Conducted emi mitigation in switched mode dc-dc converters by spread spectrum techniques

In this paper effectiveness of spread spectrum modulation techniques to the electromagnetic interference (EMI) suppression is investigated. Comparative evaluation of spread spectrum methods is reviewed and demonstrated with the aid of function generator and EMI receiver. Obtained results indicate advantageous features of random carrier fre- quency modulation (CFM), which results in more steady spectral distribution. For a switch mode dc-dc converter, random CFM is systematically tested. This study has indicated the adequacy of quasi-peak detector of EMI receiver to char- acterize the spread spectrum techniques. Based on input con- verter current measurements using EMI receiver, conducted emission spectra are evaluated in function of the defined randomness index R and frequency range. For the acceptable range of R variations up the 20dB EMI suppression level was reached.