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Thread: Sproggy's PSU is HOT! (and customization question)

  1. #1
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    Red face Sproggy's PSU is HOT! (and customization question)

    Okay, I just finished my Sproggy Mk2.6 with an ATX connector. It can boot my system, but in a short ammount of time, the Max787 (5v regulator) starts to get VERY hot. I have a large heatsink on it, and I'm still afraid that it'll blow if I leave it on for too long (especially during the middle of a hot day.).

    I can only assume that I'm trying to draw too much from it, and I haven't even hooked up my LCD to it yet

    I noticed that LittleJ added another Max787 too give him more amps on the 5v line, but I'm wondering if this will actually help keep my device cool. Wouldn't it split the load and make it run cooler?
    I can't really make heads or tails of the images on his site because of the poor quality, but he just jumped the pins of the new regulator to the equiv. of the other right?

    Thanks in advance,
    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

  2. #2
    Retired Admin Aaron Cake's Avatar
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    Cool

    In theory, adding another regulator will split the load. In practice, it may not work that way. You may need to go and buy two more regulators in a matched set to make sure each one outputs the same voltage. If one outputs a higher voltage than the other, it will sink more current and heat up. Also, a small fan will do wonders.
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  3. #3
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    Good to see that someone visited my little site and found it somewhat useful. The one thing that I did notice is that the heat on the MAX787 did DRAMATICALLY reduce when I added the second regulator. But I still had a fan by the heatsink too.

    I agree with Aaron that finding a matched set of voltage regulators would be nice, but even without matched set the current load should split across both regulators (but somewhat unevenly). But even an uneven split it should help a bit with the heat...
    j
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  4. #4
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    Thanks for the confirmation... What do you mean "Matched set of regulators". I got both of them from Maxim (same part number, same shipment), shouldn't they be the same?

    And am I right in connecting the same pins together (pin1 to pin1, pin2 to pin2, etc.)?

    Thanks
    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

  5. #5
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    I don't want to step on Aaron's toes here (and hopefully I have this right): even though two voltage regulators may have the same part number (ie MAX787) they output voltages that they are regulated to may be a few milli(or micro)-volts different. The regulator with the higher voltage will supply more current thus heat up more. A "matched set" of voltage regulators have the exact (or as close a possible) output voltages, so heat dissipation would be more even... (That was the quick 30-second explanation)

    And yes you're right. Just run the regulators in parallel (pin 1 - pin 1, pin 2 - pin 2, etc...)

    Hope this helps.
    j
    j's MP3Car.com Web Site
    [######----] 60% complete (1st try)

  6. #6
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    And how do you specify and order a matched set of regulators? I don't think Maxim offers this service.

    A classic way to force current sharing is to put a small value power resistor in series with the output of each regulator.

  7. #7
    FLAC Mastero's Avatar
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    man just put a good heat sink and put a small 2" 12vdc fan to cool it thats it the 788 will work fine with no problem.

    Mastero

  8. #8
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    Well, I finally got the second reg. on there with much fuss (solder doesn't stick to the board when you've removed all the copper ).

    It doesn't run any cooler, but at least I've got the extra amps (I hope).

    If I put a fan on it, it's just warm to the touch, so I'm not worried. I was just surpised my how hot it can get sitting in sill air.
    a small fan will do wonders.
    Damn Right!

    Thanks guys!
    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

  9. #9
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    You sure your coil and rectifier would handle the surge?Don't forget that MBR745 is rated for 7A... the best thing would be adding another MAX787 with all componenets,i.e. double the 5v section.
    Enjoint life!

  10. #10
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    Okay, it does work with my present arrangment... But I don't wanna blow something out down the road.

    How about if I used an MBR1645

    I can't seem to find a coil that would meet the current requirments.

    I'm beginning to wonder if the second regulator is actually doing anything. It's just as hot as before. Without all the other components, it seems like it wouldn't work at its full potential anyway. I don't want to add all that other stuff, because I'd have to redesign the whole board.

    How can I test it so I know what kind of amps I'm getting?

    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

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