Coupled Inductors Improve Multiphase Buck Efficiency

Focus:

Multiphase buck converters use ripple cancellation to achieve lower output ripple than comparable single-phase buck converters. Ths standard approach to building multiphase buck converters is to use magnetically independent (i.e. uncoupled) inductors in each phase of the output stage. However, there are performance advantages to using coupled inductors (multiple inductors built on a single core) in these converters. Even though the switch from uncoupled inductors to coupled inductors does not lower the output ripple further, it can reduce the amount of ripple per phase and that leads to lower losses per phase and better converter efficiency. Alternatively, use of coupled inductors allows for the same values of phase ripple to be achieved with lower values of inductance, which results in faster transient response. Other possible benefits of coupled inductors include a reduction in output capacitance or a reduction in switching frequency. To explain why these benefits are possible, the article presents an analysis of a two-phase buck converter with uncoupled inductors and a similar analysis with coupled inductors. the same analysis can be extended to multiphase converters with higher numbers of phases.

What you’ll learn:

• How to understand the performance advantages of using coupled inductors in multiphase buck converters
• How to increase transient response without increasing the ripple per phase in multiphase buck converters
• How to calculate ripple currents in each phase of a multiphase buck converter

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Author & Publication:

John Gallagher, Field Applications Engineer, Power Division, Pulse, San Diego, Power Electronics Technology, Jan 01 2006

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