Q: What does PFC do?
A: PFC stands for Power Factor Correction. It is now a required feature for all power supplies sold in Europe. Basically it allows power to be distributed more efficiently from the electrical company to your PC system. The following is for the readers who are curious and patient about learning what PFC does.
One of the leading topics in line-operated power-converter design is to take power from the grid but not give any back. In other words, wall plugs should present to the AC source a resistive (and not a reactive) load. A power-factor corrector is the interface between the AC line and power converter that achieves this. So what is power-factor correction and why does it matter?
A Power Factor Corrector is a resistive load to the AC source. It provides a regulated DC output as input to an ordinary converter. Typical power supplies have as input a full-wave bridge rectifier followed by a storage capacitor. While the bridge diodes conduct, the line is driving an electrolytic capacitor – a nearly reactive load for the line. A reactive load causes line voltage and current to be out of phase, which is sub-optimal for power distribution. Maximum power is delivered when they are in phase.
The Power Factor is the cosine of the phase angle. A resistive load has a phase angle of zero and a PF of one.
Furthermore, instead of dissipating (that is, keeping) power, reactive loads store it and give some back later. This causes waveform distortion and harmonics on the AC line, defiling its purity. Line noise, surges, and dips reduce power quality. The developed world is now at the stage where "Electrical Environmentalism" is requiring clean treatment of the line from its users.
A PFC appears resistive to its source. This implies that the input current must differ from the sinusoidal source voltage by only a scaling factor. Their waveforms must be identical, though scaled by the effective input resistance of the PFC, by Ohm's Law.
It should be noted that PFC is usually not needed in US because of the stability of the power stations and their matured design in supplying the power to every home in US. A UPS back up power unit, on the other hand, is a much needed device in some areas where power surges seem more common.
Q: Why should I buy a good quality power supply? Don't they all work the same?
A: A common wisdom that always holds true is, "You get what you pay for", and power supply is no exception. Generally speaking, a better power supply yields greater and more stable performance in areas you may not notice right away, like less crashes or "Blue Screen of Death" with older Microsoft operating systems. This will be more obviously when you open multiple windows or applications and the computer suddenly seems to go much slower. While the amount of RAM plays into this issue, a lot of people don't realize so does the power supply. Furthermore, with the advent of ever faster graphic cards, it will really test a power supply and seperate the lower quality from the true performer. A better quality power supply can actually save you time and troubles by doing it right the very first time.
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