Flyback synchronous rectification control circuit

Abstract

The invention relates to a flyback synchronous rectification control circuit, comprising a primary switching tube (Q1), a synchronous rectifier tube (Q2), a primary side of a main transformer (T1), a subsidiary side of the main transformer (T2), a synchronous rectifier module, a control circuit composed of a drive circuit (1), a delay circuit (2), a signal same-phase transmission circuit (3), a sharp pulse forming circuit (4) and a synchronous rectification forcibly turned-off circuit (5). When a power source operates in a continuous mode, the synchronous rectifier tube (Q2) can be forcibly turned off in advance through the control circuit, thus reverse current can not pass through the synchronous rectifier tube (Q2), thereby reducing the loss and the voltage stress of the synchronous rectifier tube (Q2), and improving the efficiency of the power source; and when the power source operates in a discontinuous mode or in a critical continuous mode, the control circuit is inoperative, and can not influence the normal operation of the circuit.

Description

technical field [0001] The invention relates to a switching power supply, in particular to a flyback synchronous rectification control circuit for the switching power supply to work in a continuous mode. Background technique [0002] With the development of technology, the conversion efficiency of the power supply is required to be higher and higher, and it has become a trend to replace the traditional diode rectification with synchronous rectification. Traditional synchronous rectification circuits such as figure 1 , its working principle is: use the forward voltage drop and reverse voltage drop generated by the current flowing through the rectifier tube (MOSFET) to control, when it is detected that the forward voltage drop across the rectifier tube reaches a certain set threshold At this point, the synchronous rectification circuit or control IC drives the rectifier to turn on; once the voltage drop at both ends drops to zero or there is a reverse voltage drop, the contro...

AI Technical Summary

Problems solved by technology

[0006] In order to solve the defects of large loss of synchronous rectification circuit components and low power supply efficiency and reliability in the prior art, the present invention provides a primary switching tube (Q1), a synchronous rectifying tube (Q2), the primary side of the main transformer (T1), and the main transformer The secondary side and synchronous rectification module of (T1) is characterized in that: it also includes drive circuit (1), delay circuit (2), signal in-phase transmission circuit (3), sharp pulse forming circuit (4) and synchronous rectification forced A control circuit composed of a shutdown circuit (5), the delay circuit (2) and the drive circuit (1) are connected in series, and the other end of the delay circuit (1) receives the PWM signal (U1) and the drive signal (DRV), The other end of the driving circuit (1) is connected to the gate of the primary switching tube (Q1), the signal in-phase transmission circuit (3), the sharp pulse forming circuit (4), the synchronous rectification forced shutdown circuit (5) and The gates of the synchronous rectifier (Q2) are connected sequentially; the synchronous rectifier module is respectively connected to the drain and source of the synchronous rectifier (Q2)

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