Investigation of Peak Voltage Suppression Method at Startup in Isolated DC-DC Converter with Class Phi-2 Inverter

In this paper, we discuss the method of reducing peak voltage between drain and source, it is occurred during the start of the class Phi-2 inverter. The class Phi-2 inverter is resonance inverter circuit with only one switching device, it is able to operate at high frequency. During start of this circuit, 150% peak voltage is impressed on switching device in comparison with steady state, so increase of voltage stress is concerned. Especially, if we use the class Phi-2 inverter as DC-DC converter with ON/OFF control, this problem is more remarkable. In this study, we applied the soft-start method to switching device GaN-HFET (GaN-Hetero-junction Field Effect Transistor) and investigated reduction of peak voltage during start of the circuit. From simulation and experimental investigation, the peak voltage has been reduced by 75%, we confirmed the stress of the switching device is reduced by proposed soft-start method. Therefore, it is possible to operate under higher input voltage of class Phi-2 inverter even if low withstand voltage semiconductor is applied.