Use of Sigma-Delta modulation to control EMI from switchmode power supplies

Graduation date: 1999Item restricted to the OSU community.Conducted Electromagnetic Interference (EMI) is a major cause of concern in switchmode power supplies (SMPS) which commonly use standard pulsewidth modulation (PWM). In this thesis, Sigma-Delta (ΣΔ) modulation is proposed as an alternative switching technique to reduce conducted EMI from SMPS. The result of using ΣΔ 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 from first-order and second-order ΣΔ\ud modulators are presented to prove the viability of the scheme in EMI mitigation. These modulators are then applied to an off-the-shelf computer power supply and experimental results using FCC-specified methods show a reduction of roughly 5-10dB in EMI emissions over standard PWM modulators