Synchronous rectification switching power supply circuit, secondary side control circuit and method thereof

Abstract

Disclosed is a synchronous rectification switching power supply circuit and a control method thereof, which prevent false turn-on caused by voltage oscillation by detecting the conversion rate of the drain-source voltage of a synchronous rectification switch. The circuit includes a synchronous rectification switch coupled to the secondary side of the energy storage element and a secondary side control circuit. The secondary side control circuit includes a turn-on control circuit, a slew rate detection circuit and a gate driver. The turn-on control circuit compares the drain-source detection voltage of the synchronous rectification switch with the turn-on threshold to generate a turn-on control signal. The slew rate detection circuit outputs a mode signal representing the detection result. When the mode signal is at a low level, it indicates the fast opening mode, and the gate driver charges the gate voltage of the synchronous rectification switch after the first delay when the control signal is enabled; when the mode signal is at a high level, it indicates the slow opening mode, and the gate driver The pole driver charges the gate voltage of the synchronous rectification switch after the second time delay when the turn-on control signal is effective, wherein the second time delay is greater than the first time delay.

Description

technical field [0001] The present invention mainly relates to an electronic circuit, especially but not exclusively to a switching power supply circuit for synchronous rectification and a control method thereof. Background technique [0002] The secondary-side synchronous rectification scheme usually refers to receiving the input voltage on the primary side of the transformer, and using a controllable switch tube instead of a diode on the secondary side of the transformer to convert the input voltage into the required output voltage. It is widely used because of its high conversion efficiency. [0003] In the secondary-side synchronous rectification solution, the synchronous rectification switch is usually turned on and off according to the drain-source voltage of the synchronous rectification switch. At the same time, in order to avoid false turn-on of the synchronous rectification switch caused by oscillation, the slope of the drain-source voltage of the synchronous rect...

AI Technical Summary

Problems solved by technology

However, with the increase of the switching frequency of the switching power supply, the slope of the drain-source voltage of the synchronous rectification switch during oscillation is getting closer and closer to the slope during normal turn-on, and the existing slope detection method can no longer be accurately controlled. The conduction of the synchronous rectification switch

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