Design and Optimization of a Class-E Amplifier for a Loosely Coupled Planar Wireless Power System

In wireless power systems for charging battery-operated devices, the selection of component values guaranteeing certain desired performance characteristics can be a tedious trial-and-error process, either sweeping component values in circuit simulations or changing components by hand. This difficulty is compounded by the variable nature of the load resistance presented by a device under charge. This brief considers component selection for a specific wireless power system architecture, which is an open-loop class-e inverter using a series-parallel arrangement for load impedance transformation. Formulas for the optimal receiver, transmitter, and class-e components are derived given a set of constraints on the resistance, phase, quality factor, and drain voltage waveform. Using a 16 cm times 18 cm primary and a 4 cm times 5 cm secondary coil, the derived formulas are used to build a wireless power system. We show that the system has desirable performance characteristics, including a power delivery of over 3.7 W, peak efficiency of over 66%, and decreasing power delivery with increasing load resistance.