Abstract—Conducted electromagnetic interference (EMI) is a major cause of concern in switch-mode power supplies (SMPSs) which commonly use standard pulsewidth modulation (PWM). In this paper, Sigma–Delta (61) modulation is proposed as an alternative switching technique to reduce conducted EMI from an SMPS. The result of using 61 modulation is a spread in the spectrum of the conducted emissions so that large concentrations of power at discrete frequencies are avoided. Experimental time-domain waveforms and spectra of the switching function of first-order and second-order 61 modulators are presented to prove the viability of the scheme for EMI mitigation. These modulators are then applied to a dc–dc converter in an off-the-shelf computer power supply and experimental results show a reduction of roughly 5–10 dB V in EMI emissions over standard PWM modulators. Index Terms—Electromagnetic compatibility, electomagnetic conducted interference, Sigma–Delta modulation, switch-mod
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