How Active EMI Filter ICs Reduce Common-Mode Emissions in Single- And Three-Phase Applications (Part 5): Improving Immunity To Low-Frequency Disturbances

by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, May 15 2025

Focus:
A compact design of the EMI filter is vital to meeting packaging specifications in high- density ac-dc power supply applications. By shrinking the size of toroidal-cored common mode (CM) chokes, an active EMI filter (AEF) circuit for CM noise attenuation can considerably reduce the size, weight and cost of the overall power-circuit implementation. This new installment in the AEF series addresses the problem of AEF amplifier saturation, which can result from the presence of low-frequency CM disturbances at the filter’s input port. A multiple feedback technique is described that improves the AEF circuit’s immunity to CM disturbances below 150 kHz while preserving the filter attenuation of emissions above 150 kHz. Simulations and experimental results validate the proposed solution.

What you’ll learn:

• How to prevent low-frequency common-mode disturbances from saturating the amplifier in an active EMI filter

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