What every designer should know about magnetics in switch-mode power supplies

Focus:

This 5-page introduction to magnetics design defines key concepts underlying the operation of inductors and transformers in switched-mode power supplies. The article defines terms such as Lenz's Law, magnetic-field intensity (H), magnetic-flux density (B), Ampere's Law, Faraday's Law, permeability, saturation, total flux or flux linkage, reluctance, Eddy current (and Eddy-current loss), skin effect, proximity effect, and Faraday shield. Analogies are made between magnetic terms and their electrical counterparts. The BH curve is explained and the effect of an air gap in the magnetic core on the BH curve is discussed. The article also discusses how inductors and transformers operate; what core materials are used for different power applications, the effect of eddy-current loss, high-frequency effects on transformer windings, interwinding capacitance as a source of EMI, and other transformer design considerations. Article ends with a brief summary of steps required to design a flyback transformer.

What you’ll learn:

• How to understand magnetic concepts that underlie the design of transformers and inductors for switched-mode power supplies
• How to design a flyback transformer (summary)

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Author & Publication:

Sameer Kelkar, Power Integrations, EDN, Nov 26 2009

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