Optimal Switch Timing Circuits for Soft-Switching Converters (Part 2): Circuits for Different Switch Functions

Focus:

In this final part of the article, the author describes circuits that can be used to accomplish optimal switch timing in soft-switching converters. These include circuits to control switch turn-on of the main switch, a clamp or auxiliary switch, and a synchronous rectifier, each of which has different requirements as explained in this article. The article begins by reviewing how the turn-on transition of the switch changes with the amount of energy available to drive the drain-source voltage of the main switch to 0 V. Then, circuits are presented that detect zero voltage across the main switch or a non-zero minimum voltage across the main switch. A delay block, which is needed to turn on the main switch at start up, is briefly described. Next, a zero-voltage detector for an auxiliary or clamp switch is presented and an adaptive gate driver for an auxiliary switch, which provides near-optimal timing in exchange for other benefits, is described. Finally, an optimal timing circuit for a synchronous rectifier is described.

What you’ll learn:

• How to design gate-drive timing circuits for optimal or near optimal switch timing in turning on the various switches in soft-switching power converters

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Author & Publication:

Ernie Wittenbreder, Technical Witts, Flagstaff, Ariz., How2Power Today, Feb 16 2016

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