what exactly is Active PFC?

nicklaz · Post by **nicklaz** » Thu Jan 09, 2003 6:22 am

what is APFC and how does it affect the noise level of a power supply?

i'm asking because i want to buy a Seasonic SS-300FS but i am confused on which one to get as there is a $30 difference between the one with Active and Passive PFC.

Thanks

BillyBuerger · Post by **BillyBuerger** » Thu Jan 09, 2003 10:19 am

Here is an excerpt. You'll find the full article here:

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

Active PFC

The preferable type of PFC is Active Power Factor Correction (Active PFC) since it provides more efficient power frequency. Because Active PFC uses a circuit to correct power factor, Active PFC is able to generate a theoretical power factor of over 95%. Active Power Factor Correction also markedly diminishes total harmonics, automatically corrects for AC input voltage, and is capable of a full range of input voltage. Since Active PFC is the more complex method of Power Factor Correction, it is more expensive to produce an Active PFC power supply.

Post by **MikeC** » Thu Jan 09, 2003 10:50 am

from my Zalman PSU review:

here's the short and simple on PFC: The basic concept behind PFC is to make the input look as much like a resistor as possible. (A resistor is the simplest electrical load.)

By input, I mean the input as seen by the AC voltage going into the PC. PFC most benefits the electric utility company as less power is wasted at the final delivery stage. PFC is mandated in the EC but not in the US or Canada, as far as I know; we here in North Am benefit from Europe's more enviro-conscious govts as manufacturers usually find it cheaper to make one model than two.

nicklaz · Post by **nicklaz** » Thu Jan 09, 2003 12:02 pm

so, if i understand this correctly, it should affect the noise level of the power supply. correct?

thanks

Post by **MikeC** » Thu Jan 09, 2003 12:33 pm

nicklaz wrote:so, if i understand this correctly, it should affect the noise level of the power supply. correct?

No, not at all. Well very maybe if a non-PFC is so hard to drive that its coils act up & buzz/whine. Think of the AC as the output from the electric company's huge power supply and the PSU in your computer as the device that needs the electricity to run. What PFC does is to make it easier for the electric company's power supply to deliver the electricity to the PSU in your PC. PFC makes the PC PSU look like a pure simple resistance rather than one with inductance and capacitance that are much harder to drive.

In short, PFC has little to do with better/worse, quieter/louder running of the PSU. It has to do with higher electric utility efficiency, which is good from the point of view of energy conservation , enviromentalism and the electric company's profitability.

sgtpokey · Post by **sgtpokey** » Thu Jan 09, 2003 7:47 pm

nicklaz wrote:
so, if i understand this correctly, it should affect the noise level of the power supply. correct?

No, not at all. Well very maybe if a non-PFC is so hard to drive that its coils act up & buzz/whine

But it can make an indirect difference in the form of heat output. I mean, the less efficient a power supply is, the more heat it produces per watt of usable energy, right? Or in other words, when we say a power supply is 70% efficient we're really saying that if the PSU draws 100 watts of power in, it will produce 70 of usable watts of electricity, with the the remainder 30watts being wasted in the form of heat.

At least that's my layman's understanding of Power Factor Correction. If that's the case, the more efficient power supplies would be producing less heat per watt, which could effect a PSU's thermally controlled fans or overall case temps if you don't have a well ventilated system.

Post by **MikeC** » Thu Jan 09, 2003 8:19 pm

sgtpokey,

The efficiency referred to in my last post does not refer to the efficiency of the PC PSU. At least, not in the way we normally think of as PSU efficiency.

To use your example, the PSU draws 100W AC, converts 70W into DC and 30W into heat. You can have an active, passive or no PFC PSU that does this. But what the electric utility has to pump into your home to deliver 100W AC to each of these PSU IS affected by PFC.

PFC does not lower the heat in the PSU or increase its AC/DC conversion efficiency. It is about AC/AC delivery efficiency. If you need to know more, try doing a search on some PS or EE sites.

sgtpokey · Post by **sgtpokey** » Fri Jan 10, 2003 8:10 am

To use your example, the PSU draws 100W AC, converts 70W into DC and 30W into heat. You can have an active, passive or no PFC PSU that does this. But what the electric utility has to pump into your home to deliver 100W AC to each of these PSU IS affected by PFC.

Sorry, I understood what you were saying, but what I was trying to get at was the efficiency rating of the PSU, which according to manufacturer literature, may be a higher % rating in Active PFC PSU's then passive PSU's.

I thought the number that mattered when a PSU generated DC power was it's efficiency rating, and the higher percentage efficiency rating produced more power per watt <- the byproduct of that understanding was in general a manufacturer would claim a higher efficiency rating for it's Active PFC then PAssive PFC units . Is this what the efficiency rating means or does the efficiency rating mean something else?

sgtpokey · Post by **sgtpokey** » Fri Jan 10, 2003 8:26 am

Or maybe I should've just said, a PSU's 2 main environmental attributes are:

1. noise output, which directly affects noise
2. Efficiency rating, which effects the amount of AC power converted into useful DC power (regardless of which form of PFC used). Higher efficiency rating should imply a lower electric bill (probaby only noticeable if you have multiple systems running 24/7) and less heat generated by the PSU (which again may only be noticeable if you have a non ventilated computer room with multiple computers or a severely non-ventilated case).

For a standard quiet psu, the main factor is noise ouput. If you care about heat buildup in extreme cases then efficiency rating may be important.

Post by **MikeC** » Fri Jan 10, 2003 9:23 am

I would generally prefer a PSU with higher efficiency (if the noise is the same). Although the typical efficiency difference like 68% compared to 73% doesn't seem like much, in terms of the heat produced, it is 32% vs 27%. The difference in generated heat is over 15%.

With a mid-line PC that typically does not pull over 150W AC, assuming those numbers above, you're looking at 40.5W vs 37W of heat. Not much. If you have a loaded power machine or dualie that pulls 250W (like Powergyoza's here: http://forums.silentpcreview.com//viewt ... ight=#4974 ) the difference is 70W vs 80W. That's getting bigger.

PSU makers who are tailoring the cooling circuit/fan for minimal noise have to pay close attention to heat (more so than the guys who slap in a 40 cfm at full speed). Higher efficiency will allow them to keep noise lower while still maintaining safe cooling. You may recall the postcript for the SS300 PSU review that Seasonic's avowed goal for their next gen PSU is, first and foremost, higher efficiency (75%). So many other good things flow out of that. Higher efficiency tends to be the quality PSU maker's holy grail.

powergyoza · Post by **powergyoza** » Fri Jan 10, 2003 11:21 am

sgtpokey wrote:Is this what the efficiency rating means or does the efficiency rating mean something else?

Here's my understanding of "efficiency". If you look at the spec's for power supplies, you'll find two efficiency ratings. One for PFC and one that's normally just called "efficiency". IMO, you can't use either to judge how noisy a powersupply will be.

Like others have said in this thread PFC "efficiency" is a measure of how well the AC is transfered from the power company to your PSU. I won't repeat the other stuff that has been said, but I can give you this situation. Imagine your CPU is connected to a UPS to protect your CPU from surges, blackouts, etc. During a blackout, a computer with Active PFC will drain the battery less quickly than one with Passive PFC. Y? Because Active PFC power supplies are more efficient (usually 90-95%) at handling the power from your UPS. Passive PFC will usually get you about 65%-75%.

The other kind of efficiency measures how well the AC (once at the power supply) is delievered to the electronics. As was already said, the wasted power is converted to heat.

TerryW · Post by **TerryW** » Fri Jan 10, 2003 3:37 pm

Active PFC??

I always though that meant Private First Class!

Snicker-snicker

TerryW

Hebrews126 · Post by **Hebrews126** » Wed Feb 05, 2003 11:02 am

PFC is a way to reduce electrical pollution, known as harmonics, and improve total energy utilization. The reduction of harmonics aids in minimizing interference to other sensitive electronic equipment. Plus, you can possibly save some money on your electric bill with high PF. EN 61000-3-2 is the current standard on Electromagnetic Compatibility (EMC) limits for harmonic current emissions in conjunction with amendments A1 and A2. In the USA, there are no regulatory immunity requirements.

Advantages to having Active PFC with your PSU due to design:
-designed by an advanced IC without coil whine noise and with low frequency coil vibration.
-comes with full range 100V~240V (covers the entire spectrum, not just one or the other) and, thus, eliminates manual switching errors.