Passive PFC

[Pentium4]

Never really learned much about PFC so I want to start with the basics...Can Passive PFC have any effect on how much power the PSU can output? Can the higher PF increase the efficiency at which the bridge rectifies the current or is that solely based on the output rectifiers?

I thought PFC was just to reduce the extra noise that a regular input filter can't get rid of, preventing less interference on the mains voltage. For a regular old PSU with the spot for it on the PCB can you just solder on a PPFC coil and call it good or is it completely integrated into the design of the PSU?

[Wester547]

Re: Passive PFC

Passive PFC improves upon "power factor" - the amount of power the power grid thinks you're using, which is different than the amount of power you're actually drawing from the mains. It does result in more heat losses and often I see it implemented in such a way that it might impede airflow to the parts of the PSU - it is heavy and often a huge inductor. What it also helps though is the possibly high (or compromising) currents in the AC waveform/line voltage by way of many computers drawing high peaks, but Active PFC works to the same effect. It -might- also reduce or at least smooth the peak currents and spikes in the transformer and maybe some of the other components, but I could be wrong on that. I personally prefer PSUs without Passive PFC to maximize the amount or airflow available.

[Pentium4]

Re: Passive PFC

Oh interesting...They do tend to block a lot of airflow. Seems pretty pointless then, might as well have Passive or none at all

[Pentium4]

Re: Passive PFC

I meant "might as well have Active PFC or none at all" whoops

[Wester547]

Re: Passive PFC

Active PFC can be a problem as well depending on the brands used because the primary capacitors are quite a bit more stressed and in some designs that are crappy enough the APFC coil (if cheap enough) runs so hot that it tends to fry everything around it, including itself (a badly enough designed APFC circuit can run hot enough to kill Panasonic primaries), though if the APFC transistors aren't hot they should be okay. There are advantages, such as better use of the power grid and not having to worry about the voltage selector, and the higher voltage and frequency of the whole circuit (the more sinusoidal current means less AC ripple but of course the higher voltage still means more stress...), which helps (though the heat losses of Passive PFC are actually less, so it's more efficient in power factor).... but I personally prefer the simplicity and less stress of the voltage doubler + more airflow for all the components, and not only that but more room for airflow to exhaust heat out of the computer as a whole (or rather extra means to do that besides possible case fan[s]).

[severach]

Re: Passive PFC

80Plus ends all that. There's no way a power supply burning up Panasonic capacitors can snag an 80Plus certification. My 80Plus Gold supplies don't have many places they can leak heat.