Forgive me for asking an interdisciplinary question.

I need to get more 5v power out of a desktop power supply to power a bunch of peripherals.

These supplies can go as high as 1600w but the power is mostly only 12v. For example, 1200w available to 12v rails but only 150w to the 5v.

I had this dumb idea. Can we get more 5v power out of motherboard?

Does it typically use something like a buck converter to feed the USB ports (internal and on the PICE) or are they wired to, and thus limited by, the PSU's 5v rails?

  • \$\begingroup\$ A motherboard has many parallel synchronous supplies to get 3.3 volt and 1.35 volts at hundreds of amps. 5 volts is normally direct from the main power supply at 20 to 30 amps. No free lunch on this one. All supplies share a common ground at the main supply. You cannot safely parallel non-synchronous power supplies to get hundreds of amps. Google for what you need and just buy it. \$\endgroup\$
    – user105652
    Mar 28, 2019 at 3:50
  • \$\begingroup\$ 30A on 5V is not enough? What are the peripherals? Normally the feed-forward converters regulate off 5V while the others are tracking by high mutual coupling of each secondary. I agree you are better off getting a separate ACDC supply \$\endgroup\$ Mar 28, 2019 at 3:50
  • \$\begingroup\$ Meanwell make 100A 5V supplies (trcelectronics.com/View/Mean-Well/SE-600-5.shtml). You just need to organize a remote start, and feedback to the PowerOk signal. 2 supplies gets you 1kW of power, but distributing it should be fun. \$\endgroup\$ Mar 28, 2019 at 4:17
  • \$\begingroup\$ @Sparky256 Well, I can't seem to find a standard form factor PSU that supplies more than 30 A @ 5V. Its for a bunch of drives that are getting messed up during spin up. When I attach a 2nd PSU the issue goes away, but I can't fit a second PSU in the chassis. Anyways, you might have the right answer to my question. \$\endgroup\$
    – Mikhail
    Mar 28, 2019 at 4:17
  • \$\begingroup\$ A PSU for a desktop PC or workstation is a complex beast. Not a DIY project even for an experienced design engineer. Also custom boards in small quantities are very expensive. My original suggestion still stands. \$\endgroup\$
    – user105652
    Mar 28, 2019 at 4:57

1 Answer 1


The ~120 - 150W limit on +5V rail in desktop ATX12V power supplies is dictated by economy - it is difficult to find cheap rectifiers with > 30A current.

But you might find plenty of power on 12V rail. Since your load is distributed over "a bunch of 5V devices", you can use distributed converters. What you can do is to use (make) a bunch of in-line DC-DC converters to convert 12 V into 5V, one per each of your 5-V devices, or whatever your load is. The converters can be encapsulated and are easily available with 3-5-10A load capacity. Something like this one,

enter image description here

This should solve the problem of insufficient 5 V power.

  • \$\begingroup\$ Yeah, I was thinking of doing something like this. Guess this question is one of those XY problems. Although the original question wasn't that bad :-) \$\endgroup\$
    – Mikhail
    Mar 28, 2019 at 6:24
  • \$\begingroup\$ @Misha, which XY? You do have a "bunch of peripherals", don't you? If you mean a bunch of PCIe USB controllers, then it depends, some are using raw +5V, some have 12V-5V embedded converters with power from an auxillary connector, and won't supply VBUS unless you plug the Molex 4-pin or SATA power connector. \$\endgroup\$ Mar 28, 2019 at 6:40

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