Comparison of EMI generated by fly-back converter with other single switch isolated converters

摘要

Fly-back converters are popular in low power ranges because of their simplicity and low component count, but they generate lot of Intrinsic Differential Mode (IDM) noise. IDM noise generated by most of the other single switch converters is comparatively less than that of fly-back. Particularly, IDM noise in converters such as SEPIC and Cuk are negligibly small. They have a potential to compete with fly-back even with complex circuit and more number of components. However, Non-Intrinsic Differential Mode (NIDM) or Mixed Mode (MM) noise offsets this advantage, making DM noise produced by all single switch converters more or less comparable. That makes fly-back still the right choice in low power ranges. This paper presents a comparative study of various modes of EMI noise generated by simulated single switch converters to verify these facts. The effectiveness of Y-capacitor in reducing noise in a two-wire fly-back SMPS is also verified.