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DESIGN TIPS High Frequency Power Inductor Design In this article we continue the theme of custom versus off the shelf magnetics design The relatively simple output inductor of a forward converter is used as an example to show the issues and pitfalls involved in trying to use off the shelf inductor designs for high frequency power supply applications By Dr Ray Ridley Ridley Engineering Power Inductor Design for overcurrent situations When I first started my career in power electronics over 25 years ago all magnetic components were custom designed and manufactured In our current power supply design workshops we dedicate an entire day to the theory and practice of making custom inductors for switching power supplies Attendees at the course design analyze and build their own inductors and transformers in the lab 1 In the last few years numerous companies have developed kits of standard parts aimed at the semiconductor companies to integrate into their designs This proliferation of parts has recently led me to wonder if custom inductor design was becoming a skill belonging more to the past than the future The off the shelf inductor also 47 H had a single number assigned to it on the parts kit a current rating of 5 A Since the parts kit is aimed at the nonexperienced power supply designer it seems reasonable to assume that the inductor is suitable for a 5 A converter application Figure 2 shows two inductor designs one developed in our workshop for a rugged 60 W converter and the smaller low cost off the shelf part You can see a significant size advantage of the standard component The 47 H custom inductor was designed to operate continuously at 5 A with plenty of margin Figure 1 Building custom magnetics in our design workshop 14 The parts are quite different in their design as shown in Fig 3 The custom made inductor has a singlelayer winding on an RM8 core with a gapped center leg The windings are a significant distance away from the center leg gap essential to avoid



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