Optimizing EMI Input Filters for Switched Mode Power Supplies
Published by Rohde & Schwarz Inc.
Almost every switched-mode power supply (SMPS) needs an EMI (Electro Magnetic Interference) input filter to suppress any disturbances of the SMPS on the power lines. This requirement having an input filter in the design ensures that no negative effect will occur in other parts of the systems connected to the power lines. Therefore, the design and the validation of the input filter is a major task during a typical power supply design.
This document will describe a method to separate common-mode and differential-mode separation using two oscilloscope channels. This separation approach works without any additional hardware component like a noise separator. The designer will be able to distinguish between common-mode (CM) and differential-mode (DM) noise. This additional information about the dominant mode provides the capability to optimize input filters very efficiently.