Comparison of audible noise caused by magnetic components in switch-mode power supplies operating in burst mode and frequency-foldback mode

In this paper, it is shown that operation of switch-mode power supplies in burst mode (BM) results in lower audible noise than operation in frequency-foldback mode (FFM). However, the selection of the switching frequency in a burst package can have a significant impact on the audible noise. In both BM and FFM, the audible noise can be reduced by decreasing the peak value of current pulses and proportionally increasing the burst frequency in BM and the switching frequency in FFM. In BM, the audible noise can be further reduced if instead of increasing the burst frequency, the number of burst pulses is increased without changing the burst frequency. The presented BM and FFM audible noise analysis is experimentally verified on a dc-dc boost test circuit.