Analysis on Synchronous Rectifier Control to Improve Regulation Capability of High-Frequency LLC Resonant Converter

A new synchronous rectifier (SR) control method is proposed to improve the light-load regulation capability of high-frequency LLC resonant converter. The proposed control method applies the extended SR turn-on time, which results in the negative current flowing through SRs, and the light-load regulation of the LLC resonant converter can be achieved by the negative current. The design guideline of the extended SR turn-on time is presented based on the precise analysis and the equivalent circuit modeling of the LLC resonant converter. In addition, the switching loss and gate driving loss can be reduced because the output voltage can be regulated at low switching frequency. The validity of a proposed control method is confirmed by the experimental results of a prototype converter with 330-380 VDC input and 750 W (12 V/62.5 A) output.