Examination of Different Spread Spectrum Techniques for EMI Suppression in dc/dc Converters

Abstract

Examination of different switching frequency modulation techniques (SFMT) for electromagnetic interference (EMI) suppression in dc/dc power converters is presented. The techniques under investigation are sinusoidal (with modulating frequencies 2 kHz and 5 kHz), pseudo-random (with uniform and normal probability distributions of modulating signal) and pseudo-chaotic SFMT. All the techniques are applied to digitally-controlled buck converter of Microchip dsPICDEM SMPS Buck Development Board. Free-wheeling diode voltage of the buck converter operating at switching frequency of 300 kHz and exposed to switching frequency deviation ranging from 0 to 60 kHz is analyzed in order to show effectiveness of such techniques in terms of EMI attenuation. Concerning with possible undesirable side effects in the form of excessive output voltage ripples, the experiments are accompanied by output voltage control of the converter. Analysis of the results obtained reveals that there is need for trade-off between EMI attenuation and output voltage ripples. The pseudo-chaotic SFMT shows the best results from the standpoint of this trade-off. Pseudo-random SFMT with uniform probability distribution of modulating signal gives better EMI attenuation than the other techniques, but output voltage ripples are also larger. That is why this technique can be used for applications, where high EMI attenuation by use of small switching frequency deviations is of primary importance. Ill. 6, bibl.12 (In English; summaries in English, Russian and Lithuanian).