The Effect of Duty Cycle on Suppressing EMI Level in Random Carrier Frequence Modulation of PWM

Random carrier-frequency (RCF) modulation has been applied to DC/DC converters, reducing conducted EMI significantly. The selection of the duty cycle is critical in terms of suppressing EMI level in RCF modulation. But limited related literature is available. In this paper, we analysis the effect of duty cycle on suppressing EMI level by deduced the expression of the amplitude of switching voltage power spectra under the RCF mode and describe the change trend of PSD versus f in the case of different duty cycle, providing the theoretical basis of selection of duty cycle for low EMI level.