HIgHly resonant WIreless PoWer transfer system overvIeW

Wireless power applications are gaining popularity in many commodity products such as mobile phones chargers. Most of the wireless power solutions have focused on tight coupling with induction coil solutions at operating frequencies around 200 kHz, and Class E, F and S amplifier converter topologies. Recently, however, there has been a push for operation in the restricted and unlicensed lower ISM band at 6.78 MHz where traditional MOSFET technology is approaching its capability limit. Enhancement mode gallium nitride transistors offer an alternative to MOSFETs as they can switch fast enough to be ideal for wireless power applications. This paper will focus on the experimental evaluation of a highly resonant coil wireless energy system using eGaN® FETs in a half bridge topology operating at 6.78 MHz designed to be suitable for multiple 5 W USB based charging loads. The experimental system will further be compared to a similar unit based on equivalent MOSFETs in the power converter stage.