What is PFC on a Power Supply?

[leegroves]

I've been looking into buying a 24-pin power supply and I noticed some have PFC. Some have active or passive PFC. What is this and what's the difference between active and passive? DO I need it?

 

[theMan]

http://www.endpcnoise.com/cgi-bin/e/pfc.html

 

[Tostada]

Originally posted by: theman
http://www.endpcnoise.com/cgi-bin/e/pfc.html

Don't listen to that site. They're trying to sell PSUs with PFC. It's not exactly lying, but it's deliberately misleading. They are being extremely deceptive with the term "efficiency." They are actually talking about apparent efficiency, which is irrelevant for most people.

What PFC does is it reduces phase harmonics. Businesses have 3-phase power coming in and they pay for their power differently. PFC puts less stress on the power grid, which reduces power costs for businesses. For residenal use, the only benefit to PFC is that it puts less stress on your UPS if you have one.

If two PSUs were identical except that one had PFC and one didn't, getting the one without PFC would save you a little on your electric bill and really has no down-side unless you're using a cheap UPS that can't handle it. For example, I have a crappy 5-year-old 700AH UPS that used to beep at me about once a week until I got a PSU with PFC.

Here's some legitimate info on PFC:
http://www.silentpcreview.com/article28-page5.html

The bottom line is that PFC usually should not be a deciding factor in buying a PSU. Better PSUs almost always have PFC. With an expensive PSU, you generally don't have the option to get a non-PFC model. Expensive PSUs are usually more efficient, though, to a degree that more than makes up for the inherent ineffeciency of PFC. SeaSonic S12 PSUs all have PFC and have over 80% real efficiency.

 

[Zepper]

In a corporate situation with numerous PCs, they could save some money on their power bill. No PFC will have a PF of around 0.5, passive PFC will get around 0.7 or so under a narrow range of circumstances while aPFC (active PFC) will get 0.9 or better (1.0 is maximum - my Sparkle/Fortron gets 0.97).
. Another thing you usually get with aPFC (not connected but for the fact the circuitry will be on the same additional PCB) is autoranging on the AC side which allows the PSU to run on from ~90 - 240V at 50/60Hz. So your system would be much more tolerant of line conditions. You may also get a few more minutes of backup time out of a given UPS.
. And then there's always the prestige factor.. aPFC is usually only found in the top models in a line. It always gives one a warm and fuzzy feeling to own the high-line product.
. Silverstone sells some good Enhance-made PSUs with aPFC - available at Newegg et al.

.bh.

 

[Auric]

Reduced EMI/RFI for the user too. I don't know about in the EU where it is mandatory but in NA there prolly are not many light-weight el-cheapo PSU's with Active PFC so as said it can be a good indicator of quality.

 

[John]

Originally posted by: leegroves
I've been looking into buying a 24-pin power supply and I noticed some have PFC. Some have active or passive PFC. What is this and what's the difference between active and passive? DO I need it?

1) http://www.seasonicusa.com/support.faq.php

2) No.

 

[Pariah]

All you've ever wanted to know about active and passive PFC and probably even some you didn't want to know:

PFC decoded

 

[Painkiller]

For large business with lot of computers then Yes. For home, not that important.

 

[fstime]

Its not very importent for the average user.

Most top of the line PSU's come with it either way.