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POWERING SWITCHED MODE POWER SUPPLY (SMPS)
(Used in Computers, Monitors, Printers, TV, CFL’s etc.)
Non- linear nature of current drawn by Switched Mode Power Supplies
Power supplies are used to convert AC voltages like 240 VAC to various DC voltages like 3.3V,
5V, 24V, 48V etc. Majority of modern day electronic devices use embedded general purpose
Switched Mode type of Power Supplies (SMPS) to drive the electronic circuitry.
General purpose Switched Mode Power Supplies (SMPS) have one major disadvantage – the
current drawn by them from the AC power source has a non linear waveform (the waveform is
not sinusoidal as the input voltage waveform but is in the form of short, larger value pulses
around the area of + Vpeak and - Vpeak). This is due to the charging of the input filter
capacitor(s) mostly around the positive and negative peak portions of the sinusoidal input voltage.
The degree of non-linearity is measured by the “Crest Factor”.
Crest Factor = Peak Current / RMS Current
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