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As we mentioned in the operation principles of switching power supplies, the first thing it has to do in order to transform the utility grid AC voltage to DC is rectify the cleaned AC voltage to high voltage DC. This is done through a single chip, called the rectifying bridge, which is assisted by a number of large electrolytic capacitors (usually 1). It may or may not be connected to a heatsink, depending on the class and power output of the power supply.
The power factor correction (PFC) is also taking place at this part of the circuit. Switching power supplies are highly reactive power loads and will cause a huge current-voltage phase shift while operating, drawing a lot of useless reactive power along with the necessary active power. The PFC circuit controls the input current of the power supply and is trying to nullify the phase shift between the current and voltage.
A power supply without power factor correction usually has a power factor of 0.5, meaning that it may draw as much reactive power as active power altogether. An active PFC circuit will bring the power factor very close to 1, nullifying the reactive power draw almost completely.
The power factor will not increase the actual performance of the power supply itself directly, neither will decrease the consumption of power which home users pay for. Large businesses and industrial buildings are being billed for the amount of complex power they use, which includes the reactive power, and are fined by the utility company if the power factor is too low. Home users are being billed only for the amount of active power they use. But it is a huge mistake to believe that just because the home users are not getting billed for the amount reactive power they consume, there are no advantages at all.
The power factor is an efficiency figure, indicating how efficiently an electrical load can draw and make use of utility grid power. Despite that home users do not have to pay for the reactive power their equipment is drawing, their entire household electrical grid has to be sized according to the complex power they use. This includes wiring, safety equipment and UPS systems. In short, a power supply without a power factor correction circuit not only will strain the entire electrical grid (including that of the household) for no reason, but when purchasing an UPS a much larger and far more expensive product is necessary. (For more information, please read our “Why companies rate UPS in VAs and PSUs in Watts” article).
Bloody Nora IronLaw, that certainly is detailed. I made it to page 2, now I need a glass of coke (cola not powder). I shall return later once I absorb the basics !
I am one of the most demanding readers on the face of the planet. The standard of editorial content on this site is without a doubt leading the way on the net right now. Some of the news stories are very ermm interesting, but the reviews are fantastic.
I have bookmarked this, I shall spend a few hours Sunday afternoon chilling and trying to work this out. I need to read this at a snails pace to get to grips with it all.
Well this is taking power supplies to the next level. I got lost in parts, and im quite technical, but its well written and rather complex. Nice idea these articles, at least you guys expect the readers to know more than the usual tech site reader
Thank you, thank you , thank you.; I always wanted something like this, with images and easy to understand text. I have struggled on page 4 and 5, but I have picked up more from this than any other PSU related article on the net.
A hell of a lot of work in this Ironlaw. Thank you very much for making all this effort to educate us peasant mortals π
brain overload………… ekkk.
I am just too stupid to understand half of this, but thanks anyway ! the last page was as far as I made in understanding it all :p
Stunning work IronLaw, technically way above my level, but I feel a little better for having read it. I love the PSU reviews on KitGuru too. at the same level as Hardocps (which are also excellent).
With standard of content like this on a regular basis, you will go far ! top marks KG
Christ on a stick. lost for words. This is more for apprentice engineers !
Normally I see these guides and think, oh here we go again, some idiot reviewer ranting on about something stupid and trying to understand it himself.
Not in this case. Ironlaw is a cut above! really really enjoyed this one.
**claps** – I understood most of it, which is surprising as I only know the basics about power supplies. I hope to see more of these. I would like one explaining what exactly we need to buy when looking for a PSU, single rail 12v? multiple rails. and making sense of actual ratings. who needs 1200W psus for instance? do we ?!
Well that was surprising. very very good reading. bit complex for me in parts, but I picked up bits and pieces.
Ironlaw, thank you. very informative reading for a friday morning π now off to work to type in numbers.
lol, I just read something so badly written on bittech, then I come here to read this. its like comparing nickelodean to the discovery channel.
I feel educated, thank you π
For such a complex article it is very informative, a little complex for this geek, but im sure many people love all this about PSU’s. The last page was helpful :p
I shall email Zardon for permission to use parts of this for an edu guide I am writing for college kids.
Brilliant piece of work. 10/10
I find power supplies totally confusing. I just buy one and get a good one after reading several reviews online. I actually ordered the thermaltake one after reading the review on kitguru. This was educational but honestly a little over my head for 70 percent of it. I learned a little, which is more than I normally do every day !
Fantastic writing and very educational as other people have said. I read the power supplies reviews here in the last month and I prefer them to johnny guru. Johnny is great with PSUs but his writing style annoys me, jokes are fine, but half the review is him trying to be funny. The reviews on this site are just as detailed but more focused. I hope you get the corsair 1200w PSU to review, I want to order it, but its 260 here and im not sure if its worth it.
read it in detail – very good work indeed Ironlaw, you know your work π
My brain hurts.
Where do i find the for dummies version?
Nice work mate π
Cool and easy to understand