A Zero-Crossing Noise Filter for Driving Synchronous Rectifiers of LLC Resonant Converter

A new driving method for synchronous rectifier (SR) in LLC resonant converter is presented. By adding a zero-crossing noise filter (ZCNF) to the drain and source of the SR FET, the false-triggering of the SR can be effectively eliminated. Moreover, the resistor and the capacitor in the filter can be used as a compensator to solve the duty-cycle loss issue caused by the trace inductance of the MOSFET package. Only three passive components are needed in the proposed filter, which makes it reliable and easy to implement. Simulation and experimental results show that the ZCNF can significantly improve the reliability as well as the efficiency of the power circuit. A prototype of 400 V to 12 V 600-W half-bridge LLC resonant converter is built to verify the advantages of the ZCNF. An efficiency improvement of 0.8% is achieved by the ZCNF.