Inductor design for VHF tapped-inductor dc-dc power converters

The design and fabrication of coupled inductors with low profile, low cost, and high power density for tapped-inductor high-step-down dc-dc power converters in the very high frequency (30-300 MHz) range are presented. The inductor consists of a multi-layer thin-polyimide printed circuit board (PCB) and nano-granular thin-film magnetic material deposited on both sides and on beveled cuts to form a fully linked closed core. The magnetic material Co-Zr-O has good soft magnetic properties, high resistivity and high flux density capability. Multi-layer Co-Zr-O/ZrO₂ thin films are used to improve the performance of the magnetic core. A winding loss model of this coupled inductor is presented. Coupled inductors with turns ratios 2 and 10 for several different converter applications have been fabricated.