1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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;
    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):

    |                   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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook