A simple very-low-noise 5v supply you can build at home

Discussion in 'DIY (Do-It-Yourself) Discussions' started by ericj, Sep 12, 2017.
  1. ericj
    About a year ago i was staring at my gamma 2 DAC and musing that it was really gauche of me to always use it on USB power and input.

    I know that between the LDO regulators intermal to it and the reclocking, it hardly matters. But you know. It's the DIY version of upgraditis.

    I had recently gotten the hang of KiCad so i searched Mouser for an ultra-low-noise regulator that comes in a package that a human being can hand solder.

    I settled on the Exar XRP6272IDBTR-F. It's a power-pad (metal belly) SO-8 device. Fixed 5.0v if you ground the reference pin or adjustable up to 5.0v.

    Internal FET, just needs a few capacitors. They state explicitly that it is designed to work best with monolithic ceramics. The caveat is that it's maximum input voltage is 5.8v.

    Up to 3 amps, allegedly, but i assume that is under ideal conditions with a multilayer board that has a lot of thermal vias. I wanted something i could etch on a single side and install inside a wall-wart.

    So, bridge rectifier made of fast soft recovery rectifiers, filter caps, lm317 set to 5.8v (ish), then the exar chip and it's supporting input, output, and bypass caps. I put pads on the board for a ferrite bead on the output mostly because i needed a top-side jumper if i wanted the power output pad to be at the edge of the board. It's probably not doing anything meaningful.

    I don't know that it achieves "ultra" low noise, but it's at least very low noise. When i finally built one last night, none of my instruments could detect any ripple on the output, compared to the microvolts of ripple I am used to seeing directly out of a 317.

    Just the one surface-mount part. You should be able to get some solder onto the thermal pad by having a small hole under the chip and using a bit of copper wire to wick it down there. I forgot to do this when i built my prototype. I have a hot air system so i could probably pluck the chip off and do it, but the gamma-2 might not load it enough to be an issue, and futzing around with it might kill it. I figure if it dies, I'll replace it and try to do it right. Until then i will just see if it works, and leave well enough alone.

    It should be understood that larger capacitors before or after the exar regulator are not desired and will probably hinder performance.

    Will this improve SQ? ¯\_(ツ)_/¯

    I didn't actually use UF5408 or an lm350 for this build. Use whatever rectifier diode, and a 317.

    Mouser parts:

    701-XRP6272IDBTR-F -- regulator
    810-FK26X7R1C106K -- 10uf 10v mono ceramic
    810-FK26X7R1C475K -- 4.7uf 10v mono ceramic
    594-K223K15X7RF5UH5 -- 22nf mono ceramic

    The rest is less critical. I just used stuff i had on hand.


    Last edited: Sep 12, 2017
    broc3 likes this.

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