Evaluation of trade-offs in transformer design for very-low-voltage power supply with very high efficiency and power density

Design methodology and trade-offs have been presented for a transformer in low-voltage (1.5-5 V) power supplies intended to meet 95% efficiency and 100 W/in/sup 3/ power density. The design is based on the pot core geometry, which has low core loss, and the planar toroidal winding geometry, whose mechanical and electrical parameters are highly controllable and reproducible by modern fabrication processes. To achieve high power density in the presence of skin and proximity effects, the primary and secondary winding layers are interleaved to increase the effective thickness. Leakage inductance is reduced, and winding capacitance is increased as a result. The design equations have been coded into a computer program that selects the transformer with the lowest volume over specified ranges of optimizing parameters, such as power loss and flux density.<>