6.78 MHz Wireless Power Transmitter Based on a Reconfigurable Class–E Power Amplifier for Multiple Device Charging

This article presents a 6.78 MHz wireless power transmitter based on a reconfigurable Class-E power amplifier for various and multiple device charging. To maintain high-efficiency for various power receiving devices, an optimized offset transmission line based on lumped components and a susceptance switching circuit are proposed at the load network of the differential Class-E power amplifier. The offset transmission line changes the load impedances of the Class-E power amplifier for the various receivers to the high-power and high-efficiency region. In addition, the susceptance switching circuit further shifts the load impedances of the Class-E power amplifier for some receivers to the high-power and high-efficiency region. To verify the proposed offset line and susceptance switching circuit, a 6.78 MHz wireless power transmitter was implemented and verified for various receivers. For three different receivers, the transmitter maintains optimal transmission efficiencies for received power levels of 39.7, 16.3, and 8.5 W. A peak system efficiency of 81.4% was achieved when the received power is 31.9 W. The system efficiency maintained well around 74.2 and 70.6% for the received power of 16.3 and 8.5 W, respectively.