Dual-Frequency On-Off Control for a 20 MHz Class E DC-DC Converter

The Class E dc-dc converter, operating with the switching frequency up to multi-megahertz, is usually regulated by the basic ON-OFF control. In this paper, it is found that in the basic ON-OFF control, the resonant inductor current of the Class E dc-dc converter will be increase with the rise of the input voltage, which will enhance the output capacity of the converter and also increase the ON-OFF modulation frequency. On one hand, the increased resonant current will lead to higher conduction loss in the inductor, and on the other hand, the increased ON-OFF frequency will produce higher ON-OFF transition loss, resulting in reduction of conversion efficiency. It is revealed that in the Class E dc-dc converter, increasing the switching frequency will weaken the output power capacity but help reduce the resonant inductor current. Since the output power capacity under high input voltage is far higher than the required output power, the conversion efficiency under high input voltage could be increased with a higher switching frequency. This paper proposes a dual frequency ON-OFF control to regulate the output voltage of the Class E dc-dc converter. Compared to the basic ON-OFF control, there are two optional switching frequencies in the proposed control scheme. The Class E dc-dc converter operates at either of these two switching frequencies according to the input voltage and the load condition. Under the high input voltage or light load, the higher switching frequency is adopted such that the ON-OFF transition loss and the conduction loss produced by the resonant inductor can be reduced. To verify the effectiveness of the proposed dual-frequency ON-OFF control, a 20 MHz, 10W Class E dc-dc converter was built in the lab. The experimental results show that the conversion efficiency has improved about 6%-9% with the proposed dual-frequency ON-OFF control.