The Engineer’s Guide To EMI In DC-DC Converters (Part 16): Common-Mode Input Filter Design

Focus:

CM noise current flows through the earth or system chassis ground (GND) connection and current magnitudes are dictated by the voltage slew rates at the power semiconductor terminals. The CM noise propagation path of a nonisolated converter comprises mainly stray capacitances to GND from the output bus connections and the parasitic capacitance brought by the switching device(s) and heatsink structure to GND. This article reviews theoretical concepts related to dc-dc converter input filter design to minimize CM noise specifically, including selecting the EMI filter topology, estimating the required filter attenuation, calculating the filter component values, and integrating the CM filter stage to reduce the volume and weight of the EMI filter design. A simulation using a SIMPLIS model estimates the expected CM noise based on an input filter for conducted emissions from an automotive synchronous buck converter design.

What you’ll learn:

• How to design an input EMI filter for suppression of common-mode noise

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Author & Publication:

Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Dec 15 2020

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