About Mosfet Heat sink

Discussion in 'General Electronics Chat' started by sonda, Dec 12, 2012.

  1. sonda

    Thread Starter New Member

    Oct 30, 2012
    10
    0
    Hi,

    i am using a N channel mosfet IRF 1405 to drive a 19A fan motor. the mosfet is controlled by a 10K potentiometer & 50K NTC. my question is what type of a heat sink do i need to use for this Mosfet. thanks In advance.
     
  2. #12

    Expert

    Nov 30, 2010
    16,337
    6,820
    Huge.

    I think you just said you are using the mosfet in the linear region where P=IE and the voltage is unknown. Power = current times voltage. That's why mosfets are usually run as variable pulse width devices. Way complicated compared to just a potentiometer, but much easier to keep cool.
     
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  3. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    A huge one !

    Look up PWM controllers.
     
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  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    You have to calculate the power dissipation, then select a heatsink based on allowable maximum temperature rise.
     
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  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    However, if a FET is used as a "saturated" switch (fully cranked ON), power is calculated as:

    P = (I)squared X (FET ON resistance)
     
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  6. crutschow

    Expert

    Mar 14, 2008
    13,039
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    What is the fan supply voltage? From the maximum power theorem the maximum MOSFET dissipation will occur when the voltage across the MOSFET is 1/2 the supply voltage but that's for a resistive load. Since the fan is a variable load it's more difficult to accurately determine the maximum power point, but it's likely to be no more than 1/2 the supply voltage times 1/2 the maximum fan current.
     
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  7. sonda

    Thread Starter New Member

    Oct 30, 2012
    10
    0
    its supply voltage is 12 volts. thanks a lot!
     
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