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MOSFET Without Rs (source resistance) Help

  1. Jan 10, 2012 #1
    I'm encounter a problem in biasing mosfet irf510 ;
    please someone answer me... why i can not get an output over than 3V

    i had using voltage divider to bias at 4.5V (R1=R2=100K) ; Vdd=9V; Vout should be = 3V .. Rd=600 OHM where Id=10mA the problem here that i do not like to use Rs as source resistor . the worset of result is not as i calc ...pleeez some one tell me why can not get an out put equal to 3V .. why Id not as i determinted ?

    best regard;
    MR,10GHz
    it should be mentained here that when you put Rs ; you will get what you want; and my colpitts oscillator then work in Common Source; when you remove Rs and recalc the circuit its faild

    Kn=124 mA/V2 @ gfs =1.3@3.4A
    iD=kn (Vgs-Vgs(th))^2
     
    Last edited by a moderator: Jan 10, 2012
  2. jcsd
  3. Jan 10, 2012 #2
    I'm not sure I understand your question. I think you're saying you have a Vdd or 9V, an Rd of 600 ohms and an Id of 10 mA. The 600 ohms with 10 mA with give you a voltage drop of 6V and 9V - 6V = 3V.

    If you want more than 3V at the drain you could either lower your bias voltage or the value of Rd.
     
  4. Jan 10, 2012 #3
    yes that's right but in practical in my lab when i build the circuit it's did not success why?

    Code (Text):

    9V
    |-------------|
    |                   Rd=660
    R1=100K        |-----------------V0 = should be >5 put in practical about 300mv Why?
    |                --
    |-----------| IRF510
    |                --
    R2=100k         |
    |                   |
    |                   |
    ---------------
           ---
             -
    --
    -
     
     
    Last edited by a moderator: Jan 10, 2012
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