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CIRCUITS FOR POWER FACTOR CORRECTION
WITH REGARDS TO MAINS FILTERING

INTRODUCTION
The new European Norms EN 60555 and the international standard IEC555 will impose a limit on the harmonic content of the input current of mains supplied equipment. In practice this will require the addition of a Power Factor Corrector (PFC) at the input of many types of mains operated electronic equipment, for example electronic lamp ballasts, TV power supplies and motor drives. A correctly designed PFC draws a sinusoidal input current from the mains supply, in phase with the mains voltage, and meets the EN60555 norm. It may also provide additional functions, such as automatic mains voltage selection and a regulation of the voltage supplied to the attached equipment. Size and cost optimization of PFCs must include the RFI filter on the input, which prevents interference being fed back to the mains. The addition of the PFC represents another switching stage in the system, meaning that larger amount of high frequency noise is applied to the mains than with a conventional rectifier/capacitor front end, and so additional RFI filtering is required. The amount of fitering needed can be minimized by choosing suitable modulation techniques and mode of operation of the PFC.