Analyzing voltage ripple in variable-frequency DC/DC boost converter

Numerous variable-frequency (VF) EMI-reduction schemes have been proposed over the last decades. The aim of these VF or spread-spectrum techniques is to reduce both the measurable and effective undesirable electromagnetic noise of a switch mode power supply. Conducted RF-interference measurements have been reported in literature. However, low frequency output voltage ripple has been considered as a major problem in VF DC/DC converters and the majority of these papers do not consider this aspect of VF operation. Analysis of the output voltage ripple with four different VF techniques in six different configurations is made in this paper, and prototype measurements with a boost converter are presented.