US Patent 7948348 Cross-core transformer

Core structures that may be used in transformers to improve the number of turns-ratios available. The core structures may include at least three outer legs and a center leg. In operation windings of the transformer may be wrapped around the center leg (e.g., using a bobbin) a fractional number of times, such that the turns-ratio of the transformer may be more finely selected without increasing the number of turns required. Additionally, the outer legs may have different cross-sectional areas, such that even more fractional turns-ratios are available.