A novel variable frequency soft switching method for Flyback converter with synchronous rectifier

This paper proposes a variable frequency zero-voltage-switching (ZVS) control method for Flyback converter with synchronous rectifier. A lossless snubber capacitor is paralleled to the drain and source of primary switch to absorb the leakage inductance energy. The conventional passive clamp circuit with RCD is omitted, and no auxiliary switch or winding is needed. Synchronous rectifier is turned on additionally for a short time before primary switch is on. The negative secondary current transferred to primary side is used to discharge the auxiliary capacitor and achieve ZVS operation. Experimental results from a 16 V/4 A prototype circuit are provided to demonstrate the converter performance. Both Soft-switching and high efficiency are achieved in the entire input voltage range at both full load and light load conditions.