In this webinar Robert Schillinger (Würth Elektronik eiSos) and Marcus Sonst (Rohde & Schwarz) explain how to go about debugging conducted EMI issues in a flyback power supply (PSU) design by using an oscilloscope and some additional equipment like a LISN. You will gain a deeper insight into the noise sources of a SMPS, and what kind of filtering you might have to add to pass compliance testing in an EMC laboratory. At the end of the presentation, you should be able to distinguish between differential mode (DM) and common mode (CM) and how to find the dominant mode.

Use a LISN

A LISN or Line Impedance Stabilisation Network is used to measure the conducted interference emissions of a test object. It is used for basic pre-compliance testing in an ordinary lab and will most likely make testing in a full-compliance test laboratory for EMI certification later on less costly because less or no changes have to be made to a design. A full compliance test in a certificated lab is expensive.
 

Resources

Presentation slide deck & LTspice simulations
Detailed LISN project description
Elektor 9-10/2021: EMC Pre-Compliance Test for Your DC-Powered Project (Part 1)
Elektor 11-12/2021: EMC Pre-Compliance Test for Your DC-Powered Project (Part 2)