Minimize Winding Losses in High-Frequency Inductors

Focus:

Reducing an inductor's losses at high frequencies enables a lower value of inductance and therefore a smaller inductor to be used in power supply applications. For applications with high dc currents, inductors are sometimes wound with foil windings. These foil inductors make efficient use of the winding window and have low dc winding losses, but suffer from high ac winding losses even with low levels of ac current. A new foil winding technique presented in this article overcomes the latter drawback, reducing a foil inductor's losses when operating with high ripple current and high power. The technology, which is offered by West Coast Magnetics, provides the low dc resistance of a foil winding together with the low ac resistance of a Litz-wire winding. Experimental results compare the foil technology with conventional solid-wire, Litz-wire, and full unmodified foil windings. The article also discusses a free magnetic simulation tool called ShapeOpt that enables the designer to optimize the stranding and positioning of Litz wire inside the winding window of gapped power inductors. This winding optimization, which minimizes winding losses, is demonstrated using a sample inductor design. The use of this tool to determine the optimal ratio of winding width to winding height is also discussed.

What you’ll learn:

• How to reduce winding losses of power inductors at high frequencies
• How to reduce the ac winding losses of a foil-wound inductor
• How to minimize winding losses of Litz-wire wound gapped-power inductors by optimizing the winding technique

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Author & Publication:

Weyman Lundquist, President and Engineering Manager, West Coast Magnetics, Stockton, Calif. , Power Electronics Technology, Jul 01 2008

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