Do I need PFC in my power supply?
- Thread starter erwin1978
- Start date
Active Power Factor Correction is only in very specific conditions going to be of any value to an end-user. Some of these include:
1. You have very dirty power.
2. You are a business and get charged by the power company for drifting away from 100% PF.
It's not a bad thing, per se, it just doesn't really offer you any particular advantages. It is a nice thing to do for the power company, as it makes their job a little easier, which I suppose in aggregate could save you a little money over the very long term.
Some thoughts on active PFC.
1. You have very dirty power.
2. You are a business and get charged by the power company for drifting away from 100% PF.
It's not a bad thing, per se, it just doesn't really offer you any particular advantages. It is a nice thing to do for the power company, as it makes their job a little easier, which I suppose in aggregate could save you a little money over the very long term.
Some thoughts on active PFC.
If you want maximum efficiency - then bear in mind PSUs can only be made with maximum efficiency with active PFC (not all active PFC PSUs are designed this way. Passive PFC doesn't help efficiency).
Other than this rather tenuous benefit, it doesn't help much for domestic users. (Industrial users may pay extra for uncorrected power factor.)
Possibly, if you have dirty power it may help, as active PFC stabilises the voltage before it gets to the main PSU itself (again, this benefit is unique to active PFC - passive PFC doesn't do this).
Active PFC is often promoted as a high-end feature. So, for this reason alone, a PFC supply may be a better product (higher end parts, better design, etc.)
Other than this rather tenuous benefit, it doesn't help much for domestic users. (Industrial users may pay extra for uncorrected power factor.)
Possibly, if you have dirty power it may help, as active PFC stabilises the voltage before it gets to the main PSU itself (again, this benefit is unique to active PFC - passive PFC doesn't do this).
Active PFC is often promoted as a high-end feature. So, for this reason alone, a PFC supply may be a better product (higher end parts, better design, etc.)
You don't need it if you're not in the EU (it's a requirement here) but most of the good ones have it anyway.
Better to pay a few extra dollars for it since it generally implies superior overall quality, unlike the same spent on paint and lights.
thecoolnessrune
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- Jun 8, 2005
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Active PFC definitely helps in my area since we have have fairly bad power here. (Old home, bad wiring) Also, a feature of them is that you dont have to switch between 120V and 240V. (Its done automatically instead of via switch). So if you trave to different countries alot. It can be a nice help.
Maximum efficiency is NOT dependent on PFC!!! Under ideal condition, the use of PFC will do nothing for efficiency. Most of the time, PFC will reduce system efficiency by a very small amount. Again, we are talking about residential customers in the US.
It depends on how you look at it.
PFC doesn?t do anything to help the AC to DC conversion, so in that sense it doesn?t do any good. The benefit of APFC is that it consumes or wastes less power on the AC grid. Basically it comes down to apparent vs. real power; you can get a good description of it in this Wikipedia write up.
Active PFC will increase efficiency. It reduces the amount of reactive (inductive/capacitive) power generated by the PSU. This is a good thing for you, because the power company bills you for apparent power usage (apparent^2 = real^2 + reactive^2). If you remove the reactive power usage, your real power usage will not change, but your apparent power usage will fall, so you will be charged less by the electricity company.
RoD
Agreed with the exception of the bolded text, the real power useage increases because of the PFC (active or passive both will have losses), maybe not much at all but there will be some. If they are billing you for apparent power then maybe the power bill will be less, but overall it's less efficent.
OK, the APFC will slightly increase real power usage, but this will be more than outweighed by the reduction in reactive power. No offense, but I've studied this stuff at uni, (I'm doing ECE) and I'm pretty confident my lecturer knows what he's talking about.
RoD
Then he should know that power companies bill for real power, not apparent power. Reactive power has an essentially trivial direct impact on home power bills (it would be zero, but being off unity power factor does increase heat dissipation a bit). It's pretty much free- because hey, you give it right back!
There's a case to be made that moving closer to unity (and closer to a pure sinusoid) reduces costs for the power company (again, heat), and thus your bill. But directly, the impact is inconsequential.
Computer power supplies are overall inductive loads, as most off-unity devices people use are. They absorb reactive power, and don't generate it (capacitors do). And as stated, you are not billed based on apparent power in a residential setting.
That is true.
However, you can significantly improve the DC-DC conversion circuit, if you have active PFC.
A major source of inefficiency in a conventional PC PSU is core losses in the main transformer. The core has to be significantly oversized in order to compensate for voltage surges/sags in the mains and ripple from the reservoir capacitors. Since energy losses are proportional to volume, this means voltage regulating ability has to be traded against efficiency.
An Active PFC circuit is a voltage regulator (specifically it's a boost DC-DC converter - modified with a 2nd feedback loop to control the power factor). Because the active PFC circuit supplies tightly regulated DC - an optimal sized main transformer can be specified, instead of an oversized 'safe' transformer - this can signficiantly improve efficiency.
It's important to recognise that the aPFC alone doesn't give you the improved efficiency. There has to be a specific redesign, which takes advantage of the aPFC.
Early adopters of aPFC (e.g. Channel Well Tech, and associated rebadgers like Antec) simply bolted an aPFC module onto the front of existing designs. In this case, there was no improvement in efficiency (and possibly reduced efficiency due to the power required by the aPFC). However, where the PSUs have been redesigned, significant improvements in efficiency are possible.
Actually, they're neither inductive nor capacitative. They're non-linear, meaning they tend to generate harmonic reactive power. Cleaning up the harmonics is significantly more difficult than simple reactive power (it requires multiple inductors and capacitors).
No offense taken at all, i'm studying it now, and while your lecturer might know what he's on about that doesn't mean that you got it right (ironic as technically you didn't
)Reactive power is not real power, think of it as borrowed power. Some power companies charge for this as it tends to mess up their grids, but it is not the same as making it more efficent.
Again, a PFC circuit will consume SOME power. There ain't no free lunch. A well designed PSU without PFC will ALWAYS be MORE efficient than one with PFC.
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