Flyback converter
By connecting the first primary winding and the second primary winding in series in the flyback converter, and adjusting the number of winding turns to balance the common-mode current, the electromagnetic interference problem of the flyback converter is solved, the efficiency of the transformer is improved and the cost is reduced.
Patent Information
- Application Number
- CN202520411610.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Priority Date
- 2024-12-09
- Filing Date
- 2025-03-10
- Publication Date
- 2026-03-20
- Estimated Expiration
- 2035-03-10
AI Technical Summary
Existing flyback converters suffer from electromagnetic interference (EMI) problems, especially after adding shielding windings inside the transformer, which affects coupling performance, efficiency, and cost.
The first primary winding and the second primary winding are connected in series by a power switch to decompose the noise source of the transformer main winding. The common-mode current is balanced by adjusting the number of winding turns and the connection method. The shielding layer is removed to achieve the balance of the internal common-mode current.
It reduces electromagnetic interference caused by excessive voltage fluctuations, optimizes the coupling performance and conversion efficiency of the transformer, reduces costs, and improves output efficiency.
Smart Images
Figure CN224021623U_ABST
Abstract
Description
[0001] The present application claims priority to the Chinese patent application No. 202411795224.6, filed on December 9, 2024, and entitled “Flyback converter”, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD
[0002] The utility model relates to switching power supply technical field, concretely relates to a flyback converter. BACKGROUND
[0003] Flyback converter is widely used in AC / DC and DC / DC conversion, and provides insulation isolation between input stage and output stage, is a kind of switching power supply, and is widely used in various consumer electronics. High efficiency, low noise scheme is extremely important to reduce system cost and improve user experience.
[0004] However, in the topology structure of the existing flyback converter, there is a certain electromagnetic interference (EMI) problem. UTILITY MODEL CONTENT
[0005] The problem to be solved by the utility model is: how to reduce the electromagnetic interference of flyback converter.
[0006] To solve the above problems, the utility model embodiment provides a flyback converter, the flyback converter includes: input circuit, primary side control and power conversion circuit and output circuit, wherein:
[0007] The input circuit is used to convert AC voltage into DC voltage;
[0008] The primary side control and power conversion circuit are used to perform power conversion on the DC voltage;
[0009] The output circuit is used to inductively obtain power-converted voltage and output;
[0010] The primary side control and power conversion circuit include: first primary side main winding, power switch and 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.
[0011] In a possible embodiment, the same name end of the first primary side main winding is connected with one end of the power switch, and the opposite name end of the second primary side main winding is directly or indirectly connected with the other end of the power switch.
[0012] In a possible embodiment, the output circuit comprises: an output winding; the first primary main winding, the second primary main winding and the output winding are sequentially wound on the same magnetic core to form a transformer.
[0013] In a possible embodiment, a ratio of the number of turns of the first primary main winding to the number of turns of the second primary main winding is configured to balance common-mode current of the transformer.
[0014] In a possible embodiment, the primary control and power conversion circuit further comprises: a primary controller; and the second primary main winding is connected to a power supply end of the primary controller, and configured to supply power to the primary controller.
[0015] In a possible embodiment, the primary control and power conversion circuit further comprises: a rectifier sub-circuit and an energy storage sub-circuit; the rectifier sub-circuit is configured to rectify a voltage provided by the second primary main winding; and the energy storage sub-circuit is configured to store the rectified voltage and provide the rectified voltage to the power supply end of the primary controller.
[0016] In a possible embodiment, the rectifier sub-circuit comprises: a rectifier diode; or a rectifier diode and a fifth resistor connected in series.
[0017] In a possible embodiment, the energy storage sub-circuit comprises: a first capacitor; or a first capacitor and a second capacitor connected in parallel.
[0018] In a possible embodiment, the primary control and power conversion circuit further comprises: a start-up resistor; one end of the start-up resistor is connected to the input circuit, and the other end of the start-up resistor is connected to the first capacitor and the second capacitor.
[0019] In a possible embodiment, the primary control and power conversion circuit further comprises: a primary controller; and the second primary main winding is further connected to a control signal end of the primary controller, and configured to provide a control signal to the primary controller to enable the primary controller to perform a control operation.
[0020] In a possible embodiment, the primary control and power conversion circuit further comprises: a third resistor and a fourth resistor; the control signal end of the primary controller is connected to a 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 a different-name end of the second primary main winding through the fourth resistor.
[0021] In a possible embodiment, the primary control and power conversion circuit further comprises: a current acquisition sub-circuit; one end of the current acquisition sub-circuit is connected to the power switch tube; and the other end of the current acquisition sub-circuit is connected to the second primary main winding.
[0022] In one possible embodiment, the primary-side control and power conversion circuit further includes a feedback sub-circuit, one end of which is connected to the second primary-side main winding and the other end of which is connected to the primary-side controller, for monitoring the output voltage of the flyback converter.
[0023] Compared with the prior art, the technical solution of this utility model embodiment has the following advantages:
[0024] By applying the solution of this utility model, when the power switch is closed, since the first primary winding and the second primary winding are connected in series through the power switch, the second primary winding can share the voltage of the transformer primary winding. Compared with setting only one primary winding, the noise source of the transformer primary winding can be decomposed into two parts, including the noise generated by the first primary winding and the noise generated by the second primary winding. After decomposition, the voltage change of each noise source is reduced, thereby reducing the electromagnetic interference caused by excessive voltage change.
[0025] Furthermore, the same-name terminal of the first primary winding is connected to one end of the power switch, while the opposite-name terminal of the second primary winding is connected to the other end of the power switch. Thus, when the power switch is closed, the voltage at the same-name terminal of the first primary winding decreases, but the voltage at the opposite-name terminal of the second primary winding increases. This allows the common-mode current generated by the second primary winding to be in the opposite direction to that generated by the first primary winding, which is beneficial for balancing the common-mode current inside the transformer and thus helps to solve the EMI problem caused by the imbalance of common-mode current. Attached Figure Description
[0026] Figure 1 This is a topology diagram of a flyback converter in the prior art;
[0027] Figure 2 This is a schematic diagram of the internal structure of a transformer in the prior art;
[0028] Figure 3 This is a schematic diagram illustrating the change in the direction of the common-mode current inside a transformer in the prior art;
[0029] Figure 4 This is a topology diagram of a flyback converter according to an embodiment of the present invention;
[0030] Figure 5 yes Figure 4 A schematic diagram of the voltage variation curves of the first primary winding and the second primary winding;
[0031] Figure 6 This is a schematic diagram of the internal structure of a transformer according to an embodiment of this utility model;
[0032] Figure 7is a schematic diagram of the change of common mode current direction in the transformer in the embodiment of the utility model;
[0033] Figure 8 is a winding schematic diagram of each winding in the transformer;
[0034] Figure 9 is a winding schematic diagram of each winding in the transformer in the embodiment of the utility model;
[0035] Figure 10 is another topology structure diagram of the flyback converter in the embodiment of the utility model;
[0036] Figure 11 is still another topology structure diagram of the flyback converter in the embodiment of the utility model;
[0037] Figure 12 is still another topology structure diagram of the flyback converter in the embodiment of the utility model;
[0038] Figure 13 is another topology structure diagram of the flyback converter in the embodiment of the utility model. DETAILED DESCRIPTION
[0039] Figure 1 is a topology structure of the existing flyback converter. Referring to Figure 1 , the flyback converter can include: an input circuit 11, a primary side control and power conversion circuit 12 and an output circuit 13.
[0040] The input circuit 11 includes a primary side rectifier 111 and a filter sub-circuit 112. After the AC voltage is rectified by the primary side rectifier 111, the rectified voltage is filtered by the filter sub-circuit 112 composed of a first electrolytic capacitor and an inductor, and finally a DC voltage is obtained, and the obtained DC voltage is provided to the primary side control and power conversion circuit 12.
[0041] The primary side control and power conversion circuit 12 includes a transformer primary side main winding Np, a transformer auxiliary winding Na, a primary side controller and a power switch connected in series. The primary side controller and the power switch can be integrated in a power conversion chip U1, and the power switch is located between a switch pin (SW) and a ground pin (GND). The transformer auxiliary winding Na also has an auxiliary rectifier D1 and a second electrolytic capacitor C1 on one side, and the auxiliary rectifier D1 is located at the positive terminal 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 transformer primary side main winding Np, and the primary side controller can control the on-off of the power switch, thereby realizing power conversion.
[0042] 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 transmitted to the output winding Ns in a magnetic field induction manner, and through the secondary rectifier and the output capacitor, a stable DC output is achieved.
[0043] In the flyback converter of the above topology, with reference to Figure 3 When the primary side controller controls the power switch to be turned on, the power conversion chip U1 switch pin (that is, the connection end of the power switch and the transformer primary main winding Np) will be short-circuited to the ground. At this time, taking the common-mode current flowing into the output winding Ns as an example, the voltage V_Np at the like-named end of the transformer primary main winding Np and the voltage V_Na at the like-named end of the transformer auxiliary winding Na will be lowered, thereby generating a negative common-mode current. The voltage V_Ns at the unlike-named end of the output winding Ns will be raised, thereby also generating a negative common-mode current.
[0044] 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 shielding winding is needed to generate a positive common-mode current to avoid electromagnetic interference caused by unbalanced common-mode current.
[0045] Specifically, with reference to Figure 2 Inside the transformer, a shielding winding is added between the primary main winding Np and the output winding Ns to balance the common-mode current. When the primary side is turned on, the voltage V_Nss at the like-named end of the shielding winding will be lowered, and a positive common-mode current will be generated (as shown in Figure 3 At this time, the positive common-mode current generated by the shielding winding will balance the negative common-mode currents generated by the primary main winding Np, the auxiliary winding Na, and the output winding Ns.
[0046] However, due to the addition of the shielding winding inside the transformer, the primary main winding Np and the output winding Ns cannot be closely attached, thereby affecting the coupling performance between the primary main winding Np and the output winding Ns, causing the transformer leakage inductance to be large, and even affecting the voltage conversion efficiency and temperature of the transformer. Moreover, whether the sandwich or the order winding method is used, the transformer will be affected to a certain extent. Furthermore, due to the addition of the shielding winding inside the transformer, the number of layers inside the transformer is increased, causing the process to be complex, and the cost of the transformer to be increased.
[0047] In addition, even if the shielding winding is added inside the transformer of the flyback converter with the above topology, when the power switch is turned off, the voltage at the switch pin (UI-SW) of the power converter U1 changes from zero to (Vin_dc+nVo). Wherein, Vin_dc is the direct current 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) as the main noise source, the voltage at the switch pin (UI-SW) of the power converter U1 changes with time (dv / dt) is large, so EMI problem will still occur.
[0048] To solve the problem, the utility model provides a kind of flyback converter, in the flyback converter, when power switch is closed, because first primary main winding and the second primary main winding are connected in series by power switch, whereby the noise source of transformer main winding can be decomposed into first primary main winding and second primary main winding two parts, the voltage variation of each noise after decomposition reduces, so that the electromagnetic interference generated by the voltage variation being too large can be reduced.
[0049] In order to make the above-mentioned purpose, features and advantages of the utility model more obvious and easy to understand, the specific embodiments of the utility model are described in detail below with reference to the drawings.
[0050] The utility model embodiment provides a kind of flyback converter, the flyback converter can include: input circuit, primary side control and power conversion circuit and output circuit.
[0051] The input circuit is used to convert alternating voltage into direct current voltage;
[0052] The primary side control and power conversion circuit are used to power conversion to the direct current voltage;
[0053] The output circuit is used to inductively obtain voltage after power conversion and output;
[0054] Wherein, the primary side control and power conversion circuit include: first primary main winding, power switch and 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 by the power switch.
[0055] With the above flyback converter, when the power switch is closed, the first primary main winding and the second primary main winding are connected in series by the power switch, whereby the noise source of transformer main winding can be decomposed into two parts, which are 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, so that the EMI problem caused by the voltage variation being too large can be reduced.
[0056] In a specific implementation, the primary side control and power conversion circuit can include a primary side controller and a power switch. The primary side controller and the power switch can be independently arranged (as shown in Figure 4 ), or integrated in the same power conversion chip (as shown in Figure 10 to Figure 13 ).
[0057] The flyback converter in the embodiments of the present application will be described in detail below in combination with specific circuit structures.
[0058] Figure 4 FIG. 1 is a schematic diagram of the topology structure of the flyback converter 40 in an embodiment of the present application, and the flyback converter 40 can include an input circuit 41, a primary side control and power conversion circuit 42, and an output circuit 43. Figure 4
[0059] The input circuit 41 can include a primary side rectifier 411 and a filter sub-circuit 412. The primary side rectifier 411 can be implemented by a rectifier bridge. The filter sub-circuit 412 can include electrolytic capacitors, inductors, and the like. After the AC voltage is rectified by the primary side rectifier 411, the rectified voltage is filtered by the filter sub-circuit 412 to obtain a DC voltage Vin_dc.
[0060] The output circuit 43 can include an output winding Ns, a secondary side rectifier, and an output capacitor. The voltage induced by the output winding Ns is rectified by the secondary side rectifier and then output by the output capacitor.
[0061] In a specific implementation, the primary side control and power conversion circuit 42 can include a first primary side main winding Np1, a power switch Q1, and a second primary side main winding Np2. When the power switch Q1 is closed, the first primary side main winding Np1 is connected in series with the second primary side main winding Np2 through the power switch Q1. The second primary side main winding Np2 and the first primary side main winding Np1 form the main winding of the transformer T1. The second primary side main winding Np2 and the first primary side main winding Np1 jointly undertake the energy storage function of the transformer, so that the current density in the transformer is more balanced, and the utilization rate of the transformer is higher.
[0062] The primary side control and power conversion circuit 42 can further comprise a primary side controller U11. The primary side controller U11 further has a gate end Gate and a ground end GND. The gate end Gate is connected with the gate of the power switch Q1, thereby controlling the on-off of the power switch Q1. The ground end GND is connected with one end B of the second primary side main winding Np2. When the power switch Q1 is closed, the voltage of the end B of the second primary side main winding Np2 changes, so the end B of the second primary side main winding Np2 is a dynamic node, thereby the noise source of the primary side main winding of the flyback converter can be divided into two parts, which are the noise generated by the first primary side main winding Np1 and the noise generated by the second primary side main winding Np2.
[0063] Wherein, referring to Figure 5 , when the power switch Q1 is closed, the voltage of the same name end A of the first primary side main winding Np1 changes from zero to (n1Vo+Vin_dc), and the voltage of the end B of the second primary side main winding Np2 connected with the power switch Q1 changes from zero to V1. Wherein n1 is the ratio of the number of turns of the first primary side main winding Np1 to the number of turns of the output winding Ns. Since the number of turns of the first primary side main winding Np1 is smaller than the number of turns of the primary side main winding Np in Figure 1 , and n1 Figure 1 , so the voltage change of the same name end A of the first primary side main winding Np1 is smaller than the voltage change of the same name end of the primary side main winding Np in
[0064] Therefore, by connecting the first primary side main winding Np1 and the second primary side main winding Np2 in series, the electromagnetic interference generated by the excessive voltage change of the end of the primary side main winding connected with the primary side controller U11 can be greatly reduced.
[0065] In an embodiment of the present application, in order to avoid the electromagnetic interference generated by the unbalance of the common mode current inside the transformer T1, referring to Figure 4 , the same name end A of the first primary side main winding Np1 can be connected with one end of the power switch Q1, and the different name end B of the second primary side main winding Np2 can be directly connected with the other end of the power switch Q1.
[0066] At this time, the same name end A of the first primary side main winding Np1 and the different name end B of the second primary side main winding Np2 are out of phase points, thereby the direction of the common mode current generated by the first primary side main winding Np1 can be opposite to the direction of the common mode current generated by the second primary side main winding Np2, and the direction of the noise generated by the first primary side main winding Np1 can be opposite to the direction of the noise generated by the second primary side main winding Np2, thereby the balance of the common mode current inside the transformer T1 can be facilitated, and the electromagnetic interference problem can be reduced.
[0067] The common-mode current generated by the second primary main winding Np2 is opposite to the common-mode current generated by the first primary main winding Np1, and therefore, in an embodiment, the first primary main winding Np1, the second primary main winding Np2 and the output winding Ns are sequentially wound on the same magnetic core to form the transformer T1.
[0068] Specifically, referring to Figure 6 The copper wire can be wound on the magnetic core as the first primary main winding Np1. Then, the copper wire is wound on the first primary main winding Np1 to form the second primary main winding Np2. Finally, the copper wire is wound on the second primary main winding Np2 to form the output winding Ns. The first primary main winding Np1 is in contact with the second primary main winding Np2, and the second primary main winding Np2 is in contact with the output winding Ns. The transformer T1 does not need a shielding layer, and the second primary main winding Np2 provides the reverse common-mode current.
[0069] The common-mode current flowing into the output winding Ns is the positive common-mode current, and referring to Figure 7 When the power switch Q1 is closed, the voltage V_Np1 of the same name end A of the first primary main winding Np1 decreases, thereby generating the negative common-mode current. The voltage V_Np2 of the different name end of the second primary main winding Np2 increases, thereby generating the positive common-mode current. The voltage V_Ns of the different name end of the output winding Ns increases, thereby generating the negative common-mode current. In this way, the common-mode current in the transformer T1 can be balanced more favorably.
[0070] In an embodiment of the utility model, the winding turns ratio of the first primary main winding Np1 and the second primary main winding Np2 can be adjusted to balance the common-mode current of the transformer T1. At this time, the winding turns of the second primary main winding Np2 can be adjusted to change the size of the positive common-mode current generated in the transformer T1, and the winding turns of the first primary main winding Np1 can be adjusted to change the size of the negative common-mode current generated in the transformer T1. Finally, the positive common-mode current generated in the transformer T1 is equal to the negative common-mode current generated in the transformer T1, and the common-mode currents are offset each other.
[0071] In an embodiment of the utility model, the sum of the winding turns of the first primary main winding and the winding turns of the second primary main winding is equal to the winding turns of the original primary main winding before the improvement. In this way, the number of copper wire layers in 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. The coupling between the windings in the transformer is better, and the conversion efficiency of the transformer is improved, thereby improving the output efficiency of the transformer.
[0072] For example, Figure 8The internal structure diagram of the transformer before improvement is shown in Fig. 1. Figure 8 In the improved transformer, 0.23 mm polyurethane enameled wire (2UEW) is adopted to start from the 7th pin (7(s)) of the magnetic core, to wind 2 layers clockwise, and to wind out from the 4th pin (4(s)) of the magnetic core, to form the primary main winding Np, and each layer is wound for 23 turns (Ts), and the total turns of the primary main winding Np are 46 turns.
[0073] Figure 9 The internal structure diagram of the transformer before improvement is shown in Fig. 1. Figure 9 In the improved transformer, 0.23 mm polyurethane enameled wire (2UEW) is adopted to start from the 7th pin (7(s)) of the magnetic core, to wind 2 layers clockwise, and to wind out from the 4th pin (4(s)) of the magnetic core, to form the primary main winding Np, and each layer is wound for 23 turns (Ts), and the total turns of the primary main winding Np are 46 turns.
[0074] Figure 8 Figure 9 It can be known by comparison that the sum of the turns of the first primary main winding Np1 and the turns of the second primary main winding Np2 is equal to the total turns of the primary main winding Np before improvement, but since Figure 9 does not set the shielding layer to achieve common-mode current balance, the cost of the transformer can be reduced. Figure 9 In the improved transformer, the copper wire diameter of the first primary main winding Np1 is greater than that of the primary main winding Np in the transformer before improvement, that is, the copper wire is thickened, so that the impedance of the transformer can be reduced. Figure 8
[0075] In the specific implementation, continuing to refer to Figure 4 The primary controller U11 can also be provided with a power supply end VDD, the second primary main winding Np2 is connected with the power supply end VDD of the primary controller U11, and is used to supply power for the primary controller U11.
[0076] In an embodiment, the primary side control and power conversion circuit 42 can further comprise a rectifier sub-circuit for rectifying the voltage provided by the second primary side main winding Np2, and a storage sub-circuit for storing the rectified voltage and providing a power supply for the primary side controller U11.
[0077] In an embodiment, referring to Figure 4 , the storage sub-circuit can comprise a first capacitor C1 and a second capacitor C2 connected in parallel. One end of the first capacitor C1 and the second capacitor C2 is connected to the power supply end VDD of the primary side controller U11, and the other end is connected to the opposite end B of the second primary side main winding Np2.
[0078] The rectifier sub-circuit can comprise 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 end VDD of the primary side controller U11. The voltage of the second primary side main winding Np2 is rectified by the rectifier diode D1 and the fifth resistor R5, and then provided to the primary side controller U11.
[0079] In Figure 10 to Figure 13 the embodiment shown, the primary side 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 is used 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 side controller. In Figure 11 to Figure 13 , the output circuit is not shown.
[0080] In another embodiment, referring to Figure 10 , the storage sub-circuit can only comprise a first capacitor C1. One end of the first capacitor C1 is connected to the power supply end VDD of the power supply end of the power conversion chip U1, and the other end is connected to the opposite end B of the second primary side main winding Np2. At this time, in Figure 10 , the charging path is: Np2 C D1R5C1Np2B. Wherein, C represents the same end of the second primary side main winding Np2.
[0081] In another embodiment, referring to Figure 11 , the rectifier sub-circuit can only comprise a rectifier diode D1. The anode of the rectifier diode D1 is grounded, and the cathode is connected to the power supply end of the power conversion chip U1.
[0082] In an embodiment of the utility model, the primary side control and power conversion circuit 42 can further comprise a starting resistor, one end of the starting resistor is connected to the input circuit, the other end is connected to the storage sub-circuit, and is used for charging the storage sub-circuit to start the primary side controller.
[0083] Specifically, referring to Figure 4 , the starting resistor comprises: a first resistor R1 and a second resistor R2 connected in series, one end of the first resistor R1 is connected with the output end of the input circuit 41, and the other end is connected with the first capacitor C1 and the second capacitor C2, for charging 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 starting voltage of the primary side controller U11, the primary side controller U11 starts to work.
[0084] In other embodiments, the starting resistor can also include only one resistor or a plurality of series-connected resistors, which are not described here.
[0085] In specific implementation, the primary side controller also has a control signal end, and the second primary side main winding is also connected with the control signal end of the primary side controller, for providing a control signal for the primary side controller to perform control operation.
[0086] Referring to Figure 4 , when the primary side controller U11 and the power switch Q1 are independently arranged, the second primary side main winding Np2 can be connected with the control signal end DMG of the primary side controller U11, thereby providing a control signal for the control signal end DMG of the primary side controller U11.
[0087] Specifically, the control signal end DMG of the primary side controller U11 can be connected with the second primary side main winding Np2 through a voltage sampling sub-circuit. The voltage sampling sub-circuit can include a third resistor R3 and a fourth resistor R4. One end of the third resistor R3 is connected with the control signal end DMG, and the other end is connected with the same end of the second primary side main winding Np2. One end of the fourth resistor R4 is connected with the control signal end DMG, and the other end is connected with the different end of the second primary side main winding Np2.
[0088] 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, and 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 size of the output voltage is affected by the on-off of the power switch tube, realizing primary side feedback control (Primary Side Regulator, PSR).
[0089] Referring to Figure 10 to Figure 13When the primary side controller U11 is integrated with the power switch Q1 in the power conversion chip U1, at this time, the control signal end DMG of the primary side controller U11 serves as the control signal end DMG of the power conversion chip U1, and the voltage sampling sub-circuit between the power conversion chip U1 and the second primary side main winding Np2 can still be arranged to collect the voltage signal of the second primary side main winding Np2, so as to realize the primary side feedback control.
[0090] In a specific implementation, based on the input of the control signal end DMG, the primary side controller U11 or the power conversion chip U1 can also perform detection of output voltage, input voltage, valley bottom and the like.
[0091] In some embodiments, the primary side control and power conversion circuit can further include a current collection sub-circuit. One end of the current collection sub-circuit is connected with the power switch tube, and the other end is connected with the second primary side main winding Np2. The current collection sub-circuit can collect the current flowing through the power switch tube, so as to monitor the current of the power switch tube.
[0092] Specifically, referring to Figure 4 , the current collection sub-circuit can include a sampling resistor Rcs. The sampling resistor Rcs can be arranged outside the primary side controller U11. At this time, one end of the sampling resistor Rcs is connected with the current sampling end CS of the primary side controller U11, and the other end is connected with the opposite-phase end of the second primary side main winding Np2, so that the opposite-phase end of the second primary side main winding Np2 is indirectly connected with the power switch Q1.
[0093] Referring to Figure 12 , when the primary side controller U11 is integrated with the power switch in the power conversion chip U1, the current sampling end CS of the primary side controller U11 can serve as the current sampling end CS of the power conversion chip U1, so as to realize the connection with the sampling resistor Rcs.
[0094] In some embodiments, referring to Figure 10 , Figure 11 and Figure 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 with the power switch tube.
[0095] In some embodiments, referring to Figure 4 , Figure 11 and Figure 13The primary side control and power conversion circuit can further comprise a feedback sub-circuit. The feedback sub-circuit can comprise an optocoupler Q2. Accordingly, the primary side controller U11 and the power conversion chip U1 can be provided with a feedback end FB connected with the non-identical end B of the second primary side main winding Np2 through the optocoupler Q2. Accordingly, the output circuit 43 should also be provided with an optocoupler. Through the coupling between the optocouplers, the monitoring result of the output voltage can be obtained, so as to be fed back to the primary side controller U11 or the power conversion chip U1, thereby realizing the secondary side feedback control (SSR).
[0096] In some embodiments, as shown in Figure 10 and Figure 12 The optocoupler Q2 can be integrated in the power conversion chip U1.
[0097] The flyback converter in the embodiment of the utility model and the flyback converter before improvement are tested under different input voltages, wherein the flyback converter in the embodiment of the utility model and the flyback converter before improvement have the same circuit structure, and the values of capacitor, inductor in the circuit are all same, and the number of turns of the primary side main winding of the transformer and the number of turns and inductance of the output winding are also same, and the difference is that the first primary side main winding of the flyback converter in the embodiment of the utility model is connected in series with the second primary side main winding through the power switch string.
[0098] Table 1
[0099]
[0100] Among them, table 1 is the test data of the flyback converter before improvement under the input voltage of 90V and 115V, and table 2 is the test data of the flyback converter in the embodiment of the utility model under the input voltage of 90V and 115V. The test data includes input power, output voltage, output current, output power and board end efficiency, average value of board end efficiency. The output efficiency refers to the ratio of the output power of the flyback converter to the input power.
[0101] Table 2
[0102]
[0103] By comparing the test data in Table 1 with the test data in Table 2, it can be seen that, in the case of the same input voltage and output current, the output efficiency is obviously increased by using the transformer structure in the embodiment of the utility model. For example, when the input voltage is 90V and the output current is 3.2A, the output efficiency of the flyback converter before improvement is 86.36%, while the output efficiency of the flyback converter in the embodiment of the utility model 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 improvement is 88.29%, while the average output efficiency of the flyback converter in the embodiment of the utility model is 89.34%, and the average output efficiency is increased by 1.05%.
[0104] That is, by using the flyback converter in the embodiment of the utility model, under the same circuit structure, the leakage inductance can be effectively optimized, the voltage conversion efficiency can be improved, and the output efficiency can be improved due to the change of the transformer structure.
[0105] As can be seen from the above, the flyback converter in the embodiment of the utility model, the first primary main winding and the second primary main winding are connected in series through the power switch, and the change of the connection mode can reduce the electromagnetic interference caused by the excessive voltage variation. Moreover, the transformer structure can be simplified, the leakage inductance can be optimized, the output efficiency can be improved, the working temperature can be reduced, the cost of the transformer can be reduced, and the stability of the transformer can be increased.
[0106] Although the utility model discloses as above, the utility model is not limited to this. Any person skilled in the art, without departing from the spirit and scope of the utility model, can make various changes and modifications, therefore the protection scope of the utility model should be limited by the range defined in the claims.
Claims
1. A flyback converter, characterized in that, include: The circuit comprises an input circuit, a primary-side control and power conversion circuit, and an output circuit, wherein the output circuit includes an output winding; 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; The primary-side control and power conversion circuit includes: 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; the first primary-side main winding, the second primary-side main winding, and the output winding constitute a transformer.
2. The flyback converter as described in claim 1, characterized in that, The same-name terminal of the first primary winding is connected to one end of the power switch; the opposite-name terminal of the second primary winding is directly or indirectly connected to the other end of the power switch.
3. The flyback converter as described in claim 2, characterized in that, The output circuit includes: an output winding; the first primary winding, the second primary winding, and the output winding are successively bonded and wound on the same magnetic core to form a transformer.
4. The flyback converter as described in claim 3, characterized in that, The ratio of the number of turns in the first primary winding to the number of turns in the second primary winding is used to balance the common-mode current of the transformer.
5. The flyback converter as described in any one of claims 1 to 4, characterized in that, The primary-side control and power conversion circuit further includes: a primary-side controller; the second primary-side main winding is connected to the power supply terminal of the primary-side controller for supplying power to the primary-side controller.
6. The flyback converter as described in claim 5, characterized in that, The primary-side control and power conversion circuit further includes a rectifier circuit and an energy storage circuit; the rectifier circuit is used to rectify the voltage provided by the second primary-side main winding, and the energy storage circuit is used to store the voltage rectified by the rectifier circuit and provide it to the power supply terminal of the primary-side controller.
7. The flyback converter as described in 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 as described in claim 6, characterized in that, The energy storage sub-circuit includes: a first capacitor; or, a first capacitor and a second capacitor connected in parallel.
9. The flyback converter as described in 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-side control and power conversion circuit further includes: a primary-side controller; the second primary-side main winding is also connected to the control signal terminal of the primary-side controller, for providing control signals to the primary-side controller so that the primary-side controller can perform control operations.
11. The flyback converter as claimed in claim 10, characterized in that, The primary-side control and power conversion circuit further includes a third resistor and a fourth resistor. The control signal terminal of the primary-side controller is connected to the same-name terminal of the second primary-side main winding through the third resistor, and the control signal terminal of the primary-side controller is connected to the opposite-name terminal of the second primary-side main winding through the fourth resistor.
12. The flyback converter as described in claim 10, characterized in that, The primary-side control and power conversion circuit further includes a current acquisition sub-circuit, one end of which is connected to the power switching transistor and the other end is connected to the second primary-side main winding.
13. The flyback converter as described in claim 10, characterized in that, The primary-side control and power conversion circuit further includes a feedback sub-circuit, one end of which is connected to the second primary-side main winding and the other end is connected to the primary-side controller, for monitoring the output voltage of the flyback converter.