This paper presents the design optimization of a capacitively isolated coupled-inductor (CI2) resonant DC-DC converter suitable for consumer electronics applications. The converter achieves a low profile using PCB-embedded isolation, a high power density by operating at multi-MHz frequency, and a high efficiency using a coupled inductor based design which reduces the inductance requirement itself. The coupled magnetic structure is realized using an air-core toroid optimally designed to fit within a given total area while achieving the minimum loss. A design methodology for the proposed isolated converter is outlined and a significant loss improvement is shown to be achievable using the coupled design. Two capacitively isolated DC-DC converter prototypes are designed and built using the proposed method - one with separate inductors on primary and secondary sides and one with them coupled. The prototype with the coupled inductor is experimentally shown to achieve 26% reduction in losses.
