Jennifer D. Pollock

Gapped-inductor foil windings with low AC and DC resistance

A new configuration for foil windings in gapped inductors reduces AC resistance while maintaining very low DC resistance. Thus, it is particularly valuable for current waveforms composed of a large DC component with high-frequency ripple. The new technique is applied to an example 50 /spl mu/H inductor in which several different winding cross sections are compared. Finite-element simulations confirm that losses can be reduced by a factor of five relative to standard foil windings.

Predicting inductance roll-off with dc excitations

Predicting variations in inductance of an inductor under different dc bias current conditions is investigated for several different magnetic core materials. A method is presented that allows this constraint to be incorporated into the optimization of an inductor for power conversion applications. Theoretical predictions of an inductors saturation characteristics are compared to the measured performance. The method can be based on characteristics from a magnetic material datasheet or on characteristics extracted from measurements.

Easy-to-use CAD tools for litz-wire winding optimization

Existing advanced and powerful techniques for optimizing litz-wire winding designs are complex and usually require using multiple expensive software packages. A new CAD tool has been created to make advanced litz-wire design methods available to any designer through an easy-to-use web interface. The software performs two-dimensional field simulations and returns designs optimized considering cost and loss. It is shown that simple full-bobbin designs, compared to optimized choices, can result in much higher loss with almost no cost advantage or much higher cost with almost no loss advantage, whereas the optimization results provide a full range of choices providing the lowest loss at any given cost or the lowest cost at any given loss.

The design of barrel-wound foil windings with multiple layers interchanged to balance layer currents

This work investigates the performance of multilayer foil windings in which the layers are interchanged to balance the flux linked by each layer and thus the current is shared equally between layers. Prototype transformers were built to confirm how much of the theoretical loss reduction is achievable in practice. The accuracy of the method to determine the location of the interchange is improved by considering individual turn lengths. In addition, the method is extended to any number of layers and several winding configurations. A discussion of the construction and termination of these windings is included as they greatly affect a components performance.

Modelling Foil Winding Configurations with Low AC and DC Resistance

Significant reductions in winding losses can be achieved by modifying the shape of the cross section of a foil winding. A new method provides improved accuracy for loss calculation in windings with semi-circular cut-outs on gapped cores, as verified by experimental measurements. Optimization using this loss calculation produces designs with up to a factor of two lower losses than either full-width foil windings or litz-wire windings. Foil winding shapes for distributed-gap cores are also introduced and shown to provide reduction in power loss

Loss models for shaped foil windings on low-permeability cores

The cross section of foil windings used in ungapped, low-permeability cores can be modified to reduce total winding loss. The optimal cross-section shape is determined to have a linear cut out and a loss model is developed to calculate the winding loss in foil windings with this cross-section. The loss model shows excellent accuracy when compared to the loss determined by finite-element analysis. The loss model has been used to implement an optimization that determines the lowest loss cross-section for a particular application.

Design considerations for high-efficiency leakage transformers

This paper addresses the design of isolation transformers that integrate all required inductances into one magnetic structure for resonant converters. A design method is presented for components using a power ferrite core, litz-wire windings and an air leakage path. The design method is developed by considering the Q of the leakage inductance to develop a simple and efficient design.

Optimized Magnetic Components Improve Efficiency of Compact Fluorescent Lamps

Further improvements in the efficiency of compact fluorescent lamps can be achieved by optimizing the magnetic components in the electronic ballast. Resonant inductors were evaluated in several commercial integrally ballasted lamps. Winding optimization programs were used to redesign the windings of an example inductor. Two of the proposed winding designs were built and confirmed to provide reductions in winding loss of over 40%