IRFZ44N mosfet connections

Discussion in 'The Projects Forum' started by jayanthyk192, Jul 28, 2010.

  1. jayanthyk192

    Thread Starter Member

    Jan 23, 2010
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    hi,

    i'm makind stepper drive circuit using an IRFZ44N mosfet.the connections i made are shown.i gave 12V from an SMPS having a max current of 23A.even though the gate was zero,i measured a current of 2.2A in the drain-source.the mosfet was very hot(really hot).(i connected the multimeter in between V+ and pin of the mosfet).please correct the circuit if there are any problems.i want V+ as 12V.

    the rating Vdss is 55V.i assumed it is the max voltage across D&S.please verify.

    thank you
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    You show a box, not a Mosfet. A Mosfet has its drain and source pins marked.
    Maybe you have its drain and source pins connected backwards so its body diode is conducting.

    Its max allowed drain to source voltage is 55V but it will work fine with less voltage.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,677
    900
    Please post a real schematic. What you show will have a dead short when the mosfet turns on. No wonder it gets hot!

    It is important to show where the load is in the circuit. Is the mosfet sinking current from the load (that is, the source of the mosfet is connected to ground) or is the mosfet supplying current (i.e., its source is connected to the load). In either case, show how you are driving the gate.

    John
     
  4. jayanthyk192

    Thread Starter Member

    Jan 23, 2010
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    ok,here's a proper schematic.this is the first time i'm using mosfet.what i did was connect 12V to a multimeter(measuring current)and the other lead to the drain.that might be the mistake.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The IRF44Z Mosfet completely turns on when its gate is 10V, not 5V. With only 5V then some of the IRF44Z Mosfets are only partially turned on where they get very hot.
    Use a "logic-level" Mosfet that completely turns on with a gate voltage of only 5V.

    Before the Mosfet was conducting 2.2A when its gate was 0V then it should not conduct anything. Why?
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    I do not think 5 volt as VGS is enough to turn your FET compleatly on. For that you need at least 10 Volt from a quick look on the data sheet. But it may be other error also. Check the pin configuration
     
  7. jayanthyk192

    Thread Starter Member

    Jan 23, 2010
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    i saw in the datasheet that at Vds=55V,gate=0V the leakage is 25microamps.so i thought it isn't proper.

    after connecting the coil of the hard disk,a current of 1.8A is flowing without gate connected to anything,but as i conneted the gate to ground(0V)the current became 0.14A which is quite good but not not good enough.how do i get it to 0.1 or less?
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The gate must be connected to something.
    Since your Mosfet does not turn off when it should then it is destroyed. Maybe it got fried.
     
  9. jayanthyk192

    Thread Starter Member

    Jan 23, 2010
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    i don't think so because they are completeky new ones and the ecess is only .14 amps,which still is undesirable.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Your first post said that the Mosfet was very hot. So it got fried.

    The max leakage current is only 25uA when it has a very high D-S voltage of 55V and will be much less when the D-S voltage is only 12V.
    If your meter is accurate, you know how to read it and it is connected properly then your measurement of 140mA is about 14,000 times too high.
     
  11. TrevorP

    Active Member

    Dec 8, 2006
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    Stick a pulldown resistor on the gate as well (around 10k), this will prevent the FET from turning on due to miller effect when the input might be floating.
     
  12. khmtambi

    New Member

    Apr 7, 2010
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    may be some of your pins are short. it happened with me. i usd STP55NF06L same like IRFZ44N. by mistake i shorted gate and source or drain. so it got very hot.try using 22k ohm resistor between gate and source.
     
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