The Engineer’s Guide To EMI In DC-DC Converters (Part 15): Differential-Mode Input Filter Design
by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Oct 15 2020
Focus:
Modern dc-dc converters generate substantial conducted electromagnetic interference
(EMI), both differential mode (DM) and common mode (CM), as a side effect of high-
frequency and high-edge-rate switching. Here in part 15 of this ongoing series, this
article reviews theoretical concepts related to input filter design to minimize DM
noise specifically, including selecting the filter topology, estimating the required
filter attenuation and calculating the filter component values. Basic expressions are
given for calculating component values for a pi-filter. A simulation provides the
expected attenuation based on an input filter for conducted emissions from an
automotive synchronous buck converter. Article discusses the importance of impedance
mismatching in filter design.
What you’ll learn:
- How to determine the required attenuation of differential-mode EMI required from the input EMI filter in dc-dc converter applications
- How to select an EMI filter topology in dc-dc converter applications
- How to calculate component values for a differential-mode EMI filter
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