Optimisation of the Synchronous Rectifier in Phase Shift Full Bridge Converters for High-Frequency Applications

Efforts to minimise the size and material usage of power converters are reflected in efforts to increase the switching frequency. The problem is that semiconductor switching losses are proportional to the switching frequency, so it is necessary to find ways to keep efficiency high at higher switching frequencies. Gallium nitride (GaN) transistors have made it possible to improve the parameters of many topologies due to a better figure of merit (FOM). Thanks to GaN technology, it is possible to increase the soft switching range in the inverter of phase-shift full-bridge (PSFB) converter and thus reduce switching losses. This paper addresses the selection of semiconductor transistors for a synchronous rectifier (SR) operating at 500 kHz. Based on mathematical calculations and simulation results in the programme PLECS, the converter was designed and measured under laboratory conditions. The paper highlights the advantages and challenges of using GaN transistors in SRs, which, when properly applied, enable lower losses and thus higher efficiency at a switching frequency of 500 kHz.