How Active EMI Filter ICs Reduce Common-Mode Emissions In Single- And Three-Phase Applications (Part 1): An Overview

by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Nov 15 2023

Focus:
In space- and weight-constrained applications such as automotive on-board chargers and aerospace power supplies, a compact EMI input filter is one of the main design challenges. Common-mode (CM) filters for equipment with conductive parts accessible to humans typically have limited Y-capacitance because of touch-current safety requirements, thus requiring large- sized CM chokes. Using active EMI filter (AEF) circuits enables more-compact filter solutions. This article introduces the topic of active EMI filtering and provides practical circuit realizations using a new family of standalone AEF ICs (the TPSF12C1 and TPSF12C3) for CM noise mitigation in single- and three-phase systems. Measured results from a 3.3-kW totem-PFC stage illustrate the benefits of EMI reduction and board-space savings. This article begins with a review of conducted EMI standards across the frequency spectrum, including new requirements at lower frequencies. Popular configurations of passive EMI filters for kilowatt-level, grid- connected applications are also presented with discussion of how safety requirements constrain component selection.

What you’ll learn:

• How to reduce the size of CM chokes using active EMI filter ICs
• How to understand operation and benefits of the CM active filter circuit based on the voltage- sense current-inject method

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