Variable Switching Frequency ON–OFF Control for Class E DC–DC Converter

The efficiency improvement of the on-off controlled Class E dc-dc converter operated at 20 MHz switching frequency is investigated in this paper. It is found that with the on-off control, the input power of the converter during the on mode increases with the increase of the input voltage, and it can be reduced by increasing the switching frequency. With this discovery, a variable switching frequency (VSF) on-off control is proposed, which slightly increases the switching frequency when the input voltage increases, maintaining the input power during the on mode slightly higher than the rated output power over the entire input voltage range, and thus highly improving the efficiency of Class E dc-dc converter at high input voltage. A prototype of 9-V-18-V input, 10-W Class E dc-dc converter has been fabricated and tested in the lab. The experimental results show that the proposed VSF on-off control improves the conversion efficiency of the Class E dc-dc converter by 4%-10% compared to the constant switching frequency on-off control.