High-Q resonator with integrated capacitance for resonant power conversion

Resonant power conversion at MHz frequencies is useful for miniaturization of power electronics, but requires resonators or inductors with high efficiency. Because litz wire is not effective above several MHz, an alternative winding structure for inductors is required for operation at these frequencies. In this paper, we present resonators with a multi-layer foil winding which can be constructed using industry-standard polyimide laminates. The proximity effect losses are reduced due to current sharing between multiple conductor layers much thinner than a skin depth. The integrated capacitance of the resonator eliminates the need for a physical connection between the inductor and the capacitor required in a typical LC resonant tank. Low-loss NiZn ferrite cores were used to straighten field lines to reduce lateral current crowding. Prototypes of both parallel and series resonators achieved quality factors over 800 in the 7-9 MHz range, confirming the theoretical analysis of multi-layer foil windings.