Oh, the things you can learn trolling the aisles at tradeshows and talking to engineers! There was lots to check out last month at Power Systems World in Detroit.
Tabtronics CTO Victor Quinn presented a seminar about evaluating transformer dissipation and energy storage in switch-mode power supplies to evaluate transformer designs winding-layer by winding-layer. He developed a rigorous comparison of solenoidal and planar transformer performance and looked at several versions of planar conductor configurations, including pc-board, flex-circuit, and annular-wound magnet wire for offline applications. You can request copies of the presentation at www.tabtronics.com.
At International Rectifier's booth, Carl Blake told me about the link in power supplies between upstream heat and downstream performance. He said cutting the heat the ac-dc rectifiers dump into the circuit board improves downstream dc-dc converter rectifier efficiency. You can do that if upstream rectifiers are in IR's DirectFET surface-mount (SMT) package—which has a metal lid bonded to the drain—instead of SO-8s. Of course, you need air flow.
Blake showed me several prototype supplies using the new 40- and 100-V DirectFETs. IR had measured temperatures and efficiencies with 400-LFM flows and found primary-side package temperatures around 40°C cooler than equivalent SO-8s and secondary-side package temperatures around 15°C cooler. Overall, efficiency was up better than a percent in that low-nineties range where further gains in efficiency are so hard to come by.
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