winding Np2 to collect the voltage signal of the second primary side main winding Np2 to realize primary side feedback control.

[0067] In a specific implementation, based on the input of the control signal terminal DMG, the primary side controller U11 or the power conversion chip U1 can also detect signals such as output voltage, input voltage, valley bottom, etc.

[0068] In some embodiments, the primary control and power conversion circuit may further include: a current acquisition subcircuit. One end of the current acquisition subcircuit is connected to the power switch tube, and the other end is connected to the second primary main winding Np2. The current acquisition subcircuit can be used to acquire the current flowing through the power switch tube, thereby monitoring the current of the power switch tube.

[0069] Specifically, refer to Figure 4 , the current acquisition subcircuit may include: a sampling resistor Rcs. The sampling resistor Rcs may be arranged outside the primary controller U11. At this time, one end of the sampling resistor Rcs is connected to the current sampling terminal CS of the primary controller U11, and the other end is connected to the opposite end of the second primary main winding Np2, so that the opposite end of the second primary main winding Np2 is indirectly connected to the power switch Q1.

[0070] Reference Fig.12 When the primary side controller U11 and the power switch are integrated in the power conversion chip U1, the current sampling terminal CS of the primary side controller U11 can be used as the current sampling terminal CS of the power conversion chip U1, thereby realizing the connection with the sampling resistor Rcs.

[0071] In some embodiments, reference Fig.10 , Fig.11 and Fig.13 , the sampling resistor Rcs can also be integrated inside the power conversion chip U1. Inside the power conversion chip U1, the sampling resistor Rcs is still connected to the power switch tube.

[0072] In some embodiments, reference Figure 4 , Fig.11 and Fig.13 , the primary side control and power conversion circuit may further include: a feedback subcircuit. The feedback subcircuit may include: an optocoupler Q2. Accordingly, the primary side controller U11 and the power conversion chip U1 may be provided with a feedback terminal FB, and the feedback terminal FB is connected to the opposite-name terminal B of the second primary main winding Np2 through the optocoupler Q2. Correspondingly, an optocoupler should also be provided in the output circuit 43. Through the coupling between the optocouplers, the monitoring result of the output voltage can be obtained, which is then fed back to the primary side controller U11 or the power conversion chip U1 to realize the secondary side feedback control (Secondary Side Regulator, SSR).

[0073] In some embodiments, Fig.10 and Fig.12 As shown, the optocoupler Q2 can be integrated into the power conversion chip U1.

[0074] The flyback converter in the embodiment of the present invention and the flyback converter before improvement are tested under different input voltages, wherein the flyback converter in the embodiment of the present invention and the flyback converter before improvement have the same circuit structure, the capacitance, inductance, etc. in the circuit are the same, and the number of turns of the primary main winding of the transformer and the number of turns and inductance of the output winding are also the same. The difference is that the first primary main winding of the flyback converter in the embodiment of the present invention is connected in series with the second primary main winding through a power switch string.

[0075] Table 1

[0076] Among them, Table 1 is the test data of the flyback converter before improvement at input voltages of 90V and 115V, and Table 2 is the test data of the flyback converter in the embodiment of the present invention at input voltages of 90V and 115V. The test data include: input power, output voltage, output current, output power, board efficiency, and average board efficiency. Output efficiency refers to the ratio of the output power of the flyback converter to the input power.

[0077] Table 2

[0078] Comparing the test data in Table 1 with the test data in Table 2, it can be seen that the output efficiency is significantly increased when the transformer structure in the embodiment of the present invention is used, when the input voltage and output current are the same. For example, when the input voltage is 90V and the output current is 3.2A, the output efficiency of the flyback converter before the improvement is 86.36%, while the output efficiency of the flyback converter in the embodiment of the present invention is 86.91%, and the output efficiency is increased by 0.55%. When the input voltage is 115V, the average output efficiency of the flyback converter before the improvement is 88.29%, while the average output efficiency of the flyback converter in the embodiment of the present invention is 89.34%, and the output efficiency is increased by 1.05% on average.

[0079] That is to say, by using the flyback converter in the embodiment of the present invention, under the same circuit structure, due to the change in the transformer structure, the leakage inductance can be effectively optimized, the voltage conversion efficiency can be improved, and then the output efficiency can be improved.

[0080] As can be seen from the above content, in the flyback converter in the embodiment of the present invention, the first primary main winding and the second primary main winding are connected in series through a power switch. This change in connection mode can reduce electromagnetic interference caused by excessive voltage variation. In addition, the transformer structure can be simplified, leakage inductance can be optimized, output efficiency can be improved, operating temperature can be reduced, transformer cost can be reduced, and transformer stability can be increased.

[0081] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A flyback converter, characterized in that: include: Input circuit, primary side control and power conversion circuit and output circuit, wherein: The input circuit is used to convert AC voltage into DC voltage; The primary side control and power conversion circuit is used to perform power conversion on the DC voltage; The output circuit is used to sense and output the voltage after power conversion; Wherein, the primary control and power conversion circuit includes: a first primary main winding, a power switch and a second primary main winding; when the power switch is closed, the first primary main winding and the second primary main winding are connected in series through the power switch.

2. The flyback converter according to claim 1, characterized in that: The same-name end of the first primary main winding is connected to one end of the power switch; the opposite-name end of the second primary main winding is directly or indirectly connected to the other end of the power switch.

3. The flyback converter according to claim 2, characterized in that: The output circuit comprises: an output winding; the first primary main winding, the second primary main winding and the output winding are wound layer by layer on the same magnetic core to form a transformer.

4. The flyback converter according to claim 3, characterized in that: The ratio of the number of turns of the first primary main winding to the number of turns of the second primary main winding is used to balance the common mode current of the transformer.

5. The flyback converter according to any one of claims 1 to 4, characterized in that: The primary control and power conversion circuit further includes: a primary controller; the second primary main winding is connected to the power supply end of the primary controller to supply power to the primary controller.

6. The flyback converter according to claim 5, characterized in that: The primary control and power conversion circuit also includes: a rectifier circuit and an energy storage subcircuit; the rectifier circuit is used to rectify the voltage provided by the second primary main winding, and the energy storage subcircuit is used to store the voltage rectified by the rectifier circuit and provide it to the power supply end of the primary controller.

7. The flyback converter according to claim 6, characterized in that: The rectifier circuit includes: a rectifier diode; or a rectifier diode and a fifth resistor connected in series.

8. The flyback converter according to claim 6, characterized in that: The energy storage subcircuit includes: a first capacitor; or a first capacitor and a second capacitor connected in parallel.

9. The flyback converter according to claim 8, characterized in that: The primary side control and power conversion circuit further includes: a starting resistor; one end of the starting resistor is connected to the input circuit, and the other end is connected to the first capacitor and the second capacitor.

10. The flyback converter according to any one of claims 1 to 4, characterized in that: The primary control and power conversion circuit also includes: a primary controller; the second primary main winding is also connected to the control signal end of the primary controller, for providing a control signal to the primary controller so that the primary controller can perform control operations.

11. The flyback converter according to claim 10, characterized in that: The primary control and power conversion circuit also includes: a third resistor and a fourth resistor, the control signal end of the primary controller is connected to the same-name end of the second primary main winding through the third resistor, and the control signal end of the primary controller is connected to the opposite-name end of the second primary main winding through the fourth resistor.

12. The flyback converter according to claim 10, characterized in that: The primary control and power conversion circuit also includes: a current collection subcircuit, one end of which is connected to the power switch tube, and the other end of which is connected to the second primary main winding.

13. The flyback converter according to claim 10, characterized in that: The primary control and power conversion circuit further includes: a feedback subcircuit, one end of which is connected to the second primary main winding and the other end is connected to the primary controller, for monitoring the output voltage of the flyback converter.

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