IRFI9520G current sharing

Discussion in 'General Electronics Chat' started by GibbyG, Sep 6, 2014.

  1. GibbyG

    Thread Starter New Member

    Sep 3, 2014
    9
    1
    IM trying to share current across 2 mosfets.
    The load is 5.5a and the 2 mosfets are rated for 5A each.
    When I turn them on the temp on both mosfets flies on up to 80°C and I shut them down before they burn the house down.
    Am I setting these up incorrectly?

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  2. #12

    Expert

    Nov 30, 2010
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    Do you have them attached to heat sinks?
     
  3. GibbyG

    Thread Starter New Member

    Sep 3, 2014
    9
    1
    I was hoping that by sharing them down to 50% rating I could get away without needing one.
     
  4. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    No. Look at the datasheet. If RdsON = .6 ohm and I = 2.75, P = 1.65W. With theta Ja = 65, that's 107.25 centigrade rise in temperature.

    There are much better mosfets available.
     
  5. GibbyG

    Thread Starter New Member

    Sep 3, 2014
    9
    1
    Okay I tested again after mounting them both on a north bridge heatsink and it kept the temp down to 50°C.
    I also noticed that when I connect the load directly to 12v the amps read 6.3A rather than 5.5A
    Seems there is some loss through the mosfets.
    A better option seems to be to just use a good ol' relay for these.
    Comes out to the same package size after you factor in the heatsink.
    The mosfet idea was just to save space and switching speed is not a factor.
     
  6. #12

    Expert

    Nov 30, 2010
    16,284
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