Synchronous rectification control circuit

Abstract

The invention discloses a synchronous rectification control circuit, which is applied to an active clamping flyback converter and is used for transmitting a falling edge of a clamping switch tube driving signal to a secondary side and converting the falling edge into an enabling control signal to control the turn-off of a synchronous rectification tube. As a specific implementation mode, the synchronous rectification control circuit further comprises a switching tube Q3, an isolation transformer T2, a resistor R2, a capacitor C3 and a resistor R3 on the basis of the prior art, wherein one end of the resistor R2 inputs a working voltage, the other end of the resistor R2 is connected with one end of the switching tube Q3 and one end of the capacitor C3, the control end of the switching tube Q3 inputs a signal synchronous with a clamping tube driving signal, the other end of the switching tube Q3 is simultaneously connected with one end of the resistor R3, one end of the primary side of the isolation transformer T2 and the primary side ground, the other end of the capacitor C3 is simultaneously connected with the other end of the resistor R3 and the other end of the primary side of the isolation transformer T2, one end of the secondary side of the isolation transformer T2 is connected with an enable signal pin of a synchronous rectification control chip, and the dotted terminal of the secondary side of the isolation transformer T2 is connected with the secondary side ground. According to the invention, the synchronous rectifier tube can be switched off in advance before the main tube is switched on.

Description

technical field

[0001] The invention relates to the field of switching converters, in particular to the synchronous rectification control of active clamp flyback switching converters. Background technique

[0002] Active clamp flyback (Active Clamp Flyback, ACF) converter is a kind of flyback converter, which has a main switch tube that can realize zero voltage turn-on (ZVS), leakage inductance can be absorbed without loss, and the voltage spike of the main switch tube is small , high efficiency and other advantages, the application is more and more extensive. The circuit schematic diagram of the existing conventional active clamp flyback converter is as follows: figure 1 , figure 1 Among them, Q1 is the main switching tube (hereinafter referred to as the supervisor), Q2 is the clamping switching tube (hereinafter referred to as the clamping tube), Cc is the clamping capacitor; Ds1 is the body diode of the main switching tube Q1, and Ds2 is the clamping switching tube bod...

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