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The AC receptacle is the socket where you connect the power cable at, often accompanied by a simple on/off switch. The switch does nothing more than isolating the power supply from the power grid by interrupting the live wire.
On older power supplies you could find an AC voltage selection switch which had to be set to comply with the utility grid voltage (110V or 220V) depending on where you live at. This is no longer necessary because newer units automatically sense the grid voltage through the active PFC circuit. Since the installation of an active PFC circuit became obligatory by law in many of the world's countries, it is highly unlikely you will find a passive PFC unit (or a unit without a PFC circuit at all) being sold today.
The first thing the power supply has to do is make sure that the AC power is as clean as possible. That includes both the AC power the power supply is receiving but also the AC line itself; switching power supplies generate harmonics which must be filtered before entering the AC power grid. This is done by implementing a transient filter circuit.
The transient filter usually consists of capacitors and induction coils and sometimes includes a metal-oxide varistor (commonly known as a MOV) and a simple glass fuse for extra protection. We say “usually” and “sometimes” because there are no restrictions concerning what manufacturers can and cannot use. High quality units try to meet and exceed the ATX specification guidelines. Very poor quality units will probably have no transient filter at all, so they will flood your household power grid with electrical noise and can be seriously damaged even by a slight power surge.
The most common transient filter components are:
- Y type capacitors : Used for line bypass, connected between Live or Neutral to Ground. They are used in applications where capacitor damage may lead to electric shock and they shunt current to Ground.
- X type capacitors : X type capacitors are being used across the lines, connecting Live to Neutral. They are used where damage to the capacitor cannot induce electric shock and also operate as fire retardants.
- Induction common mode (filtering) coils : Common mode choke coils are used to suppress common mode noise (EMI/RFI filtering). This type of coil is produced by winding the signal or supply wires one ferrite core. Since magnetic flux flows inside the ferrite core, common mode choke coils work as an inductor against common mode current. Accordingly, using a common mode choke coil provides larger impedance against common mode current and is more effective for common mode noise suppression than using several normal inductors.
- Metal Oxide Varistor (MOV) : Metal oxide varistors (MOVs) are semiconductors that protect electronic components and systems from transient voltages. Their design allows current to flow in only one direction. MOVs have very high resistance at low voltage and very low resistance at high voltage, which is where their name comes from (Variable Resistor). Thus applying low to moderate voltage has little to no effect, however a high voltage triggers an “avalanche effect” and causes the diode to break down. In short, these very little components are your typical, reliable surge suppressor. MOVs tend to degrade if they are repeatedly exposed to transients.
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