The Small-Signal Model Of An Active-Clamp Forward Converter (Part 2): Active-Clamp Forward Converter Operation

by Christophe Basso, ON Semiconductor, Toulouse, France, How2Power Today, Mar 14 2014

Focus:
Use of a third winding to reset the transformer core in the classical forward converter has drawbacks in terms of stress on the power switch and the reliance on hard switching. The active-clamp reset technique not only limits the voltage excursion on the power transistor drain at turn-off, it also helps achieve near-zero voltage switching operation under certain conditions. When switching losses are minimized, it becomes easier to increase switching frequency and shrink magnetics. Here in part 2 of this article series, the structure of the active-clamp forward converter is introduced, its operation is explained, and a large-signal model is derived, enabling SPICE simulation of the converter and generation of its Bode plot. These steps set the stage for derivation of a small-signal model and a complete control-to-output transfer function for the active-clamp converter in part 3. At the end of this part 2, a nice list of references provides further reading for those seeking more-indepth analysis of the active-clamp forward converter and its history.

What you’ll learn:

• How to understand the operation of the active-clamp forward converter
• How to derive a large-signal model of the active-clamp forward converter

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