EMI suppression with switching frequency modulated DC-DC converters

High frequency power semiconductor switches in power converters generate common-mode and differential-mode conduction noise in addition to radiated noise and cross-talk. Compliance with existing EMI standards is expected of switch mode power converters after fabrication. This article discusses a methodology to mitigate conducted noise effectively at the point of its origin using switching frequency modulation. The switching frequency modulation of DC-DC converters results in redistribution of harmonic energy and consequent suppression of peaks in the switching frequency harmonic components. This phenomenon is clearly visible in the experimental results. Therefore it is evident that the size of the EMI filter can be reduced significantly with the suppression of peaks of switching frequency harmonic components by spreading the spectrum appropriately as described in this article. Moreover, the switching frequency modulation can reduce radiated interference as it lowers the peaks of the harmonic components in current carrying conductors