Title page for ETD etd-022199-114952

Type of Document Master's Thesis
Author Qu, Song
Author's Email Address soqu@vt.edu
URN etd-022199-114952
Title Non-Intrinsic Differential-Mode Noise in Switching Power Supplies and Its Implications to EMI Filter Design
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Chen, Dan Y. Committee Chair
Borojevich, Dushan Committee Member
Huang, Alex Q. Committee Member
  • NIDM
  • EMI
  • Filter
  • Switching Power Supply
Date of Defense 1999-02-12
Availability unrestricted

Electromagnetic Interference (EMI) problems in switching power supplies

have been traditionally treated with cut-and-try approaches. In recent years,

advancement has been made to better understand the problems and minimize the

cut-and-try portion of the design process. However, there are still phenomena

difficult to explain in many practical design situations. Often, the problems

may be solved by luck but many puzzles remain unsolved. If not fully understood,

these puzzles are very likely to come back to haunt the designers.

According to the conventional theory, there are two modes of noise: the

Differential-Mode (DM) noise and the Common-Mode (CM) noise. Recently, a new

noise-coupling mode called Non-Intrinsic Differential-Mode (NIDM) noise was

uncovered accidentally in the process of explaining certain EMI filter action [1].

This phenomenon has never been thoroughly studied. The focus of the present

thesis is to investigate the NIDM phenomenon and its implications to practical

EMI filter design issues.

The generation mechanism and basic characteristics of this phenomenon will

be briefly reviewed, which is crucial to the understanding of the remaining parts

of the research. Two essential diagnostic tools are introduced. One is the DM/CM

noise separator and the other is the zero-span mode operation of a spectrum


The results of the investigation will be presented. The results will be

presented using practical examples, which tie the phenomenon to filter design

issues. In some examples, explanations are given to dispel the puzzles commonly

encountered in the practice.

A filter design procedure is suggested for off-line power supplies. This procedure

incorporates the NIDM phenomenon into an existing design procedure. Only first-order

and second-order filter topologies are included in the discussion.

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