Vgs on Shockley Curve/ Vgs calculation?

Discussion in 'Homework Help' started by no12thward, Feb 13, 2011.

  1. no12thward

    Thread Starter Member

    Jan 10, 2011
    30
    0
    For this transistor circuit, I have drawn in my points and estimated Vgs on the Shockley Curve; But when calculating Vgs mathematically (Vgs= Vg-Vs) to check, I get 0V-5.5V= -5.5V (Vg always=0V). That is terribly off from my -1.54V Vgs value estimated at the bottom of my Shockley curve. I though the Vgs values from curve and calculation are supposed to be slightly the same? Any help?

    Thanks guys!
     
  2. no12thward

    Thread Starter Member

    Jan 10, 2011
    30
    0
    also, if Vds= Vd-Vs, and is to always be positive, why am i getting 3.5v-5.5v= -2?
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I have Id=2.74mA and Vgs=-2.48V
     
  4. no12thward

    Thread Starter Member

    Jan 10, 2011
    30
    0
    i guess im just not seeing how you derive that
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I_D=I_{DSS}(1-\frac{V_{GS}}{V_P})^2

    Must satisfy

    V_{GS}=3-2000I_D

    Where ID is in ampere.

    I substituted the second relationship into the first and solved for ID, given IDSS and VP.
     
    no12thward likes this.
Loading...