A study of power factor and harmonics in switched-mode power supplies

Power factor and harmonic characteristics of high frequency switched-mode power supply systems operating in discontinuous inductor current mode are studied in this paper. The study is based on the fact that virtually all power factor correction (PFC) converters use a few basic converter topologies as their input stages. It is found that these converters present distinctive harmonic behaviors. Harmonic current contents and the resulting power factors that are associated with these converters under different conversion ratios are obtained analytically. The results can facilitate PFC power supply designers in choosing appropriate circuit topologies and estimating the input characteristics of their design.