Variable voltage (hi & low voltage as possible)regulator/psu from a 12v DC PSU

Discussion in 'The Projects Forum' started by RogueRose, Sep 14, 2015.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
    In another thread I am on a desktop hub/docking station that has all kinds of goodies in it, one is a 3.3, 5 and 12v output as well as a variable voltage output.

    I can easily get power for the 3.3, 5, & 12v from the computer PSU as it puts out 750w and it uses about 20% or so. I also have a very nice, small 1200w (960w @ 120vac) PSU from a server that was pretty pricey when it came out (it's not a cheap, over-rated knockoff).

    What I need assistance with is planning my variable voltage regulator which I would assume would be run from the 1200w PSU. I've seen some of these devices that claim to deliver 5-10 A with a voltage range of ~1.2-37v. I'm not super worried about the voltage range, but the wider the better as well as amperage (higher better).

    Is this something that can be designed and built with a bit of elbow grease? I'm not afraid of puttin in time to do this (PCB design and such), but I'd like to know what kind of voltage range I can expect as well as amperage that is possible.

    Am I correct in thinking that it would be better to have a higher voltage DC input for the variable voltage rather than the 12v? Such as 36, 60 or 72v? From what I've read many of these IC's max input voltage varies from 30-38v.

    So, can anyone give me a general idea of where to start with this? a LM338 seems like it might be a little small but I can run them in parallel, yes? Are there better IC's that offer higher amperage and voltage?
  2. #12


    Nov 30, 2010
    Not likely. You have to know what you need to plan a regulator design, and we can't tell from here. After you know what you need, instead of guessing, "36, 60 or 72v?" the design can start. After you decide on the limits and the features, draw a schematic of what you think you need and people here will help sort out the mistakes. Waiting for a completed design to be handed to you, based on guesses, will take a very long time.
    RogueRose likes this.
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    Start with the loads. They define everything.

    1. What are the output voltages?
    2. What are the peak and average current requirements for each output voltage?
    3. Do the output voltages need to be isolated from the DC input voltage?
    4. Is there room for a cooling fan?
    5. Are there any special requirements (extra low noise, current limiting, etc.)?

    RogueRose likes this.