A flyback synchronous rectification circuit

Abstract

The utility model discloses a flyback synchronous rectifier circuit, including a transformer, a switch tube, a triode and a diode; the first end of the primary side of the transformer serves as the first end of the input end of the rectifier circuit, the second end of the primary side of the transformer is connected to the drain of the switch tube Q1, and the source of the switch tube Q1 serves as the second end of the input end of the rectifier circuit; the drain of the switch tube Q5 is connected to the second end of the secondary side winding of the transformer T1, the source of the switch tube Q5 serves as the second end of the output end of the rectifier circuit, and the first end of the secondary side of the transformer serves as the first end of the output end of the rectifier circuit; the first end of the primary side of the transformer and the second end of the secondary side are the same-name ends. The utility model controls the peripheral circuit elements by converting the same-name ends of the transformer winding during the working process of the flyback power supply, and can realize the conduction and shutdown of the secondary side switch tube, avoiding the loss caused by the output rectifier diode in the traditional technology, reducing the conduction loss, and improving the power supply efficiency.

Description

Technical Field

[0001] The utility model belongs to the technical field of switch power supplies, and in particular relates to a flyback synchronous rectification circuit. Background Art

[0002] Switching power supplies are widely used to replace traditional linear power supplies due to their high efficiency and small size. Improving the power density of switching power supplies and making them smaller and lighter is a goal that people are constantly striving to achieve. To improve power density, to a certain extent, it is necessary to improve conversion efficiency. An effective way to improve the efficiency of power modules is to use synchronous rectification technology, that is, to replace the traditional diode rectification method with field effect transistors. Field effect transistors need to be driven by driving signals, so a driving circuit needs to be added.

[0003] However, the existing technologies mostly adopt the driving mode of integrated driver chip, and the chip needs a special auxiliary power supply circuit, which increases the number of components, increases the occupied space of the circuit board, increases the cost, and is not easy to integrate. Utility Model Content

[0004] In order to solve the above technical problems, the utility model provides a flyback synchronous rectification circuit.

[0005] The technical solution provided by the utility model is as follows:

[0006] A flyback synchronous rectifier circuit includes a transformer T1, a switch tube Q1, a transistor Q2, a transistor Q3, a transistor Q4, a switch tube Q5 and a diode D4; the first end of the primary side of the transformer T1 serves as the first end of the input end of the rectifier circuit, the second end of the primary side of the transformer T1 is connected to the drain of the switch tube Q1, and the source of the switch tube Q1 serves as the second end of the input end of the rectifier circuit;

[0007] The base of the transistor Q2 is connected to the second end of the secondary side of the transformer T1 through the diode D4, the collector of the transistor Q2 is connected to the base of the transistor Q3 and the base of the transistor Q4 respectively, and the emitter of the transistor Q2 and the collector of the transistor Q3 are connected to each other and grounded;

[0008] The emitter of the transistor Q3 is connected to the emitter of the transistor Q4 and the gate of the switch tube Q5 respectively, and the collector of the transistor Q4, the base of the transistor Q2 and the collector of the transistor Q2 are connected to each other and to the first end of the secondary side of the transformer T1;

[0009] The drain of the switch tube Q5 is connected to the second end of the secondary side winding of the transformer T1, the source of the switch tube Q5 serves as the second end of the output end of the rectifier circuit, and the first end of the secondary side of the transformer T1 serves as the first end of the output end of the rectifier circuit; the first end of the primary side of the transformer T1 and the second end of the secondary side are the same end.

[0010] Furthermore, an input filter capacitor C1 is provided at the input end of the rectifier circuit, the positive electrode of the input filter capacitor C1 is connected to the first end of the primary side of the transformer T1, and the negative electrode of the input filter capacitor C1 is connected to the source of the switch tube Q1.

[0011] Furthermore, an LC filter circuit is also provided at the output end of the rectifier circuit.

[0012] Furthermore, an output filter capacitor C2 is connected in parallel between the source of the switch tube Q5 and the first end of the secondary winding of the transformer T1.

[0013] Furthermore, a plurality of resistors are provided on the connection circuit between the collector of the transistor Q4, the base of the transistor Q2, the collector of the transistor Q2 and the first end of the secondary side of the transformer T1.

[0014] Beneficial effects of the utility model:

[0015] The flyback synchronous rectification circuit provided by the utility model can enable the power supply to supply power to the driving circuit with almost no additional loss. The flyback power supply controls the peripheral circuit elements by converting the same-name ends of the transformer winding during operation, thereby realizing the conduction and shutdown of the secondary side switch tube, avoiding the loss caused by the output rectifier diode in the traditional technology, reducing the conduction loss, and improving the power supply efficiency. In addition, the circuit structure of the utility model is simple and ingenious, and the required components are relatively few, so it is easy to integrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation to the present invention.

[0017] Figure 1 This is a schematic diagram of a flyback synchronous rectification circuit provided by an embodiment of the utility model. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiment of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the utility model.

[0019] like Figure 1As shown, this embodiment provides a flyback synchronous rectification circuit, which includes a transformer T1, a switch tube Q1, an input filter capacitor C1, an output filter capacitor C2, an inductor L1, an output filter capacitor C3, a switch tube Q5, a transistor Q2, a transistor Q3, a transistor Q4, a diode D4, and resistors R1, R2, and R3.

[0020] Among them, the positive electrode of the input filter capacitor C1 is connected to the first end of the primary side of the transformer T1, the negative electrode of the input filter capacitor C1 is connected to the source of the switch tube Q1, and the second end of the primary side of the transformer T1 is connected to the drain of the switch tube Q1. The base of the transistor Q2 is respectively connected to the anode of the diode D4 and the first end of the resistor R1, and the collector of the transistor Q2 is respectively connected to the base of the transistor Q3, the base of Q4 and the first end of the resistor R2. The collector of the transistor Q4 is connected to the first end of the resistor R3, and the emitter of the transistor Q4 is respectively connected to the emitter of the transistor Q3 and the gate of the switch tube Q5. The drain of the switch tube Q5 is respectively connected to the second end of the secondary side winding of the transformer T1 and the anode of the diode D4, and the source of the switch tube Q5 is electrically connected to the first output end of the flyback synchronous rectification circuit. The second end of the resistor R1, the second end of the resistor R2 and the first end of the resistor R3 are connected to each other, and the first end of the secondary winding of the transformer T1, the second end of the resistor R3 and the second output end of the flyback synchronous rectification circuit are connected to each other. The first end of the primary side of the transformer T1 and the second end of the secondary side of the transformer T1 are the same end.

[0021] The output end of the flyback synchronous rectification circuit is also provided with a filter circuit composed of an inductor L1 and an output filter capacitor C3, and the source of the switch tube Q5 and the first end of the secondary winding of the transformer T1 are also connected in parallel with an output filter capacitor C2.

[0022] The working principle of the flyback synchronous rectification circuit is as follows:

[0023] In the first time period, when the switch tube Q1 is turned on, the induced voltage of the primary winding of the transformer T1 is 1 (first end) positive and 2 (second end) negative, and the primary side of the transformer stores energy. At this time, due to the relationship between the same-name terminals, the voltage of the secondary winding of the transformer T1 is 1 (first end) negative and 2 (second end) positive, the transistor Q2 is cut off, Q4 is cut off, Q3 is turned on, and the switch tube Q5 is not turned on; in the second time period, when the switch tube Q1 is turned off, the induced voltage of the primary side of the transformer is 2 positive and 1 negative, and due to the relationship between the same-name terminals, the voltage of the secondary winding of the transformer is 1 positive and 2 negative, the base voltage of the transistor Q2 is clamped by the diode D4 to 0.7V, the transistor Q2 is turned on, the transistor Q4 is turned on, and Q3 is turned off. At this time, the gate voltage of the switch tube Q5 is the output voltage minus 0.7V, and the switch tube Q5 is turned on.

[0024] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Under the idea of ​​the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A flyback synchronous rectification circuit, characterized in that: It includes a transformer T1, a switch tube Q1, a triode Q2, a triode Q3, a triode Q4, a switch tube Q5 and a diode D4; the first end of the primary side of the transformer T1 serves as the first end of the input end of the rectifier circuit, the second end of the primary side of the transformer T1 is connected to the drain of the switch tube Q1, and the source of the switch tube Q1 serves as the second end of the input end of the rectifier circuit; The base of the transistor Q2 is connected to the second end of the secondary side of the transformer T1 through the diode D4, the collector of the transistor Q2 is connected to the base of the transistor Q3 and the base of the transistor Q4 respectively, and the emitter of the transistor Q2 and the collector of the transistor Q3 are connected to each other and grounded; The emitter of the transistor Q3 is connected to the emitter of the transistor Q4 and the gate of the switch tube Q5 respectively, and the collector of the transistor Q4, the base of the transistor Q2 and the collector of the transistor Q2 are connected to each other and to the first end of the secondary side of the transformer T1; The drain of the switch tube Q5 is connected to the second end of the secondary side winding of the transformer T1, the source of the switch tube Q5 serves as the second end of the output end of the rectifier circuit, and the first end of the secondary side of the transformer T1 serves as the first end of the output end of the rectifier circuit; the first end of the primary side of the transformer T1 and the second end of the secondary side are the same end.

2. A flyback synchronous rectification circuit as claimed in claim 1, characterized in that: An input filter capacitor C1 is also provided at the input end of the rectifier circuit. The positive electrode of the input filter capacitor C1 is connected to the first end of the primary side of the transformer T1, and the negative electrode of the input filter capacitor C1 is connected to the source of the switch tube Q1.

3. A flyback synchronous rectification circuit as claimed in claim 1, characterized in that: The output end of the rectifier circuit is also provided with an LC filter circuit.

4. A flyback synchronous rectification circuit as claimed in claim 1, characterized in that: An output filter capacitor C2 is also connected in parallel between the source of the switch tube Q5 and the first end of the secondary winding of the transformer T1.

5. A flyback synchronous rectification circuit as claimed in claim 1, characterized in that: A plurality of resistors are arranged on the connection circuit between the collector of the transistor Q4, the base of the transistor Q2, the collector of the transistor Q2 and the first end of the secondary side of the transformer T1.

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