PSUs 101: A Detailed Look Into Power Supplies

References
By Aris Mpitziopoulos
last updated

The objective of this article is to provide detailed information about the most crucial part of a personal computer (PC) system, its power supply unit. Follow us on this journey into PSU territory and we promise that you will gain valuable knowledge.

Digitally Controlled PSUs

Several PSU manufacturers recently started using digital control circuits alongside analog circuits in their implementations. The crucial advantages of digital controllers are, first, their ability to consider many more factors, and second, the increased speeds at which all data is processed. They are able to provide very high performance with increased efficiency levels and almost perfect load regulation, as well as low ripple levels. In addition, it's possible to adjust the voltage levels on the rails that are digitally controlled.

Another crucial benefit of digital control circuits is that they easily allow the monitoring and control of the PSU through software. So far, the unit with the highest overall performance score on our charts is a digital PSU, which clearly shows the performance improvement over PSUs that use analog circuits. Nonetheless, analog circuits will continue to be used in PSUs for quite a long time, as they have proven to be reliable and, more important, their cost is significantly lower. And with all of the knowledge gathered so far, analog circuits can still offer high performance levels.

Image 1 of 4

The PCB and the control PCB of the Corsair AX1500i.

Currently, there are no purely digital PSU platforms available. Even in the most advanced implementations, some parts (like the 5VSB regulation circuit, the DC-DC converters that generate the minor rails or the APFC stage) are still controlled by analog circuits. As the use of digital circuits becomes more common among PSU manufacturers, however, we believe that fully digital units will become available, offering new levels of performance under all conditions.

Through their software interfaces, digital PSUs also provide lots of useful information on the function and performance of PSUs, along with interesting control options. We will have to wait until this technology matures and the production lines adopt digital circuits on a wider scale to see the prices of digital PSUs at more reasonable levels.

Before we end this section, we would like to stress that all digital PSUs use, and will continue to use, the topologies mentioned in the previous section. The only thing that will change is that the control will be done by processors and not by analog controllers.

In the above scheme, the block diagram of the Corsair AX1200i digital unit is depicted. As you can see, in addition to the primary digital signal processor, there are two secondary microcontrollers (MCUs), with one of them handling the communications interface and the other controlling various circuits in the PSU's secondary side.

Aris Mpitziopoulos
Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.

42 Comments Comment from the forums
  • Alexis Shaw
    In your list of top-tier capacitor manufacturers you missed out on some of the better american and european manufacturers, while these may not be used on many consumer-grade power supplies they are definitely top-tier and if you were to find them you would be happy. I suggest the addition of at least:
    Cornell Dubilier (USA)
    Illinois Capacitor (Now owned my Cornell Dubilier)
    Kemet Corporation (USA)
    ELNA (Japan)
    EPCOS (TDK company) (Germany)
    Vishay (USA)
    Würth Elektronik (Germany)
    Reply
  • Aris_Mp
    Thank you very much for the list you provided. I am aware of almost all cap brands that you mentioned but unfortunately so far I found none of them inside a desktop/consumer grade PSU. I will think about it however (and also make a research on these cap brands), if I should include them as well inside my list.

    Reply
  • InvalidError
    16585466 said:
    Thank you very much for the list you provided. I am aware of almost all cap brands that you mentioned but unfortunately so far I found none of them inside a desktop/consumer grade PSU.
    There is a very high probability you have seen PSUs with several Kemet capacitors in them. You never noticed them simply because SMD capacitors are too small to carry logos, brand name or even value designations.

    The other brands are mostly found in specialty applications such as lab instruments, industrial machines and high-end audio.
    Reply
  • Math Geek
    very interesting read. more in depth than i need to know yet for the most part understandable and with careful reading it did not leave me confused.

    nice article.
    Reply
  • TallestJon96
    I only read 2/3 of it, but it's a good article.

    I basically have committed PC heresy with my cx600m. However I think that I'm in the clear with my 65w CPU and 145w CPU. I'd bet my total power draw is actually below 300w, the supposed highest efficiency point of a PSU.

    As a gamer, not a professional, I think it is better to get low power parts, and get a higher rating than you need, rather than get high power parts and high quality PSUs.

    Additionally, if you compare power consumption of a typical system from today to one from 5 years ago, power draw is considerably lower, with the exception of certain graphics cards. *cough* 390x *cough*
    Reply
  • powernod
    I decided to sign up at Tom's forum, and the only reason was to state how excellent is Aris's article!!!
    Thanks Aris for this very useful article on behalf of us all who want to learn the basic knowledge for PSUs.
    Haven't finished it yet, but i'm very anxious for it !!!
    Reply
  • GoZFast
    Very nice article!!! You made me remember my college physics courses lol
    Reply
  • traumadisaster
    I'm glad there are people dedicated to this but I'm not. I can't even read all of the chapter titles in this article. I disagree with the importance you place on this and all of the references you made to this being crucial knowledge.

    PSU and MB are insignificant to me and I can blindly pick one by reviewing user comments from newegg in about 5 min, and it will last for years. For less than $100 each I'm set for nearly a decade.

    CPU and gfx card now that affects fps and is over $1000, actually the most important part to me.
    Reply
  • Alexis Shaw
    16589602 said:
    I'm glad there are people dedicated to this but I'm not. I can't even read all of the chapter titles in this article. I disagree with the importance you place on this and all of the references you made to this being crucial knowledge.

    PSU and MB are insignificant to me and I can blindly pick one by reviewing user comments from newegg in about 5 min, and it will last for years. For less than $100 each I'm set for nearly a decade.

    CPU and gfx card now that affects fps and is over $1000, actually the most important part to me.

    I heartily dissagree, user are not the best way to judge reliability, and a bad powersupply is at fult most of the time there is a hardware issue. Further a power supply should last more than one system build, and in general I keep mine for a decade at a time at least. So an investment in a good power supply is not a waste, and a bad one will kill that precious $1000 GPU or CPU. The demo dart power supply on the motherboard is a similar story, however in general they are of higher quality than a cheap mains supply.

    Reply
  • Alexis Shaw
    16585679 said:
    16585466 said:
    Thank you very much for the list you provided. I am aware of almost all cap brands that you mentioned but unfortunately so far I found none of them inside a desktop/consumer grade PSU.
    There is a very high probability you have seen PSUs with several Kemet capacitors in them. You never noticed them simply because SMD capacitors are too small to carry logos, brand name or even value designations.

    The other brands are mostly found in specialty applications such as lab instruments, industrial machines and high-end audio.

    As well as SMT ceramic capacitors, Kemet makes through hole aluminium electrolytic capacitors. These are of high quality, though not as well known as their SMT capacitors. They also make high quality polymer SMT capacitors that are used as bulk capacitors on the power distribution circuitry on laptops and other devices.
    Reply