Deflux Windings Benefit Forward Converters But Not Flybacks

Focus:

A common circuit technique to increase the efficiency of low- to medium-power (<1 kW) converters with transductors (multiple-winding magnetic components) adds a winding that conducts current during the on-time to off-time transition, returning the leakage-inductance energy to either the input or output port. This article demonstrates how this technique for defluxing the primary winding works in the forward converter and also, why it is not feasible for flyback converters. This discussion thereby demonstrates the more detailed magnetics behavior of deflux circuits. The method described here for recovering the transformer’s leakage energy is similar in function to active-clamp “reset” techniques, but is simpler as it only requires the addition of a small winding and a diode.

What you’ll learn:

• How to understand the operation of a simple deflux circuit for forward converters and why it’s impractical for flyback converters
• How to improve the efficiency of forward and boost push-pull converters by adding a deflux winding and diode to recover the transformer’s leakage-inductance energy

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Author & Publication:

Dennis Feucht, Innovatia Laboratories, Cayo, Belize, How2Power Today, Jan 17 2020

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