A New Current-Driven Synchronous Rectifier for Series-Parallel Resonant ( LLC ) DC-DC Converter

A new synchronous rectifier (SR) driving method is proposed using primary current sensing in this paper. Because the magnetizing current of transformer is included in primary winding of transformer, it can’t be used to generate the driving signals of SRs directly. A current compensating winding in current transformer is used to cancel out the magnetizing current and generate suitable driving signals for SR. Therefore, one CT is used to generate two driving signals for two SRs in LLC converter with center tapped rectifier. This current driven method is simple and low cost for high output current DC-DC application. A 150W DC-DC prototype using LLC half bridge converter with proposed SR circuit is built up to verify the theoretical analysis.