Soft switching control circuit and control method of flyback converter

By introducing a negative excitation module into the flyback converter, the negative excitation current is controlled to release the junction capacitance charge of the switching transistor, achieving zero-voltage turn-on. This solves the problem of high hard-turn-on losses of the switching transistor under light or medium load conditions in the flyback converter, and improves transmission efficiency and reliability.

CN115776238BActive Publication Date: 2026-07-17JOULWATT TECH INC LTD
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Patents(China)
Current Assignee / Owner
JOULWATT TECH INC LTD
Filing Date
2022-11-29
Publication Date
2026-07-17

AI Technical Summary

Technical Problem

The hard turn-on of the switching transistors in flyback converters under light or medium load conditions leads to significant turn-on losses, especially in intermittent conduction mode.

Method used

In a flyback converter, a negative excitation module is introduced and connected to the transformer winding. By controlling the negative excitation module to turn on after the switching transistor is turned off, a negative excitation current is generated to release the junction capacitance charge, so that the switching transistor can turn on at zero voltage, thus achieving soft switching.

Benefits of technology

It reduces the turn-on loss of the switching transistors, improves the transmission efficiency of the flyback converter under light or medium load, and enhances the reliability of the system.

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    Figure CN115776238B_ABST
Patent Text Reader

Abstract

The application discloses a soft switching control circuit and a control method of a flyback converter. The soft switching control circuit of the flyback converter comprises a negative excitation module connected with a winding of a transformer, the negative excitation module forms a current loop with the winding when turned on, a negative excitation current is generated on the transformer, and the junction capacitance charge of a first switch tube is released after the negative excitation module is turned off; and a switch control module connected with the first switch tube, a second switch tube and the negative excitation module, outputs a switch control signal to control the turn-on and turn-off of the first switch tube and the second switch tube, and outputs a negative excitation signal to control the turn-on or turn-off of the negative excitation module. The scheme of the application can generate a negative excitation current in the transformer when the first switch tube and the second switch tube of the flyback converter are both in the turn-off state, release the junction capacitance charge of the first switch tube, make the source-drain voltage drop to zero, realize the soft switching control of the first switch tube, reduce the switching loss and improve the transmission efficiency.
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