Another ATX Power Supply

Discussion in 'The Projects Forum' started by Murizg, Apr 3, 2018.

  1. Murizg

    Thread Starter Member

    Mar 23, 2018
    49
    1
    While I'm waiting for some components to arrive so I can troubleshoot my 0-30V 0,2-3A DIY adjustable power supply, I wanted to make something else. For a while now I'm struggling to get some sort of a variable power supply. Choosing a ATX power supply that I already have seems like a reasonable idea.
    I don't know if it is too much to ask from it to have there features:
    - 3,3V, 5V, 12V and a adjustable 0-24V (I was thinking of putting a buck/boost converter over the 12V rail, I suppose it should be doable?)
    - I would like 2 USB ports
    - I have a Volt/Amp meter that I would like to integrate. Now, is there any way that it can be connected to all rails?
    - I haven't seen that anywhere, but, is there a way to integrate a constant current circuit over the adjustable rail? If so, how complex would that be?

    I'm making a separate enclosure for this project, so the original ATX PSU will stay in its original metal case and will be attached to this enclosure with several bolts. I will provide few photos if anyone will be interested when I get back to my workshop...

    Any other suggestions would be really appreciated.


    Thanks a lot
     
  2. wayneh

    Expert

    Sep 9, 2010
    16,102
    6,219
    Yes, all these things are possible and are not terribly complex.

    I made something similar and incorporated a 4-20mA meter that I had lying around. In my case I used a low ohms (o.1Ω or something like that) shunt resistor between the load and ground. This gave me a voltage I could scale with an op-amp circuit to give 4-20mA from a load current of 0-2A.

    My power supply can operate in either mode, constant voltage with a current limit, or constant current with a voltage limit. You may want to consider if you want that.
     
  3. Murizg

    Thread Starter Member

    Mar 23, 2018
    49
    1
    Hey Wayneh!
    Ahmmmm...
    Well, sounds great!
    So, for a starter, I should buy a StepUp/StepDown converter that has a input voltage anywhere from lets say 5-15V and can output 0-25 or 30V? Then I should connect +12V on it to get variable voltage? I'm not really sure what you meant by 4-20mA meter? Nor how should I get voltages below 0,8V since most converters don't go below that if I understood correctly? Do you happen to have some sort of block diagram or something?
     
  4. wayneh

    Expert

    Sep 9, 2010
    16,102
    6,219
    No, mine was crude and different enough that it wouldn’t help you much.

    A 4-20mA meter is one that takes its power from the current being driven through it. It’s a widely used type because you don’t have to worry about voltage drops. The current is identical in all parts of the loop.

    There are ways to increase the output voltage of an ATX supply. I’d look to do that before adding a boost converter. Maybe you can get all you need without the converter.
     
  5. djb

    Active Member

    May 17, 2008
    31
    3
    If you are still online here, lately i have some experience on your topic. If you are experienced with integrated switchmode controllers you can do step up to get your 30V, and step down to get below 12V, assuming your main voltage supply from ATX would be the yellow line.
    Also you can go custom design with arduino microcontroller, if you are experienced with the coding of Arduino IDE. You can do potentiometer adjustable feedback on arduino and get a variable voltage, or you can do a fixed feedback and a code for PWM so you have regulated voltages.

    For the USB ports, you can work also with the 5V Standby power rail, which starts as long as you plug the power cord. Is called 5V SB. This is usually 2-2,5A power output, so you can put your USB on that. Benefit is that you don't have to switch the whole power supply to use the USB, and the power supply fans remain off. Otherwise, you can use the red power line. Also you have to put 1A load on the red line to get stability to voltage regulation. You can use LED's to 5V SB to check the correct power input, and also the ATX power supply has a 5V signal for power good / or power ok. Don't forget the signaling to the pins D+ and D- for the USB. It affects the power delivery to the devices and you can do android or Apple compatibility.

    Post again if you want to continue.
     
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