Reduction of EMI by Frequency Modulation in Switching Mode Power Supply
Date Issued
2005
Date
2005
Author(s)
Shei, Chein-Kuo
DOI
zh-TW
Abstract
Employing frequency modulation techniques for EMI reduction in switching converters was reported some years ago and the techniques have been gaining some momentum in actual product applications. There were different modulating schemes reported, including sine-wave modulation, triangular wave modulation, random modulation and bi-frequency modulation. However, the results reported were mostly focused on the mathematical analysis of the resulting EMI spectrum without much discussion on the side effects of the schemes on converter performances.
In this thesis, these modulating schemes were reevaluated and compared. A hardware circuit to modulate the converter switching frequency was designed and built for the experiments. From the experiments, it’s observed that significant output voltage ripple can be caused by the modulating schemes. The transfer function between the output ripple and the modulating signal seems to follow the input-to-output (audio susceptibility) transfer function of a converter power stage but this has not been theoretically derived. The effects of feedback control loop gain on the output ripple are also discussed in the thesis.
Subjects
頻率調變
EMI
Type
thesis
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