6.78 MHz Multi Amplifier and Transmit Coil eGaN® FET based Class-E Wireless Power System Evaluation

One of the recent developments in 6.78 MHz highly resonant wireless power system architectures for increasing power and area capability [1] makes use of multiple amplifiers driving multiple partially overlapped coils. In such systems the coils will couple [2], and amplifiers with low output impedance will tend to circulate energy between them leading to additional losses, poor system performance, and even frequency splitting [3, 4]. In this paper, high output impedance eGaN FET based class E amplifiers [5, 6, 7, and 8] are investigated for suitability in coupled transmit coil wireless power systems. Experimental results show evidence that high output impedance class E amplifiers can be more easily isolated from each other in this configuration and therefore are more likely to load share. This is more important delivering power to receivers that straddle across two or more coils. Furthermore, only GaN FET based class E amplifiers can simultaneously achieve high efficiency and high output impedance making them ideal for this application.