A Synchronous Rectification Method with Switching Delay for CLLC Converters to Achieve Secondary-side ZVS

The CLLC resonant converters have huge potential in battery charging applications. In order to reduce the conduction loss, synchronous rectification (SR) technique is widely applied. However, conventional SR method ignores the dead time resonance and thus leads to hard turn-on of switches in secondary side, which is especially harmful in light load conditions. In this paper, a novel SR method with switching delay for CLLC converters is proposed, and appropriate switching delay time is derived. The proposed method can realize soft switching in secondary side while maintaining the benefits of SR. Experiments are adjusted under different load conditions to validate the zero-voltage switching (ZVS) achieved by the proposed method. The results also show the efficiency improvement of proposed method over both conventional SR and uncontrolled rectification.