A single-stage 6.78 MHz transmitter with the improved light load efficiency for wireless power transfer applications

A single-stage transmitter is reviewed, which directly converts a utility ac input to high frequency (6.78 MHz) ac output for wireless power transmission. By integrating two stages (totem-pole PFC rectifier and full bridge inverter) into a single stage, the topology achieves high efficiency and reduced component count. In this paper, a simple auxiliary circuit is added to allow the single-stage transmitter to operate in two modes. At heavy load, the transmitter operates as a totem-pole rectifier with PFC and achieves low distortion of the input current. At light load, the circuit operates as a voltage-doubler rectifier (VDR), extending the ZVS range of the transmitter. As a result, hard switching is avoided and efficiency is improved at light load. This improved single-stage transmitter is verified by a 100 W, GaN-based laboratory prototype.