Spectral characteristics of random carrier frequency switching in off-line switched mode power supply

In this paper, a detailed analysis and the spectral characteristics of a random carrier-frequency (RCF) technique for suppressing conducted EMI in an offline switched-mode power supply are presented. The analysis provides a theoretical platform for studying the characteristics of this random switching scheme. The level of randomness is defined for the RCF scheme and varied in the power converter example so that its effects on the power spectra can be demonstrated. Theoretical predictions of the spectral characteristics of this scheme are confirmed with measurements. Comparisons of the spectral performance show that the RCF scheme has better conducted EMI suppression than the FM and standard PWM schemes.