Types of electro magnetic interferences in SMPS and using Y-capacitor for mitigation of Mixed Mode noise

The EMI generated by SMPS is an important topic for research because international EMC regulations have become stricter. Many papers have been published in this area. This paper is an effort to briefly review the categorization of various modes of noise generated by SMPS with fly-back converter topology. The effect of Mixed Mode noise is similar to Differential Mode noise but its sources are same as Common Mode noise. Therefore, Y-capacitors can be used to mitigate them. Frequency ranges of different modes are analyzed to show that DM noise is dominant in lower frequency ranges, CM noise is dominant in mid ranges and MM noise in higher ranges. A case study is then presented to investigate the effective use of Y-capacitor for the mitigation of Mixed Mode noise. The discussion is supported by experimental results.