Project - Control fans from fan header

Discussion in 'The Projects Forum' started by MrWoo, Jan 21, 2009.

  1. MrWoo

    Thread Starter Member

    Jun 18, 2007
    I have been playing with different circuits for some time now, as a hobby. I only know enough to get into trouble, pity that. Anyway, having mobbed the local radio shack and spent some cash at newark, I have a new project, but honestly don't really know what to do.

    All pwm and fanbus stuff aside, I would like to maybe work on something more simple that could be useful as well as a good learning experience.

    If you take a standard 3pin motherboard fan header, no pwm, I have found voltage ranging from 0-12v up to about 4-12v, depending on what the manufacturer decided was a low point. Esepcially with mobo's before pwm.

    How would one properly construct a circuit that would:
    1. Use a dedicated 12v supply from the PSU to drive say 4 fans
    2. Using the 3pin mobo header 12v signal as the signal source

    I would say without proper knowledge that a fet of some kind would be used, ready to take the 12v from PSU and release it to the fan. The 12v signal source would saturate the gate, thus opening linearly the circuit. But, as I understand only the principle, need help to understand if this is proper at all.

    Suffice to say, that, I don't expect anyone to do this for me. But to give examples of properness, and pointers to parts, that I will buy and test with. And most importantly, why using part F123 vs part D123 would be the better choise.

    I have many schematics that show use of op-amps in different ways to do differnet things. I have schematics that show how to use voltage regulators and caps to smooth out pwm's and drive other pwm fans. I have schematics that show how to use things like IRF530's when using pots. Even schematics using small IC's that mainly use pots or or thermistors. I can make these things. But I have not found a simple example of what I am trying now, nor do I specifically want to. I would rather be pointed, and dig in a bit, come back with 'why' and actually learn. If that makes sense.

    So I would like to start with something simple like

    Code ( (Unknown Language)):
    1. 12v psu ---> some fet/transistor ---> load (fan) ---> gnd
    2.                            |
    3.                            |
    4.            12v signal source
    Questions like, would a diode be all that is needed to ensure mobo protection? Is it really this simple? It surely cannot be. There are factors regarding the drivers that I do not understand.

    Thank you.
  2. MrWoo

    Thread Starter Member

    Jun 18, 2007
    So what say you? I don't mind researching and learning here. Does anyone have any initial thoughts on the project I have in mind? Pointers to get started? A good choise for a driver? A simple IC? A reference to a similar project?