KitGuru KitGuru.net – Tech News | Hardware News | Hardware Reviews | IOS | Mobile | Gaming | Graphics Cards
Even though there are more than eight types of power supplies, for household and business equipment there are only two basic power supply designs, linear and switching power supplies.
Linear power supply units are relatively simple and common for low power applications. They fundamentally work by stepping down the AC voltage of the utility power grid, rectify it to DC voltage and finally filter it by using a capacitor.
In order to step the voltage from the 90-240V utility grid voltage down to a low voltage usable by the equipment, linear power supplies use a transformer. The transformer steps down the supplied AC voltage to a lower value (e.g. 18 VAC) but the original waveform remains unchanged. Then a rectifier is used to transform the sine wave AC voltage into a fully rectified pulse voltage. As this rectified voltage still resembles AC, it cannot be used yet. Filtering through a capacitor is required to transform this voltage to near-DC. Then a voltage regulation stage is necessary to adjust this near-DC voltage to true DC voltage and sustain it regardless of changes in the load current.
In very small and simple applications that can be done by using a Zener diode but most of the time a full voltage regulation circuit using a power transistor operating in its linear region is necessary. This power transistor has the ability to act as a variable resistor in series with the load, regulating the output current and voltage accordingly. It is controlled from a circuit sensing the output voltage and modifies the transistor bias to maintain a set voltage output despite of any load current changes.
Linear power supplies have many desirable characteristics. They are very easy and cheap to manufacture because of the few and common components, which also makes them very reliable when correctly designed. Their performance is excellent as well, with exceptional output voltage regulation and next to non-existent ripple. Finally even the lowest quality products show very little electromagnetic interference (EMI) and exceptionally fast response times.
With so many advantages people would expect linear power supplies to dominate today's technology market, yet that is not possible because of their two main disadvantages. Even though linear power supplies are simple and easy to manufacture, they are only used for simple and low power applications because their size and weight increases dramatically as their power output increases.
This primarily has to do with the input voltage frequency, as we will later explain. Early linear power supplies for electronic equipment would not output more than 10A, yet still they used to weight more than 10kg and had electrolytic capacitors as large as coke cans. Linear power supplies are also extremely inefficient, with even the best of products not being able to offer an electrical efficiency higher than 45-50%.
The extremely low efficiency not only is a waste of precious power but it also is a very large heat source which needs to be dealt with by implementing corresponding cooling solutions. Imagine having a small linear power supply powering an office computer; even a 300W power supply with a 50% efficiency would need to dissipate another 300W as heat and would be at least 6 times the size of a common ATX design. These disadvantages make the linear power supplies useless for a wide range of applications. Of course the technology progressed since their first appearance but linear power supplies are still usable only for simple, low power applications such as AC chargers and laboratory power supplies.
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