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 (Sigma Delta) modulation is pr
oposed as an alternative switching technique to reduce conducted EMI from a
n SMPS. The result of using Sigma Delta modulation is a spread in the spect
rum of the conducted emissions so that large concentrations of power at dis
crete frequencies are avoided. Experimental time-domain waveforms and spect
ra of the switching function of first-order and second-order Sigma Delta mo
dulators are presented to prove the viability of the scheme for EMI mitigat
ion. These modulators are then applied to a dc-ac converter in an off-the-s
helf computer power supply and experimental results show a reduction of rou
ghly 5-10 dB.muV in EMI emissions over standard PWM modulators.