How Active EMI Filter ICs Reduce Common-Mode Emissions in Single- And Three-Phase Applications (Part 2): Modeling Ferrite Chokes

by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Feb 15 2024

Focus:
In designing an active EMI filter (AEF) circuit, accurate characterization and modeling of the choke impedance is essential as it impacts filter attenuation and loop stability. Following a review of the impedance behavior of ferrite-cored magnetic components, this article describes a SPICE-compatible behavioral model for a ferrite choke using an intuitive circuit structure, which facilitates accurate EMI simulations for both passive and active filter designs. Using an extraction procedure of model parameters based on small-signal impedance measurements, the behavioral model for the choke impedance can accommodate single-phase two-winding (1p2w), three-phase three-winding and three-phase four-winding chokes. As an example, the modeling procedure is applied to a 1p2w ferrite CM choke for the filter in a server rack power supply.

What you’ll learn:

• How to generate a SPICE-compatible model for ferrite-core common-mode chokes in EMI filters
• How to design active EMI filter circuits

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