Industry White Paper

Optimizing EMI Input Filters for Switched Mode Power Supplies

November 30, 2020 by Rohde & Schwarz

App Note Overview

Most switched-mode power supplies (SMPS) require an EMI input filter to suppress electrical disturbances on the power lines. Thus, input filter design and validation is a critical part of power supplies. The conducted emissions test is a standard validation method that allows a designer to obtain feedback from the system about EMI susceptibility. However, designers need to obtain details about the noise spectrum to optimize the input filter as effectively as possible.

This application note by Rohde & Schwarz describes a method for separating common-mode and differential-mode noise using two oscilloscope channels without the need for any additional hardware, e.g., a noise separator. A dual LISN and mathematical approach is used to calculate common-mode and differential-mode noise using a high-end Rohde & Schwarz oscilloscope.

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