27.12MHz GaN resonant power converter with PCB embedded resonant air core inductors and capacitors

Abstract

This paper presents the design and implementation of a 27.12 MHz, 320 W, 170 V to 28 V dc-dc resonant power converter with resonant inductors and capacitors embedded into the Printed Circuit Board (PCB). Operating at 27.12 MHz allows for small value and size resonant passive components to be implemented using traces on or within a PCB. Previous work [1]-[14] has demonstrated various ways of using PCBs to make inductors and capacitors. In this work, we evaluate a design with goals of achieving good power density, good EMI shielding, (relatively) low manufacturing cost, and the potential to operate in harsh environments (e.g. strong external magnetic field). Specifically, the proposed prototype converter consists of four vertically stacked PCBs. Two low cost 3.2 mm thick FR4 PCBs are used to make the air core toroidal inductors, and the resonant capacitors are implemented using two low-dielectric-loss thin Rogers PCBs and located in the middle of the stack. To help reduce leakage fields from inducing eddy current within the EMI shield, each resonant inductor is formed by the series/parallel combination of two vertically aligned opposite wound toroids placed in different PCBs. In this arrangement, the circumferential currents of the two inductors flow in opposite directions to cancel the axial “one turn” inductance. Capacitors are formed by two thin layers of high frequency laminates to minimize loss and avoid capacitive heating in the lossy FR4 material. A prototype dc-dc converter was built to verify the concept and it reaches an efficiency of 73.6%. A simulated loss analysis is also presented.