An ac-dc power supply and its synchronous rectifier control circuit

Abstract

The invention discloses an AC-DC power supply and a control circuit of a synchronous rectifier thereof, The control circuit of the synchronous rectifier comprises a primary side volt second integratorcircuit, an integrating comparator circuit, a current source regulating circuit, a minimum off time generating circuit and a logic circuit, wherein the primary side volt second integrator circuit, the integrating comparator circuit, the current source regulating circuit, the minimum off time generating circuit and the logic circuit are sequentially connected. The invention indirectly detects theAC-DC power load by using the magnitude of the integrated signal generated by the primary side voltage second integrator circuit, and a minimum turn-off time signal of different magnitudes is generated according to different loads, At light load or no load, the minimum turn-off time signal is large enough to shield the continuous mis-opening phenomenon of the synchronous rectify tube caused by resonance, and the problem that the continuous inductor current backflow phenomenon occur at light load due to the mis-opening phenomenon of the synchronous rectifier tube is solved, and the output can not be energized finally.

Description

technical field [0001] The invention relates to AC-DC switching power supply technology, in particular to an AC-DC power supply and a control circuit for a synchronous rectifier tube thereof. Background technique [0002] As switching power supplies have increasingly stringent requirements for efficiency, it has become an inevitable technical trend to use synchronous rectification MOS tubes to replace freewheeling diodes. [0003] However, when there is no communication between the synchronous rectification MOS tube and the main switch signal on the primary side, how to correctly turn on and off the synchronous rectification MOS tube has become a key technology; the turn-off technology is relatively simple and is very mature at present, and the difficulty lies in the turn-on technology. [0004] At present, the mainstream turn-on technology of synchronous rectifiers on the market is to detect whether the drain-source voltage Vds of synchronous rectifiers is less than a set t...

AI Technical Summary

Problems solved by technology

[0008] In view of the deficiencies of the prior art above, the purpose of the present invention is to provide a control circuit for an AC-DC power supply and its synchronous rectifier, which can solve the current problem of continuous inductive current at light loads caused by the false opening of the synchronous rectifier. The backflow phenomenon eventually leads to the problem that the output cannot be energized

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