By
Henry W. Ott
Henry Ott Consultants
48 Baker Road, Livingston, NJ 07039
Phone: 973 992-1793 e-mail: h.ott@att.net Fax: 973 533-1442
Abstract: Most people try to fix their common-mode emission problem without first understanding the basic cause of the problem. This at best leads to a trial and error approach to the solution. Therefore, this seminar starts out with a discussion of what causes common-mode emission problems and how common-mode currents are generated. This requires an understanding of what I like to call "the invisible schematic," as well as some basic principles of EMC. Once the source of the problem is understood, the control techniques become fairly straightforward and obvious. They are not "black magic."
A discussion of the applicable FCC and European Union EMC regulations, and the difference between them, is also included. Knowledge of these regulations is important, since they determine the allowable magnitude of the common-mode emission -- and hence the degree of mitigation required.
This seminar then goes on to describe basic control techniques, which include filtering, grounding, and shielding. This is followed by examples of these techniques applied to a switching power supply, and a high power IGBT motor drive circuit. The presentation concludes with a discussion of some simple techniques for measuring the common-mode emission -- since only by measuring the emissions, can you determine the effectiveness of your solution.
This is an in-depth presentation on the subject of common-mode emissions and is intended for an intermediate level audience.
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