Showing papers by "Khai D. T. Ngo published in 1991"

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

Abstract: Z-folding of flex circuits is presented as a method to fabricate a winding assembly having a large number of conductive and insulating layers. The process starts with a flexible sheet which contains a copper laminate bonded to an insulating laminate. Conductor patterns are then etched on the laminates and are interleaved and folded to realize the winding assembly. A large number of thin, wide turns can be connected in series or in parallel automatically during the patterning and etching processes, thus eliminating external soldering or conductive vias. Equations relating winding resistance to geometrical parameters are derived for design purposes. A product of the z-folding technique is shown, which is a transformer with a primary winding and one-turn center-tapped secondary windings. >

Method of making conductive film magnetic components

Abstract: A conductive film magnetic component such as an inductor or transformer includes a conductive film winding having a generally serpentine configuration when disposed in a plane. This film is folded to form a stack of layers with each "layer" comprising part of a winding turn and with successive "layers" connected at the folds via the continuous conductive film. The conductive film may be self-supporting and coated with a dielectric layer or may be disposed on a dielectric membrane. The film and membrane are preferably patterned photolithographically.

Effect of height on power density in high-frequency transformers

Abstract: The effect of height on power density is examined for the practical ranges of power, frequency, loss, and volt-per-turn. Relevant mechanical and electrical equations are derived and applied to an optimization algorithm which searches for the design which maximizes the power density at a given height. It has been found that the curves of power density versus height exhibit a peak, on the order of 1000 W/in/sup 3/ in several cases, at a critical height between .25 to .3 in. Below this critical height, the power density decreases drastically. >

Megahertz transformers for high density power conversion

Abstract: 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

Abstract: 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. >