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Anyone have a fan control circuit... then a MOSFET ? also

Discussion in 'General Electronics Discussion' started by dangerguy, Oct 2, 2009.

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  1. dangerguy


    Oct 2, 2009
    Hi. I am looking for a fan control circuit that will turn the fan on at 160 degree’s F and off when temperature drops to 130 degree’s F. I built one of my own and managed to get it to turn ON at 130 and OFF at 160. It was turning the fan on as it passed the 130 mark. That didn’t occur to me at 1st. Silly me. Then I tried various circuits I found on the web and even one from a Data Sheet for the LM56 by National Semi.

    I have now built 4 circuits, and not a one of them works as needed. Now I am out here asking if any of you guru’s might have such a circuit or be able to point me to such a circuit, or even dream one up that I can try.

    I have another circuit, a constant current PWM, that is working, but I now understand it is running the MOSFET in “linear mode”. For best functionality, at least as I now understand MOSFET’s, the MOSFET should be running in switched mode. I am not sure this is entirely correct. If this sounds like something you can guide me on, please, educate me. I’ll submit the PWM schematic (just have to get it prepared) if you need it to determine precisely what I mean.

    I’m just an old dog who has been around electronics many years and can usually piece something together when needed. But these 2 circuits are giving me fits. Any suggestions, designs, help of any sort will be greatly appreciated.
  2. Resqueline


    Jul 31, 2009
    Off-on-off as you raise the temperature sounds way more complicated than off-on..
    PWM is by definition switched mode so it'll have to be botched up in the final stage to get it linear..
    I don't have a diagram to contribute with off the top of my head, but if you post (or email) something I'll be happy to correct/simplify it.
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