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Information for Magnetics Designers

Most of the information on this site assumes you are already fairly proficient with magnetics design. If not, see below for suggested beginners' references.

High-Frequency Winding Loss

It is well known that the resistance of wire goes up with frequency because of skin effect. Less well-known is that in windings, the high-frequency loss effects are much worse than would be predicted just based on skin effect. Generally, this effect of bunching conductors together is termed proximity effect. If this concept is new to you, see the references references below, particularly the notes by Lloyd Dixon. If it is not new to you, you may be familiar with the common 1-D approximation often called the Dowell method. However, Dowell's analysis can have errors as large as 60% for simple layer-wound windings, and much higher error when air gaps or 2-D winding arrangements change the field configuration. So better methods are often needed to design or optimize high-frequency windings. Here are some of the tools and information available here on that topic. See the publications page for a full list of papers, and the software page for more information on the software tools we have available.

Core Loss

Manufacturers' core loss data is based on sinusoidal waveforms.  But actual power electronics waveforms are rarely sinusoidal. The "Generalized Steinmetz Equation," explained in the paper "Accurate Prediction of Ferrite Core Loss with Nonsinusoidal Waveforms Using Only Steinmetz Parameters" and implemented in software available on the software page. The new method overcomes problems with the "Modified Steinmetz Equation" and requires no data other than that provided by the manufacturer.


High-performance components can be difficult to measure. See "Impedance-Analyzer Measurements of High-Frequency Power Passives: Techniques for High Power and Low Impedance" for evaluation of performance of some instruments and some special techniques.

Suggested references for beginners:

These two textbooks have good introductions to magnetics design in the context of power electronics:
  • Erickson, R.W. and Maksimovic, D., 2001, Fundamentals of Power Electronics 2nd Edition, Kluwer Academic Publishers, ISBN: 0792372700.
  • Krein, P.T., 1998, Elements of Power Electronics, Oxford University Press, ISBN 0195117018.
Some of the best explanations of high-frequency winding effects, as well as magnetics design in general, are in notes written by Lloyd Dixon for seminars held by Unitrode, now part of Texas Instruments. TI has made these notes available online (see the "archived unitrode design seminars"), and even has a  five-module tutorial available for streaming on-line, presented by Lloyd Dixon himself. The notes are also collected as part of the materials you can download when you enter the tutorial.

The Power Source Manufacturers Association (PSMA) offers a number of interesting titles on their current publications page, including:

  • J. K. Watson, c.1980, Applications of Magnetism (reprinted 2008). A classic text that explains the physics of magnetics from an electrical engineering approach and discusses applications extensively.
  • Rueben Lee, Leo Wilson, and Charles E. Carter, 1988, Electronic Transformers and Circuits, 3d ed. (reprinted 2007). A practical treatment of transformer and inductor design.
  • Eric Snelling, 1988, Soft Ferrites: Properties and Applications, 2d ed. (reprinted 2006). Another classic, which, in addition to discussing ferrite materials, contains excellent discussions of power transformer and inductor design and winding design considering high-frequency losses.

For comments or questions e-mail: Charles.R.Sullivan@dartmouth.edu.
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