Help with MOSFET circuit design

Discussion in 'Analog & Mixed-Signal Design' started by Joshua64, Jul 9, 2018.

  1. Joshua64

    Thread Starter New Member

    Jul 9, 2018
    3
    0
    Hi all, I know this is probably really basic, but I've done research and have been flooded with information regarding the topic and now can't find what is best for my project.
    In essence, I'm using a motorsport engine management system to trigger a MOSFET using pulse width modulation in order to modulate the speed of some cooling fans.
    Ive got two circuits to make. One with one 7A 12V fan, and another with two 5A 12V fans. Wanting to use low side switching. How do I decide what MOSFET to use and which one is best suited for my use?
    Thanks in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
    19,090
    5,331
    What is the source for the MOSFET PWM signal?
    What is that signal voltage and frequency?
     
  3. Joshua64

    Thread Starter New Member

    Jul 9, 2018
    3
    0
    The source pin of the MOSFET will be grounded, but the gate will be controlled by an auxiliary output on the ems. The signal voltage and frequency is what I can't find in my specs. I may be able to modify this depending on what works best
     
  4. danadak

    Well-Known Member

    Mar 10, 2018
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    You in an automobile environment ? One assumes 12V ...?

    Regards, Dana.
     
  5. crutschow

    Expert

    Mar 14, 2008
    19,090
    5,331
    Can you measure it?
    Do you have an oscilloscope?

    If not, we can assume it's 5V at some reasonably low frequency and go from there.
     
  6. Joshua64

    Thread Starter New Member

    Jul 9, 2018
    3
    0
    It's a management system which has the capability of outputting 5V and 8V
    I believe there are 5v outputs and 8v but I cannot find the frequency
     
  7. crutschow

    Expert

    Mar 14, 2008
    19,090
    5,331
    Is the 5V/8V output the PWM signal?

    Select a logic-level type N-MOSFET [Vgs(th)max ≤2V] with at least a 50V rating and an ON resistance of 10mΩ maximum.
    Connect a 1N4004 diode across each set of fan motor terminals (cathode to plus voltage).
     
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