Analysis of the Parasitic Capacitance of MOSFET and Deadtime in High-Frequency ZVS Class-D Converters

This paper mainly analyzes the influence of the variation in the parasitic output capacitance (Coss) of MOSFET on the soft switching range of high-power and high-frequency full-bridge Class-D converters. Adjusting the input voltage is one of the important methods to regulate the output power of full-bridge Class-D converters. However, when the input voltage varies, the Coss of the MOSFET also changes. If the dead time cannot be adjusted instantly and properly, the converter risks losing zero-voltage switching (ZVS). This study examines the association between the load, switching frequency, and Coss, which affect the ZVS range of the converter. A theoretical calculation method for the dead time that ensures ZVS has been deduced and a 5kW/4MHz full-bridge Class-D converter prototype has been developed. Experimental results have verified the correctness of the estimated ZVS range.