On-and off state losses in foil windings

High frequency DC-DC converters require transformers that are designed for optimal efficiency, particularly with respect to the copper losses when gapped cores are used. This paper examines the copper losses that arise in foil windings, particularly under open circuit conditions that approximate the conditions that arise in transformers for flyback converter applications. The study uses 2-D and 3-D finite element models to estimate losses in open circuit spiral windings, both interleaved and not interleaved. The validity of 2-D approximate models is evaluated and the effect of air gap placement is examined