A Resonant 1:5 Cockcroft-Walton Converter Utilizing GaN FET Switches with N-Phase and Split-Phase Clocking

Recent demonstrations of merged inductor-capacitor (LC) switching converters have resulted in record power densities being achieved at high voltage conversion ratios. To do so, sophisticated switch control schemes may be required. This work demonstrates N-phase and Split-phase switching techniques applied to a resonant Cockcroft-Walton converter. For the same hardware, the lower resonant switching frequency of the N-phase scheme significantly improves light-load efficiency relative to the Split-phase scheme. However, the N-phase approach suffers reverse body diode turn-on at large voltage ripple contributing to the Split-phase scheme obtaining the highest power density. Converter performance combining both switching techniques is analyzed using a discrete 1:5 Cockcroft-Walton converter implemented using gallium nitride FETs, multi-layer ceramic chip (MLCC) capacitors, and a 68 nH inductor. The resulting converter achieves a peak efficiency of 94.9% and 94% for the N-phase and Split-phase schemes respectively with the N-phase scheme seeing a 30% reduction in losses at light-load. The converter achieves a maximum output power of 190W, resulting in a record power density of 483.3 kW/liter (7,920 W/inch
³
) and specific power of 243 kW/kg.