Why Couple The Windings In A SEPIC?
by Eleazar Falco, Würth Elektronik, Waldenburg, Germany, How2Power Today, Nov 14 2025
Focus:
The SEPIC topology is built with two inductors, which can either be implemented as
separate, uncoupled inductors or as coupled inductors with two windings sharing the same
magnetic core. It is common to hear that either the required inductance or the ripple
current can be “halved” thanks to the magnetic coupling. This article explains why the
ripple current amplitude is reduced when the windings are magnetically coupled, and
quantifies the reduction as a function of coupling factor or leakage inductance. Then, a
design example demonstrates the ripple current reduction and higher efficiency obtained
with actual coupled versus uncoupled inductors of the same volume. The ripple-current
steering caused by winding asymmetry is observed.
What you’ll learn:
- How to determine the reduction in ripple current in a SEPIC as a function of inductor coupling factor or leakage inductance
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