Flyback switching power supply control circuit

Abstract

The utility model discloses a flyback switching power supply control circuit, which comprises a PFC (Power Factor Correction) circuit, the primary side alternating current filtering and rectifying circuit is connected in series with the PFC circuit; a secondary side filtering and rectifying circuit; the common mode inductor TF1 is connected to the secondary side filtering and rectifying circuit; the circuit further comprises at least two transformers and RCD absorption circuits connected with the transformers respectively, the input ends of the transformers and the RCD absorption circuits are connected with the PFC circuit, the RCD absorption circuits are connected in series, and the output ends of the transformers are connected to the secondary side filtering and rectifying circuit. According to the high-power flyback circuit, heating of a single transformer can be greatly reduced, heat treatment is easier, the problems that a high-power flyback circuit transformer is high in leakage inductance and the voltage stress of an MOS tube is not easy to solve are solved, meanwhile, the manufacturing cost of a 200-600W switching power supply can be reduced, and the circuit structure is simpler and more convenient.

Description

Technical Field

[0001] The utility model relates to the technical field of switching power supplies, in particular to a flyback switching power supply control circuit. Background Art

[0002] Currently, 200-600W switching power supplies generally use forward circuits or LLC circuits. The traditional flyback circuit solution requires a larger transformer, and the transformer unit generates heat, and the heat dissipation cannot be solved, making it difficult to implement.

[0003] At the same time, the forward circuit requires an additional freewheeling inductor in addition to the transformer, which will reduce efficiency and increase costs. The LLC circuit solution also requires a resonant inductor in addition to the transformer, and the cost of its control chip is higher than that of the flyback circuit. Utility Model Content

[0004] The purpose of the present utility model is to address the deficiencies in the prior art and to provide a technical solution for a flyback switching power supply control circuit. The solution not only greatly reduces the heat generation of a single transformer, making heat treatment easier, but also solves the problems of high transformer leakage inductance and difficult-to-solve voltage stress of MOS tubes in high-power flyback circuits. At the same time, the solution can reduce the manufacturing cost of 200-600W switching power supplies and simplify the circuit structure.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A flyback switching power supply control circuit, comprising

[0007] PFC circuit;

[0008] The primary side AC filter and rectifier circuit is connected in series with the PFC circuit;

[0009] Secondary side filter rectifier circuit;

[0010] and a common-mode inductor TF1, the common-mode inductor TF1 is connected to the secondary-side filter and rectifier circuit;

[0011] Its characteristics are:

[0012] The power supply further comprises at least two transformers and an RCD absorption circuit respectively connected to each transformer. The input ends of the transformers and the RCD absorption circuits are connected to the PFC circuit, the RCD absorption circuits are connected in series, and the output ends of the transformers are connected to the secondary-side filter and rectifier circuit. The above design not only greatly reduces the heat generation of a single transformer, making heat treatment easier, but also solves the problems of high transformer leakage inductance and difficult-to-solve MOS tube voltage stress in high-power flyback circuits. At the same time, it can reduce the manufacturing cost of a 200-600W switching power supply and simplify the circuit structure.

[0013] Furthermore, it also includes an RCD peak absorption circuit, which is connected in parallel with the series RCD absorption circuit, the input end of the RCD peak absorption circuit is connected to the PFC circuit, and the output end of the RCD peak absorption circuit is connected to the transformer and the RCD absorption circuit.

[0014] Furthermore, the RCD peak absorption circuit includes a capacitor C12, a resistor R17, a resistor R18, and high-voltage diodes D8 and D9 connected in parallel in the same direction. After the capacitor C12, the resistor R17 and the resistor R18 are connected in parallel, they are connected in series with the parallel high-voltage diodes D8 and D9.

[0015] Furthermore, it also includes a field effect circuit, which is connected in series with the parallel RCD peak absorption circuit, the transformer and the RCD absorption circuit.

[0016] Furthermore, the field-effect circuit includes a field-effect transistor (FET) Q2. The drain of FET Q2 is connected in parallel to a series resistor R27 and a capacitor C20. The source of FET Q2 is connected to ground GND via parallel resistors R30, R31, R32, and R33. Resistor R30 is connected in series with capacitor C22. The gate of FET Q2 is connected in series with a parallel inductor L3 and a resistor R29. Resistor R29 is connected to the source of FET Q2. Inductor L3 is connected in series with chip U3 via resistor R26. FET Q2 is a MOS transistor.

[0017] Furthermore, the transformer includes a first transformer T1 and a second transformer T3, the RCD absorption circuit includes a first RCD absorption circuit and a second RCD absorption circuit, the first transformer T1 is connected to the first RCD absorption circuit, and the second transformer T3 is connected to the second RCD absorption circuit.

[0018] Furthermore, the first RCD absorption circuit includes a capacitor C3, a resistor R5, a resistor R6 and a high-voltage diode D4. The capacitor C3, the resistor R5 and the resistor R6 are connected in parallel and then connected in series with the high-voltage diode D4.

[0019] Furthermore, the second RCD absorption circuit includes a capacitor C11, a resistor R11, a resistor R12 and a high-voltage diode D6. The capacitor C11, the resistor R11 and the resistor R12 are connected in parallel and then connected in series with the high-voltage diode D6.

[0020] Furthermore, the secondary filter and rectifier circuit includes a first secondary filter and rectifier circuit and a second secondary filter and rectifier circuit. The first transformer T1 and the second transformer T3 are connected to the common mode inductor TF1 via the first secondary filter and rectifier circuit and the second secondary filter and rectifier circuit respectively.

[0021] Furthermore, an auxiliary power supply circuit is included, and the auxiliary power supply circuit is connected to the second transformer T3.

[0022] The utility model has the following beneficial effects due to the adoption of the above technical solution:

[0023] The utility model can not only greatly reduce the heat generation of a single transformer, making heat treatment easier, but also solve the problems of high leakage inductance of the transformer in a high-power flyback circuit and difficult-to-solve voltage stress of the MOS tube, while reducing the manufacturing cost of a 200-600W switching power supply and making the circuit structure simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings:

[0025] Figure 1 The utility model is a circuit diagram of a flyback switching power supply control circuit.

[0026] In the figure: 1-PFC circuit; 2-primary side AC filter and rectifier circuit; 3-first RCD absorption circuit; 4-second RCD absorption circuit; 5-RCD spike absorption circuit; 6-field effect circuit; 7-first secondary side filter and rectifier circuit; 8-second secondary side filter and rectifier circuit; 9-auxiliary power supply circuit. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] In order to help those skilled in the art better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0029] It should be noted that the terms "first," "second," and so on in the specification and claims of this utility model and the aforementioned drawings are used to distinguish similar items and are not necessarily used to describe a specific order or precedence. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0030] like Figure 1 As shown in the figure, a flyback switching power supply control circuit of the present invention includes a PFC circuit 1, a primary-side AC filter and rectifier circuit 2, a secondary-side filter and rectifier circuit and a common-mode inductor TF1.

[0031] The primary side AC filter and rectifier circuit 2 is connected in series with the PFC circuit 1. The PFC circuit 1 includes a PFC chip.

[0032] The switching power supply control circuit also includes at least two transformers and an RCD absorption circuit connected to each transformer. The input ends of the transformers and the RCD absorption circuits are connected to the PFC circuit 1, and the RCD absorption circuits are connected in series. The output ends of the transformers are connected to the secondary-side filter and rectifier circuit. Through this design, not only can the heat generation of a single transformer be greatly reduced, making heat treatment easier, but it also solves the problems of high transformer leakage inductance and difficult-to-solve MOS tube voltage stress in high-power flyback circuits. At the same time, it can reduce the manufacturing cost of 200-600W switching power supplies and simplify the circuit structure.

[0033] The utility model takes two transformers and two RCD absorption circuits as an example, the transformer includes a first transformer T1 and a second transformer T3, the RCD absorption circuit includes a first RCD absorption circuit 3 and a second RCD absorption circuit 4, the first transformer T1 is connected to the first RCD absorption circuit 3, and the second transformer T3 is connected to the second RCD absorption circuit 4.

[0034] The first RCD absorption circuit 3 includes a capacitor C3, a resistor R5, a resistor R6 and a high-voltage diode D4. The capacitor C3, the resistor R5 and the resistor R6 are connected in parallel and then connected in series with the high-voltage diode D4.

[0035] The second RCD absorption circuit 4 includes a capacitor C11 , a resistor R11 , a resistor R12 and a high-voltage diode D6 . The capacitor C11 , the resistor R11 and the resistor R12 are connected in parallel and then connected in series with the high-voltage diode D6 .

[0036] The switching power supply control circuit also includes an RCD peak absorption circuit 5, which is connected in parallel with the series RCD absorption circuit. The input end of the RCD peak absorption circuit 5 is connected to the PFC circuit 1, and the output end of the RCD peak absorption circuit 5 is connected to the transformer and the RCD absorption circuit.

[0037] The RCD peak absorption circuit 5 includes a capacitor C12, a resistor R17, a resistor R18, and high-voltage diodes D8 and D9 connected in parallel in the same direction. After the capacitor C12, the resistor R17 and the resistor R18 are connected in parallel, they are connected in series with the parallel high-voltage diodes D8 and D9.

[0038] The switching power supply control circuit further includes a field effect circuit 6 , which is connected in series with the parallel RCD peak absorption circuit 5 , the transformer, and the RCD absorption circuit.

[0039] Field-effect circuit 6 includes a field-effect transistor (FET) Q2. The drain of FET Q2 is connected in parallel to a series resistor R27 and capacitor C20. The source of FET Q2 is connected to ground GND via parallel resistors R30, R31, R32, and R33. Resistor R30 is connected in series with capacitor C22. The gate of FET Q2 is connected in series with an inductor L3 and a resistor R29 connected in parallel. Resistor R29 is connected to the source of FET Q2. Inductor L3 is connected in series with chip U3 via resistor R26. FET Q2 is preferably a MOS transistor. Chip U3 is preferably a FlyBuck chip.

[0040] The common-mode inductor TF1 is connected to the secondary-side filter and rectifier circuit.

[0041] The secondary filter and rectifier circuit includes a first secondary filter and rectifier circuit 7 and a second secondary filter and rectifier circuit 8. The first transformer T1 and the second transformer T3 are connected to the common mode inductor TF1 via the first secondary filter and rectifier circuit 7 and the second secondary filter and rectifier circuit 8 respectively.

[0042] The first secondary filter and rectifier circuit 7 includes capacitor C1, resistor R3, resistor R8, high-voltage diode D2, high-voltage diode D3, polarized capacitor C7, polarized capacitor C8, and polarized capacitor C9. Capacitor C1 is connected in series with resistor R3, then connected in parallel with high-voltage diodes D2 and D3, and then connected in parallel with resistor R8, polarized capacitor C7, polarized capacitor C8, and polarized capacitor C9, before being connected to common-mode inductor TF1.

[0043] The second secondary filter and rectifier circuit 8 includes a capacitor C10, a capacitor CY1, a resistor R9, a resistor R21, a high-voltage diode D5, a high-voltage diode D7, a polarized capacitor C13, a polarized capacitor C14, and a polarized capacitor C15. Capacitor C10 and resistor R9 are connected in series, then connected in parallel with the high-voltage diodes D5 and D7, which are then connected in parallel with resistor R21, polarized capacitor C13, polarized capacitor C14, and polarized capacitor C15, before being connected to a common-mode inductor TF1. One end of capacitor CY1 is connected to the second transformer T3, resistor R21, polarized capacitor C13, polarized capacitor C14, polarized capacitor C15, and common-mode inductor TF1, and the other end of capacitor CY1 is grounded.

[0044] The switching power supply control circuit also includes an auxiliary power supply circuit 9, which is connected to the second transformer T3. Auxiliary power supply circuit 9 includes a high-voltage diode D10, a high-voltage diode D11, a polarized capacitor C23, and a polarized capacitor C21. The high-voltage diode D10 and the polarized capacitor C23 are connected in series, and then connected in parallel with the series connection of the high-voltage diode D11 and the polarized capacitor C23. The polarized capacitors C23 and C21 are grounded.

[0045] The working principle of this utility model is as follows:

[0046] The mains electricity is rectified into a positive steamed bun wave after passing through F1-TF3-TF2-DB1-L1, and then passes through the PFC circuit to generate a stable DC voltage of about 600V on C4.

[0047] When the GET pin of the FlyBuck chip outputs a high voltage, Q2 is turned on, and current flows from the positive electrode of C4 through T1-T3-Q2-R31 / R32 / R33 to the negative electrode of C4. At this time, T1 and T3 are simultaneously excited to store energy.

[0048] The CS pin of the FlyBuck chip samples the excitation current through resistors R31 / R32 / R33, and turns off Q2 when the current reaches the limit of the CS pin.

[0049] Because the two transformers have the same inductance and their primary sides are connected in series, the current flowing through the transformers is the same. According to Q = 0.5*I*I*L, it can be seen that the energy stored in the two transformers is the same.

[0050] When Q2 is off, the secondary sides of both transformers release energy to the output. Since the outputs are connected in parallel and the transformers are identical, the demagnetization time for both transformers is the same, as shown by Vout*T=L*I. Therefore, there is no risk of excessive residual magnetism in one transformer, leading to unbalanced power output. When demagnetization is complete, the control chip turns Q2 back on, repeating the process.

[0051] When Q2 is turned off and the transformer is demagnetized, the spike voltage generated by the leakage inductance of the transformer primary side and the reflected voltage together will cause insufficient MOS stress. In the high-power flyback circuit, the spike caused by the leakage inductance is difficult to absorb. This dual-transformer solution adds an RCD absorption circuit to the primary side of each transformer. Since the primary sides are connected in series, the reflected voltage is equivalent to half of the single-transformer solution, and the power consumption and resistance loss of the absorption circuit can be reduced. Finally, a set of dual-transformer total RCD spike absorption circuits is added to solve the voltage stress of the MOS tube.

[0052] The double transformers share the total power in half, and the heat is also shared between the two transformers, so the heat treatment is simpler than that of a single transformer.

[0053] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements, or modifications based on the present invention to achieve substantially the same technical effects are included within the scope of protection of the present invention.

Claims

1. A flyback switching power supply control circuit, comprising PFC circuit; A primary AC filter and rectifier circuit, wherein the primary AC filter and rectifier circuit is connected in series with the PFC circuit; Secondary side filter rectifier circuit; and a common-mode inductor TF1, wherein the common-mode inductor TF1 is connected to the secondary-side filtering and rectifying circuit; Its characteristics are: It also includes at least two transformers and an RCD absorption circuit respectively connected to each of the transformers, the input ends of the transformers and the RCD absorption circuits are connected to the PFC circuit, the RCD absorption circuits are connected in series with each other, and the output end of the transformer is connected to the secondary side filter rectifier circuit.

2. The flyback switching power supply control circuit according to claim 1, wherein: It also includes an RCD peak absorption circuit, which is connected in parallel with the series RCD absorption circuit, the input end of the RCD peak absorption circuit is connected to the PFC circuit, and the output end of the RCD peak absorption circuit is connected to the transformer and the RCD absorption circuit.

3. The flyback switching power supply control circuit according to claim 2, wherein: The RCD peak absorption circuit includes a capacitor C12, a resistor R17, a resistor R18, and a high-voltage diode D8 and a high-voltage diode D9 connected in parallel in the same direction. After the capacitor C12, the resistor R17 and the resistor R18 are connected in parallel, they are connected in series with the high-voltage diode D8 and the high-voltage diode D9 connected in parallel.

4. The flyback switching power supply control circuit according to claim 2, wherein: It also includes a field effect circuit, which is connected in series with the RCD peak absorption circuit, the transformer and the RCD absorption circuit connected in parallel.

5. The flyback switching power supply control circuit according to claim 4, characterized in that: The field effect circuit includes a field effect transistor Q2, the drain of the field effect transistor Q2 is connected in parallel with a resistor R27 and a capacitor C20 connected in series, the source of the field effect transistor Q2 is connected to the ground line GND through parallel resistors R30, R31, R32 and R33, the resistor R30 is connected in series with a capacitor C22, the gate of the field effect transistor Q2 is connected in series with an inductor L3 and a resistor R29 connected in parallel, the resistor R29 is connected to the source of the field effect transistor Q2, and the inductor L3 is connected in series with the chip U3 through a resistor R26.

6. A flyback switching power supply control circuit according to any one of claims 1 to 5, characterized in that: The transformer includes a first transformer T1 and a second transformer T3 , and the RCD absorption circuit includes a first RCD absorption circuit and a second RCD absorption circuit. The first transformer T1 is connected to the first RCD absorption circuit, and the second transformer T3 is connected to the second RCD absorption circuit.

7. The flyback switching power supply control circuit according to claim 6, characterized in that: The first RCD absorption circuit includes a capacitor C3, a resistor R5, a resistor R6 and a high-voltage diode D4. The capacitor C3, the resistor R5 and the resistor R6 are connected in parallel and then connected in series with the high-voltage diode D4.

8. The flyback switching power supply control circuit according to claim 6, wherein: The second RCD absorption circuit includes a capacitor C11, a resistor R11, a resistor R12 and a high-voltage diode D6. The capacitor C11, the resistor R11 and the resistor R12 are connected in parallel and then connected in series with the high-voltage diode D6.

9. The flyback switching power supply control circuit according to claim 6, characterized in that: The secondary side filter and rectifier circuit includes a first secondary side filter and rectifier circuit and a second secondary side filter and rectifier circuit. The first transformer T1 and the second transformer T3 are connected to the common mode inductor TF1 via the first secondary side filter and rectifier circuit and the second secondary side filter and rectifier circuit respectively.

10. The flyback switching power supply control circuit according to claim 6, characterized in that: It also includes an auxiliary power supply circuit, which is connected to the second transformer T3.

Images