Operating Cycle Performance, Lost Periodicity, and Waveform Distortion of Switch-Mode Power Supplies

This paper investigates the performance of switch-mode power supplies used in desktop PCs (PC-SMPS') across the entire range of operating powers. Experimental results show that at low to medium operating powers, the input ac current might lose its periodicity with supply voltage frequency, when PCS-MPS' can be an unexpected source of interharmonics and dc component. In such cases, there is a significant increase of PC-SMPS' current waveform distortion and a substantial decrease of efficiency and operational power factors, which requires application of appropriate measurement and calculation procedures during the analysis. To correctly assess these power-dependent changes in performance and power quality indicators, this paper introduces a novel testing and evaluation methodology, based on the known or assumed PC-SMPS operating cycle.