6.78 MHz self-oscillating parallel resonant converter based on GaN technology

This paper describes the design of a 6.78 MHz self-oscillating parallel resonant power converter for wireless power transfer applications. By sensing just the polarity of the tank inductor current to generate the switch control signals, the system is able to auto-start and self-oscillate at the desired frequency only by applying power to the input port. Different current sensing techniques, including a current sensing transformer and a series resistor followed by a high-speed differential amplifier, are compared based on bandwidth limitations and noise rejection considerations. Furthermore, delay-compensation networks are included in order to mitigate effects of the propagation delays added by signal processing components in the feedback path. It is shown that the circuit is capable of meeting the A4WP/AirFuel standard specifications for wireless power charging. Both inverter and inverter+rectifier configurations are tested and their performances are verified by simulations and experiments on a 16 W prototype using GaN power devices, showing an efficiency of 98 % and 83 %, respectively.