Drain current differs from source current? NMOS

Discussion in 'General Electronics Chat' started by KaloyanP, Oct 11, 2012.

  1. KaloyanP

    Thread Starter New Member

    May 27, 2012
    5
    0
    Hi, I have been researching transistors for a PWM drive for a small motor and the one I have chosen for now is the RSQ 035 NO3 (it will form the lower half of a discrete H-bridge). However, I noticed that the maximum current for the drain is about 3.5 times bigger than the one for the source. How does that work? Where would the current go if it doesn't go through from the drain to the source?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    All the drain current has to go through the source.

    Could you post a reference to the data sheet for that MOSFET? I couldn't find it.
     
  3. KaloyanP

    Thread Starter New Member

    May 27, 2012
    5
    0
    Exactly, that's what I know as well, but they keep insisting on the two currents being different throughout the datasheet :)

    I goofed up with the spacing in the name, heres a reference to the datasheet :)

    http://datasheet.elcodis.com/pdf/5/78/57838/rsq035p03tr.pdf

    P.S. I probably should think twice before posting so late in the night... Just noticed that the second rating is for the body diode, which now makes a lot more sense :) The moral of the story is: kids, read your datasheets twice, they don't lie unless they are totally wrong.
     
  4. cabraham

    Member

    Oct 29, 2011
    82
    30
    Is = Id +Ig. Is = source current, Id = drain current, Ig = gate current.

    With high frequency PWM rectangular drive waveforms, the gate current is not negligible. So Id & Is will not exactly match because their difference is the gate current Ig, which is non-zero. Make sense?

    Claude
     
    Last edited: Oct 17, 2012
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