Synchronous rectification circuit with flyback output

Abstract

The utility model discloses a flyback output synchronous rectification circuit, which belongs to the technical field of power electronics, and relates to a synchronous rectification driving circuit, the circuit comprises an MOS (Metal Oxide Semiconductor) tube, an absorption circuit and a driving circuit, the drain electrode of the MOS tube is connected with the dotted terminal of a secondary winding, and the source electrode of the MOS tube is grounded; the filter circuit is formed by connecting a fifth resistor and a second capacitor in series and is connected between the drain electrode and the source electrode of the MOS tube in parallel. The driving circuit comprises first to fourth resistors, first to fourth triodes and first to third diodes. Compared with the prior art, the circuit is only composed of basic components, the use of a chip circuit is avoided, the external dependence degree and the production cost of a product are reduced, the whole circuit structure is simple, the applicability is high, and synchronous rectification work of various voltages can be reliably completed.

Description

TECHNICAL FIELD

[0001] The utility model belongs to power electronics technical field, especially relate to a synchronous rectification circuit of flyback output. BACKGROUND

[0002] Synchronous rectification drive circuit is an important component of DC power supply, in the prior art, when rectifying the output of flyback topology DC power supply, technicians usually use diode to rectify, which has problems such as large loss and low efficiency. Some technicians also use existing mature chips to rectify and drive, in the above-mentioned synchronous rectification scheme, self-driving is only applicable to power supply with DC output of about 5V, in addition, due to the limited voltage resistance of the chip, it is not suitable for synchronous rectification of the secondary winding voltage higher than the voltage resistance of the chip.

[0003] In order to further improve the reliability of the circuit and reduce the cost, meet the military standard and localization substitution, a synchronous rectification circuit of flyback output is urgently needed to solve the above technical problems. UTILITY MODEL CONTENTS

[0004] In view of the above technical problems, the utility model provides a synchronous rectification circuit of flyback output, which solves the above problems by the following technical means:

[0005] A synchronous rectification circuit of flyback output, characterized by comprising a MOS tube, an absorption circuit and a drive circuit, wherein: the drain of the MOS tube is connected to the same end of the secondary winding, and the source of the MOS tube is grounded; The filter circuit is composed of a fifth resistor and a second capacitor in series, and the filter circuit is connected in parallel between the drain and the source of the MOS tube; The drive circuit comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a first triode, a second triode, a third triode, a fourth triode, a first diode, a second diode and a third diode, wherein: the two ends of the first resistor are respectively connected to the source and the gate of the MOS tube; The +12V power supply is divided into three paths, the first path of the +12V power supply is connected to the collector of the third triode through the third resistor, the second path of the +12V power supply is connected to the collector of the first triode, and the third path of the +12V power supply is connected to the base of the first triode and the second triode through the fourth resistor, the emitter of the third triode is connected to the drain of the MOS tube through the second diode, the emitters of the first triode and the second triode are interconnected, the emitters of the first triode and the second triode are interconnected and connected to the gate of the MOS tube through the second resistor, the collector of the second triode is grounded, the bases of the third triode and the fourth triode are interconnected, and the emitter of the fourth triode is grounded through the third diode.

[0006] Preferably, it further comprises a filter circuit, and the filter circuit comprises a first capacitor, and the two ends of the first capacitor are respectively connected between the +12V power supply line and the ground.

[0007] The synchronous rectifier circuit with flyback output of this utility model has the following beneficial effects:

[0008] This circuit includes a MOSFET, an absorption circuit, and a driving circuit. The driving circuit can complete the circuit rectification work based on the self-driving switching of the MOSFET. This circuit only uses basic components to solve the technical problem of large voltage drop on existing diodes, which will generate large losses and reduce efficiency. It effectively avoids the use of chip circuits, reduces the product's external dependence and production costs. The overall circuit structure is simple, highly applicable, and can reliably complete the synchronous rectification of various voltages. Attached Figure Description

[0009] To more clearly illustrate the technical solution of this utility model, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of the overall circuit of this utility model. Detailed Implementation

[0011] In the description of this utility model, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0012] The present invention will now be described in detail with reference to the accompanying drawings.

[0013] like Figure 1As shown, the synchronous rectifier circuit with flyback output includes a MOSFET Q1, an absorption circuit, and a drive circuit. In the figure, the drain of MOSFET Q1 is connected to the same-name terminal of the secondary winding, and the source of MOSFET Q1 is grounded. The filter circuit consists of a fifth resistor R5 connected in series with a second capacitor C2, and the filter circuit is connected in parallel between the drain and source of MOSFET Q1. The drive circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first transistor VT1, a second transistor VT2, a third transistor VT3, a fourth transistor VT4, a first diode D1, a second diode D2, and a third diode D3. The two ends of the first resistor R1 are connected to the source and gate of MOSFET Q1, respectively. The +12V power supply is divided into three paths, with the first path of the +12V power supply... The collector of the third transistor VT3 is connected through the third resistor R3. The second path of the +12V power supply is connected to the collector of the first transistor VT1. The third path of the +12V power supply is connected to the bases of both the first transistor VT1 and the second transistor VT2 through the fourth resistor R4. The emitter of the third transistor VT3 is connected to the drain of the MOSFET Q1 through the second diode D2. The emitters of the first transistor VT1 and the second transistor VT2 are interconnected. After being interconnected, the emitters of the first transistor VT1 and the second transistor VT2 are connected to the gate of the MOSFET Q1 through the second resistor R2. The collector of the second transistor VT2 is grounded. The bases of the third transistor VT3 and the fourth transistor VT4 are interconnected. The emitter of the fourth transistor VT4 is grounded through the third diode D3.

[0014] Specifically, it also includes a filter circuit, which includes a first capacitor C1, with its two ends connected between the +12V power supply line and ground, respectively.

[0015] It should be noted that resistors R5 and C2 form an absorption circuit to absorb the drain-source spikes of Q1. C1 filters the 12V auxiliary power supply, and R1, R2, R3, R4, VT1, VT2, VT3, VT4, D1, D2, and D3 form a drive circuit to drive the gate of Q1.

[0016] In this example, the specific working principle of the circuit is as follows:

[0017] When the secondary winding is positive at the top and negative at the bottom, due to the body diode between the source and drain of Q1, the current flows from OUT+ through the load, then through the source of Q1 to the drain. At this time, the drain of Q1 is at a low level. Since VT4 is connected to the output ground through D3, the output ground voltage is higher than the drain of Q1. D2 and D3 have the same parameters, and VT3 and VT4 have the same parameters, so VT3 is turned on. After VT3 is turned on, the base of VT3 is at a low level, so VT4 is not turned on. The lower end of R4, i.e., the base of VT1 and VT2, is at a high level. At this time, VT1 is turned on, VT2 is not turned on, and the 12V voltage is input to the gate of Q1 through VT1 and R2, turning on Q1.

[0018] When the secondary winding is negative at the top and positive at the bottom, the drain of Q1, i.e., the cathode of D2, is at a high level relative to 12V and the base of VT3, so VT3 is not conducting. At this time, the base of VT4 is at a high level, so VT4 is conducting. The lower end of R4, i.e., the base of VT1 and VT2, is at a low level, so VT2 is conducting and VT1 is not conducting. The gate of Q1 discharges quickly to ground through R2 and VT2, thus achieving synchronous rectification.

[0019] It should be noted that the circuit includes a MOSFET, a snubber circuit, and a drive circuit. The drive circuit can complete the circuit rectification work based on the self-driven switching of the MOSFET. This circuit is composed of only basic components, which can solve the technical problem of large voltage drop on existing diodes, resulting in large losses and reduced efficiency. It effectively avoids the use of chip circuits, reduces the product's external dependence and production costs. The overall circuit structure is simple, highly applicable, and can reliably complete the synchronous rectification of various voltages.

[0020] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A synchronous rectification circuit for flyback output, characterized in that, Including MOS tube (Q1), absorption circuit and drive circuit, and filter circuit, wherein: The drain of the MOS tube (Q1) is connected to the same end of the secondary winding, and the source of the MOS tube (Q1) is grounded. The filter circuit is composed of a fifth resistor (R5) and a second capacitor (C2) in series, and the filter circuit is connected in parallel between the drain and the source of the MOS tube (Q1). The drive circuit includes a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth resistor (R4), a first transistor (VT1), a second transistor (VT2), a third transistor (VT3), a fourth transistor (VT4), a first diode (D1), a second diode (D2), and a third diode (D3), wherein: The two ends of the first resistor (R1) are respectively connected to the source and gate of the MOS tube (Q1). The +12V power supply is divided into three paths, the first path of the +12V power supply is connected to the collector of the third transistor (VT3) through the third resistor (R3), the second path of the +12V power supply is connected to the collector of the first transistor (VT1), and the third path of the +12V power supply is connected to the base of the first transistor (VT1) and the second transistor (VT2) through the fourth resistor (R4), the emitter of the third transistor (VT3) is connected to the drain of the MOS tube (Q1) through the second diode (D2), the emitters of the first transistor (VT1) and the second transistor (VT2) are interconnected, the emitter of the first transistor (VT1) and the emitter of the second transistor (VT2) are interconnected and connected to the gate of the MOS tube (Q1) through the second resistor (R2), the collector of the second transistor (VT2) is grounded, the bases of the third transistor (VT3) and the fourth transistor (VT4) are interconnected, and the emitter of the fourth transistor (VT4) is grounded through the third diode (D3).

2. The flyback output synchronous rectification circuit of claim 1, wherein, It also includes a filter circuit, which includes a first capacitor (C1), and the two ends of the first capacitor (C1) are respectively connected between the +12V power supply line and the ground.

Images