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Thread: How is this for a Supply....

  1. #11
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    There are some regulators that require 12.5volts minimum input, this is what I am using, add a transistor and the input would have to be 13.5 - 14.5 volts, which is still too high,
    eg. you have your headlights on, and blast your horn, the voltage drops .5volt, the regulator cant regulate properly and your computer crashes.....

  2. #12
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    Speaking of Heatsinks and fans.....
    How would this do????

    And mount it like this....

    That is what I have done.....

  3. #13
    FLAC
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    you sure do ask alot of questions before waiting for answers.

    the transistor on the 5V rail using the above circuit WILL get hot.... and very hot at that.... even with a P75/P90... if you try that with say a P233+ you will be frying eggs on the transistor/heatsink not powering computers with em!!!

    your best bet is to look at building a switchmode supply like sproggy's.... www.sproggy.com.... check out the power supply section a few guys there are getting pretty serious about building PSU's...
    Project - GAME OVER :(

  4. #14
    Retired Admin Aaron Cake's Avatar
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    Red face

    Originally posted by THE_SKINNY_MP3_KID:
    <STRONG>It won't generate too much heat with 5volts, if you use a 10amp transistor, then only draw 4-5amps the heatsink will get warm, but not hot....
    </STRONG>
    It will generate a tonne of heat at 5V. Someone else did the calcs and it was over 100W. That's not a lot of heat? Put your hand on a 100W lightbulb and tell me that's not a lot of heat. Using a 10A transistor will make no difference at all. It will get just as hot.

    Oh, and that heatsink you pictured looks to be for a PII or PIII. Remember that the power dissipation of these chips is only around 40W (if I remember correctly). So your looking at a heatsink three times as big, or one the same size with three times the airflow.

    I would highly suggest looking at building a switching supply instead of a linear one.
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  5. #15
    Dustin Haug
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    Actually, I will change what I said, the regulator on its own needs atleast 14.5volts to regulate properly, add a transistor and it would be more like 16volts....
    IT WON"T WORK!!!!!!!!!!!!!!!!!!
    Look at the schematic, the transistor and regulator aren't in series, so you don't need to add the voltages like that. With the transistor like that I'm guessing that Vce would be around 1-1.5V (I'd look it up but I'm lazy ) which with a 14.5V input leaves you 12V at the output. Now unless the 3.3 ohm resistor causes a rather large voltage drop the IC will still have plenty of voltage above 12V to work with because the 3.3 ohm resistor would have to cause around a 1.5V drop to cause the regulator to drop out. I'm not saying that this circuit is a good solution, just that in theory it would work. A switching supply is like what Jeff Mucha made is a far supperior solution.

  6. #16
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    No.....
    I looked it up....
    The regulator on its own NEEDS 14.5 volts...
    and addind a transistor increases that because you are drawing a higher current....
    look, I know what I am talking about....
    My dad is an electronics engineer....
    Everything I know, and post is what he agrees with....
    You can't argue with someone who has had 5 years of training, can you....
    The five volts WOULD work it is only 25-35watts MAX, not 100, where did you get that number from....
    Anyway, it will work...
    It's cheap....
    It's easy....

  7. #17
    Dustin Haug
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    I didn't look up the exact requirements of that IC but most of them don't need 2.5 volts of headroom. Most linear regulators I've used in the past need approximately 1-1.5 Volts. Anyways, I am an eletrical engineering student myself (senior year), and although I haven't built this because it isn't very practical I still think it would work. But again there isn't any point to arguing about it because there are much better solutions available anyways.

  8. #18
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    Do you know how much sproggys power supply would cost to make??
    Like, I have $0 in my wallet, and about $18 in the bank...
    now tell me, HOW CAN I AFFORD IT!!!!!!!!!

  9. #19
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    Originally posted by THE_SKINNY_MP3_KID:
    <STRONG>Do you know how much sproggys power supply would cost to make??
    Like, I have $0 in my wallet, and about $18 in the bank...
    now tell me, HOW CAN I AFFORD IT!!!!!!!!!
    </STRONG>
    you save up that pocket money you get every week and in time you will have the cash to buy the parts.... sheesh!
    Project - GAME OVER :(

  10. #20
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    I can't save my money, I get $4 a week and spend it before I get it....
    anyway, I already have all the parts I need for my power supply, and IT WILL WORK FOR 5 VOLTS!!!!!!!!


    not for 12...

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