After reading all the forums and researching on the internet here's what I understand about Active/Passive PFC, please let me know if I am right or wrong about any of the following points:

1. PFC is not the same as efficiency. There could be two PSU with 65% efficiency, but one with 75% PFC and another with 99% PFC.

2. Active PFC PSU run more efficiently in drawing power from the Hydro company. So, the better the PFC, the less the power consumption resulting in smaller hydro bill. (not too sure about this since this kinda contradicts the first point)

3. Active PFC's are more efficient, so they run cooler and are easier to cool down.

4. PFC got nothing to do with more or less power. Meaning that two identically rates PSU with and without actice PFC would deliver the same power.

5. Efficiency: non-PFC < Passive PFC < Active PFC

6. Active PFC is preferrable PSU.

Now, having said all that. I have also seen some contradicting posts in the forums. For instance, Seasonic Passive PFC seems to be quieter since it uses a less powerful fan (but why?) . Also, some said to buy a passive PFC since it's easier to cool with low flow fans. So, either I am missing something here or those posts were not accurate.

Lastly, are Fortron's passive or active PFC?

Anyone want to clarify?

I think there's some mix between*
A. the power factor : ratio between active and reactive power
B. the efficiency of the core transformation (AC -> DC) process
C. the efficiency of the PSU as a whole big (black) box

In any case, it's better for your electricity network and for environment to use PFC PSU

* Not in your points, but more in general.

>1. PFC is not the same as efficiency. There could be two
>PSUs with 65% efficiency, but one with 75% PFC and
>another with 99% PFC.

Right. Here 'efficiency' refers to the AC-DC conversion efficiency of the power supply. A 65% efficiency would mean that 65% of input power is converted to output power and the rest is generated as heat (and perhaps some noise / magnetic emissions).


>2. Active PFC PSU run more efficiently in drawing power
>from the Hydro company. So, the better the PFC, the less
>the power consumption resulting in smaller hydro bill. (not
>too sure about this since this kinda contradicts the first
>point)

Right. PFC avoids harmonic distortion load on the electricity transmission lines which results in reducedheat generation in transmission equipment, reduced likelyhood of broken transmission equipment and increased overall power transimission efficiency.

It's good for the utility company and at least in some parts of the world the utility companies charge you for the power you use AND the harmonics you produce. Hence, better the PFC the less one pays to one's utility company.

In EU the demands for a PFC supply of 300W or more power are such that practically all ATX PC PSUs sold here should be Active PFC. However, that doesn't seem to be the case yet. This puzzles me, but so do many other things regarding EU

>3. Active PFC's are more efficient, so they run cooler and
>are easier to cool down.

This is true when compared to a particular passive PFC design. I'm not 100% sure about this when compared to a non-PFC design. I'm now talking only about the efficiency of the PSU, not the efficiency of the electricity transmission down the lines.

My layman thinking would guess that a APFC PSU would probably be slightly less efficient (as a PSU) than a NON-PFC PSU, due to the APFC circuit power needs.

However, this is probably more of an implementation issue as one can make a really bad active PFC PSU and a good passive PFC PSU. It's mostly in the design.

Perhaps somebody who has more understanding about PSU design could chime in?

>4. PFC got nothing to do with more or less power.
>Meaning that two identically rates PSU with and without
>actice PFC would deliver the same power.

In theory yes, in practise it may depend on some factors. If the designs were identical sans the APFC circuitry, then probably for all practical purposes the answer would yes (I'm not totally sure, I'm not an expert on this).

However, as the PFC circuitry may change how the PSU operates in under-voltage conditions, the performance might not perhaps be the same on a really bad line (i.e. problems with the utility company). Again, guessing here.

>5. Efficiency: non-PFC < Passive PFC < Active PFC

For PSU efficiency, I'd guess that the theoretical (best of design) order would be:

non-PFC > active pfc > passive pfc

However, I believe the PSU efficiency is probably more the function of it's design and implementation rather than whether it's a PFC unit or not.

For transmission efficiency the chart is more than likely as you describe above.

>6. Active PFC is preferrable PSU.

Over a passive PFC PSU (higher PSU efficiency, less heat, less likelihood for additional conversion noises, better use of transmission power): Yes

Over a non-PFC one (higher transmission efficiency for your utility company, perhaps smaller bills for you, good for the environment): Yes

That's my take on things, but there are special situations where a passive PFC or a non-pfc unit might be better.

For a general home PC use I'd recommend A PFC as the best solution though if all other variables remain almost constant (i.e. heat/noise/price/etc).

regards,
Halcyon

Halcyon has got it all, pretty much. His last point -- APFC is best -- is right, AFAIK. Just a few confirmations & observations:

A. No connection between AC/DC efficiency vs Power Factor.

B. PF = power factor. PFC= power factor correction. You get high PF by implementing PFC, and ActivePFC is a more efficient way to implement PFC than Passive.

C. Internal heat relates only to AC/DC efficiency AFAIK.

D. One simple definition of PF is the difference between watts and VA (Voltage X Amps). This is exactly how the Kill-A-Watt device seems to calculate PF -- it is W divided by VA. The best it can be is 1. With low PF devices, VA is much higher than watts; with ActivePFC PSUs, it's only just a wee bit higher, and PF is typically 0.95 or better.

E. PF does not stay the same at all power levels, even with Active PFC. It seems to go up as power output increases. With passive PFC, I have seen 10~20% changes. Much less variation with APFC.

Thanks Mike! Many useful points I didn't know.

I also need to clarify one point which I left a little vague in my original post

APFC PSUs can often be more efficient (the AC/DC conversion) than many passive PFC PSUs due to the design and components used on the passive PFC. This increased efficiency (which probably isn't that much) results in less heat generated than on the active PFC PSU.

So, most of the times active PFC units are more efficient in power conversion (AC/DC - internal efficiency) and power correction than passive PFC units.

regards,
Halcyon

So would a PC with a APFC PSU will last longer on a UPS than an identical PC with a non-PFC PSU? (for sake of comparision, lets say the PSUs are both made by the same company, same rating,etc)

Since the electricity is included in our monthly Condo maintence fees, this is the only reason I could think of where I would immediately realize a benefit of using a APFC psu..

Don't think it is possible to generalize like that. Besides, don't you think reduced energy consumption for ecology's sake is worthwhile, even if it is just a drop in the bucket? Many drops fill the bucket...

Don't get me wrong, I don't use that as an excuse to waste energy.. Having said that, I'm am not going to go out and spend money replacing something that works perfectly, just for the sake of a slight reduction in energy consumption..

So let's apply all this to a real-world buying decision:

I noticed yesterday that silenX psu's at silenx.com come in two varieties for the 300W and 350W models - the regular ones and a new IxtremA model (which has an Active PFC Circuit, I guess the regular is passive?). Whereas the regular 300w costs $65, the new IxtremA costs $70 ($85/$90 for the 350's) . The only differences I see in their listed specs are:

http://www.silenx.com/viewPrd.asp?idcat ... dproduct=2
regular:
Input: 115/230V @ 50/60 Hz
Efficiency: 70% under load

http://www.silenx.com/viewPrd.asp?idcat ... roduct=153
IxtremA:
Input: 95~265V @ 50~60 Hz
Efficiency: 74% under load

the IxtremA models also list 'Power Factor: 99%' under their specs, whereas the regulars don't mention Power Factor. And under the 'Features' section, whereas the regulars describe 'Advanced power load based fan control circuitry', the IxtremA's describe 'Advanced temperature/power load based fan control circuitry'

Is there enough benefit from the Active PFC model in the expert opinions here to make it worth the extra $5?

I don't know anything about that new PSU, but yes the xtra $5 is well worth it. If your electricity provider charges for harmonics, you'll easily save that amount over the life of the PSU (most likely several times over). Moreover, you'll never risk frying your PSU, should you travel between 120 & 230 volt countries.