Development of a DC-to-DC power converter

A 2 in.×1 in.×0.18 in. planar transformer (consisting of two main transformers and four auxiliary transformers made of a low-profile magnetic structure and multilayer PWB windings) was fabricated and used in an interleaved flyback power converter. Power-train efficiencies greater than 80% were obtained at various input voltages, loads and temperatures using a 1 MHz, constant-frequency, pulse-width-modulated, zero-voltage resonant-transition switching technique. The highest efficiency observed was 85%. The results indicate that the planar transformer functions satisfactorily in an interleaved flyback power converter. However, power loss calculations result in 2 W unidentified losses when compared with the actual circuit performance. When discrete capacitors were replaced by a capacitor array substrate and the discrete MOSFET switches were replaced by MOSFET dies mounted on the capacitor substrate, the power conversion efficiency degraded 8%. This was attributed primarily to the extra lead resistance introduced by mounting the dies on the substrate. This loss could be reduced by improving the capacitor substrate metallization design