Frequency modulation techniques for EMI reduction in SMPS

Frequency modulation (FM) techniques have been used to reduce EMI of synchronous digital systems working in the range of hundreds of MHz. The working principle consists of modulating the clock frequency in order to spread the energy of each single harmonic into a certain frequency band, thus reducing the peak amplitude of EMI at the harmonics frequencies. Nowadays the switching frequency of power converters has increased up to values which allow the application of frequency modulation to reduce EMI. The paper summarizes some theoretical principles of FM techniques applied to the switching frequency and shows the effectiveness, in terms of EMI reduction. Experimental tests are presented for validation, evaluating also the possible side effects on the converter efficiency and supply harmonics