Comparison Between Forced CCM and DCM on Low Load Efficiency of a SiC Based DC/DC Converter

The internal body diode of Silicon Carbide (SiC)-MOSFETs shows a small reverse recovery charge but a large forward voltage drop. In a converter that operates in continuous-conduction-mode (CCM) with synchronous rectification, the losses due to this forward voltage drop are neglectable. To maintain high efficiency under light-load in discontinuous-conduction mode (DCM) either an external SiC Schottky- Barrier-Diode (SBD) in parallel to the body diode or small phase currents are required. Both result in low rectifying losses. In this work an option to operate a SBD-less SiC-based half bridge buck/boost converter in light-load but also with high efficiency is examined. It is tested in a high power density (7.5 kW/kg) buck/boost converter.