The Engineer’s Guide To EMI In DC-DC Converters (Part 17): Active And Hybrid Filter Circuits

Focus:

There have been numerous efforts over the past three decades in the application of active EMI filters (AEFs), with results indicating a substantial reduction in filter size relative to a passive-only solution. Combining an AEF with a passive component, which creates a hybrid EMI filter (HEF), helps improve the overall attenuation and bandwidth. This article reviews the operation of the six AEF topologies which are categorized according to control method (feedback or forward), sensed noise parameter (voltage or current) and noise injection method (voltage or current). It then demonstrates performance of a buck regulator with an HEF circuit through simulation and explains key details of its design. Finally, a practical implementation of a sync buck regulator with an integrated AEF, TI’s LM25149-Q1, is presented along with its measured EMI performance with and without AEF enabled (relative to CISPR 25 automotive limits) and an illustration of its size reduction versus a passive EMI solution.

What you’ll learn:

• How to reduce EMI filter size in dc-dc converters through the use of active and hybrid EMI filters
• How to implement a buck regulator with an integrated active EMI filter

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Author & Publication:

Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Apr 15 2021

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