Mosfet RDSon Testing Method

Discussion in 'General Electronics Chat' started by yasinji, Jun 5, 2009.

  1. yasinji

    Thread Starter Member

    Mar 25, 2009
    12
    0
    Kindly provide a Mosfet RDSon esting method.
    I have tryed by using two power supply each limited to 1A and kept 10V as Vds and 9V as Vgs. The Mosfet has turned on and the taken the drop across the Vds and got less than 17mE. But may due to gate charge or some other reason the mosfet is failing. I was using this mosfet testing in our QA dept for production. How to avoid mosfet failure?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A schematic would be helpful.
     
  3. radiohead

    Active Member

    May 28, 2009
    474
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    Do you have the data sheet for the MOSFET in addition to what Mik3 asked for?
     
  4. yasinji

    Thread Starter Member

    Mar 25, 2009
    12
    0
    Dear Mr. MIk3,

    I have attached the ckt. Kindly verify and please suggest a solution to my problem. I have also attached the daasheet of mosfet device under test.
     
  5. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    that fet has Rds-on of typ 17mOhm @ 10Vgs. thats exactly what you measured (1A X 0.017mOhm = 0.017V).

    are you asking why you measured 17mV with 9Vgs?
     
    Last edited: Jun 6, 2009
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Are you sure the source is limited to 1 Amp?

    Also, with the 120K and 150K resistors the voltage on the gate will be about 6V which is not enough to turn the MOS fully on. Replace the 120K with a 100 Ohm one.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Your MOSFET may be failing because it has to discharge the power supply's internal capacitor before the voltage drops to 17mV (or whatever). This can cause a lot of power to be dissipated for a short amount of time.
    I would limit the current with a 10 ohm, 25 Watt resistor in series between the supply and the drain. That way, you avoid the current spike.
     
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