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Voltage repeater or cloner ??

Discussion in 'General Electronics Discussion' started by Nancy, Jan 21, 2009.

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  1. Nancy


    Jan 21, 2009
    Hi. I am not at all sure what to call what I am looking for. I have a very little knowledge of dc circuitry. I understand basics, have played with and learned a lot from little circuits involving transistors/fets and small things like 555's.

    I am wishing to learn more, so I picked what I thought would be an easy project. I have an old motherboards here, so I can play. So I have 2 tests.

    1. Use a motherboard 3pin fan header, which normally drives 1 12v fan, to drive 4 fans. I will assume that the overall power consumption for each fan will be .25a, and that the fan header will be max of 1a. So this will require a seperate 12v source that will be turned on/off with something like a fet or transistor. So the project is to use the incoming 12v (assuming it is ranging from 0-12v, but depending on motherboard, I have seen 6-12v and 4-12v) signal to drive the fet(s), which in turn drive the 4 fans.

    2. Same situation, except I have a motherboard where the 3pin fan header appears to be pwm. I don't understand how to do the project with this type of signal though I understand what pwm is.

    So, do I look for some kind of voltage repeater? Where I have the 12v signal, and use that to saturate the fet(s), which in turn open the other 12v to the fan? I do not mind frying the motherboards, but in respect to being able to continue testing, don't wish to.

    I have looked at many different opamp circuits, and many transistors/fets, but honestly, I don't completely understand much about them except the loads and voltage saturations.

    Is there anyone who could help give tips on designing this small circuit, and what the downfalls or cautions should be on such things? Also, in interest of always trying something new, and protecting the motherbaord fan header, is it worth the time to learn something about optocouplers or such to keep actual seperation of circuit from motherboard.

    I hope this is making sense, as there is so much terminology for a home tinkerer that it makes my head swim.

    Thank you for any help.
  2. neon


    Oct 21, 2006
    first is the 12 power able to drive all these fans. If so then why mess with it just run them in parallel. ANYTHING YOU ADD will make things worst if the power is not there to begin with.
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