Robert P. Alley

Fabrication method for a winding assembly with a large number of planar layers

Z-folding of flex circuits is presented as a method of fabricating a transformer winding assembly having a large number of conductive and insulating layers. Flex-circuit patterns. for practical winding configurations are described along with a synthesis procedure. The steps to assemble interleaved planar windings from flex circuits are described. Equations relating winding resistance to geometrical parameters are derived for design purpose. >

Design issues for the transformer in a low-voltage power supply with high efficiency and high power density

Circuit model, design feasibility, and design tradeoffs are investigated for the transformer in 1.5-5 V power supplies with high efficiency and high power density. The transformer is constructed from a single or a matrix of pot cores and from interleaved planar windings. It has been determined theoretically and verified experimentally that such a transformer is realizable as long as the loss constraint is not severe (e.g. less than 0.5 W transformer loss per 100 W output). The primary source of loss is the winding, not the core, in 1.5 V/turn design. Measures to reduce the transformer height tend to increase transformer loss or volume. >

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.<<ETX>>

Megahertz transformers for high density power conversion

Transformer designs that achieve efficiencies greater than 99% operating at 2 MHz at power densities in excess of 400 W/in/sup 3/ for the power range of 50-100 W with output voltages of 1.5 V are discussed. To achieve these results, copper density must be increased beyond what is possible with more conventional Litz wire constructions. Instead, multilayer windings are made of copper foil using flex circuit technology. The elimination of external connections between the winding layers by incorporating the interconnections as an integral part of the winding design is described. This results in Z-folded winding structures that can be ultimately interleaved to achieve high copper density, low copper loss, and very low leakage inductance. >

MHz transformers for high density power conversion

The authors discuss transformer designs that achieve efficiencies greater than 99% operating at 2 MHz at power densities in excess of 400 W/in/sup 3/ for the power range of 50 to 100 W with output voltages of 1.5 V. To achieve these results copper density must be increased beyond that possible with more conventional Litz wire constructions. Instead, multilayer windings are made of copper foil using flex-circuit technology. A particular innovation described is the elimination of external connections between the winding layers by incorporating the interconnections as an integral part of the winding design. This results in Z-folded winding structures that can be intimately interleaved to achieve high copper density, low copper loss, and very low leakage inductance.<<ETX>>