PWM Computer Fan Control via 3 Pin header

Discussion in 'The Projects Forum' started by fcollingwood, Dec 9, 2014.

  1. fcollingwood

    Thread Starter New Member

    Dec 9, 2014
    2
    0
    Hi All

    I'm looking into a circuit for controlling a 4 pin PWM fan from a 3 pin motherboard header.

    Typically the 3 pin motherboard header (ignoring the sense pin) will vary the voltage supplied to a 3 pin fan from 7V to 12V DC.

    The PWM fans on the other hand (Again, ignoring the sense pin) have a constant 12V supply, with a 5V PWM signal applied to the 4th pin at a frequency of 25kHz. 0-100% duty cycle will vary the fan speed from 30-100%.

    So what I'm looking for is a circuit that will give a 5V 25kHz PWM output with an analog input varying the duty cycle from 0% at 7V input to 100% at 12V input

    Has anyone done this before? Or does anyone have any suggestions?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
    1,105
    Doable. I'll post a circuit in due course.

    Edit:-
    Welcome to the forum!
    Here you go
    PWM(custom).gif
     
    Last edited: Dec 9, 2014
    fcollingwood likes this.
  3. fcollingwood

    Thread Starter New Member

    Dec 9, 2014
    2
    0
    Good one, thank you!
     
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