A 6.78-MHz Class E2 Converter with the Flexible DC-DC Voltage Ratio

High frequency DC-DC converters working at megahertz (MHz) are promising candidates for making compact, highly efficient converters with galvanic isolation. However, it is challenging when requiring the system design of different final loads and voltage ratios. In this paper, a design method is proposed to adjust the voltage ratio of a Class E² DC-DC converter by only changing the capacitors. the experimental 6.78 MHz Class E² converter system works with the overall efficiency of 80.1%, 83.1% and 83.8% and the DC-DC voltage ratio ranging from 2 to 5. The inductors of the system remain unchanged under different voltage ratios. In addition, a expansion approach is proposed to further increase the system voltage ratio when the input resistance of the coupling coils is already high to the PA.