The size of LLC converters magnetics: Frequency dependence

Focus:

In this 14-min. video, the presenter refutes a claim made on LinkedIn that an increase in frequency does not lead to a reduction in the size of the magnetics component(s) for an LLC resonant converter. After explaining how the input inductors and couple inductors required in this topology may be implemented as integrated magnetics on a single core, he works through the math for core selection for the coupled inductors. He derives expressions for core cross sectional area, total winding area, and the product of these two, area product, which can be used to select the core given a desired core loss density. He explains how inductance and Bmax are the frequency dependent terms in these expressions, which ultimately leads to a figure of merit (area product ratio = area product at high frequency/area product at low frequency), which can be used to gauge the potential size reduction achievable for the coupled inductors when frequency is increased. He applies this area product ratio in a design example using vendor core data, demonstrating a 4X reduction in area product at higher frequencies. He adds that the size reduction will be slightly offset by a reduction in packing factor k due to use of litz wire but that leakage inductance will be absorbed in the resonant element and is therefore not a factor.

What you’ll learn:

• How to evaluate the variation in magnetics size versus frequency in an LLC resionant converter
• How to determine core size for the coupled inductors in an LLC resonant converter

View the Source

Author & Publication:

Sam Ben-Yaakov, YouTube, Mar 29 2018

This article summary appears
in the HOW2POWER Design Guide.

The Design Guide offers
organized access to
hundreds of articles
on dozens of power conversion
and power management topics.

The Design Guide search results
include exclusive summaries
and accurate "how to" analysis
to help you make faster,
more informed decisions.

Search
for more articles