Re-analysis on ZVS Condition for LLC Converter

Abstract

LLC convertor is widely used because of ZVS operation of primary switches and ZCS operation of secondary switches. These features make it suitable for high fs design to cater for the miniaturization trend of switching mode power supply (SMPS). ZVS operation of the primary switches is critical for high fs design to achieve high efficiency. Traditional analysis of the ZVS condition for LLC converter is not accurate enough for high fs design. This paper gives a detail analysis on the operation modes during the dead time interval. An accurate ZVS condition is derived based on the analysis. The verification of the theoretical analysis has been carried out with simulation and a half-bridge(HB) LLC prototype.