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I'm terrible with power issues

  1. Jul 25, 2007 #1
    Sorry for wordiness, the power problem is probably simple...

    Im a CSE student working on a team trying to create an IBM 704 emulator. It's a big headache, but all that aside, one of our components is a Vortex86 pc104 compatible single board computer (http://www.icop.com.tw/products_detail.asp?ProductID=138)
    with five 48-pin digital I/O modules connected by pc104 ISA bus.
    There will be 180 LEDs that are 3.3V @ 10mA and 60 switches and buttons that will be connected to the I/O modules.

    Anyway they recomend a 5V @ 2.0A power supply for the Vortex board. The Vortex board draws 5V @ 1.1A and each I/O module draws 5V @ 600mA. The power flows through the Vortex board to the I/O modules. We were told there would be a problem with five I/O modules because of the lack of power problem (5 x 600mA + 1.1A). We do have a pc power supply with a 5V @ 2.0A wire we were going to use.

    1. How much current can we send to the Vortex board? We have a 5V @ 20A that would supply enough current, but I'm guessing that would burn the board maybe, I don't know.

    2. If just 2.0A power was connected but the LEDs weren't all on at the same time and I/O boards didn't draw current at the same time, would that work?

    Another option was to power each board separately by not connecting the power pin on the ISA slots, but we would much rather do one of the previous two options. Basically, I'm completely lost with all the power problems... I just don't want to harm the equipment.

    They didn't give us any electrical engineers in this team, but if I use any suggestions from this site I will list it as a resource. I will try to contact the individual responder first.

    UTA Student
  2. jcsd
  3. Jul 25, 2007 #2


    User Avatar

    You can use any current *RATING* of power supply
    that EXCEEDS the sum of the current *RATING* of all
    connected loads.

    You sometimes have to check a power supply's MINIMUM
    rated load necessary for it to function and regulate
    smoothly and properly, but if it's a 5V only PSU
    connected to that many boards, you'll have no problem
    meeting the power supply's MINIMUM needed load.

    So as long as the sum of the specified load currents from
    each board is less than the PSU maximum output current
    rating for its 5V output, you'll be FINE.

    The thing that matters in order not to fry the boards is
    that the PSU VOLTAGE must be of the same polarity
    and guaranteed minimum / maximum limits as what the
    connected devices can deal with.

    5V@2000mA +
    (5V@0600mA * 6) +
    (xV@010ma * 180) =
    2 + 3.6 + 1.8 = 7.4A @ 5V except for the
    LEDS that I guess get powered off 3.3V from the I/O
    modules or something.. anyway...
    the 5V 20A PSU will be just fine for all that and more.

    Just hook up the polarity right and ensure that the PSU
    is well enough (+/- 10% or better) regulated for the
    loads specifications.
  4. Jul 25, 2007 #3


    User Avatar
    Science Advisor
    Homework Helper

    Looks like they sell a 7A power supply for this unit.

    Your best bet is to simply ask the company.
    They should be able to answer your question.
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