Thevenin Equivalent with a dependent source

Discussion in 'Homework Help' started by RedDead, Dec 12, 2010.

  1. RedDead

    Thread Starter New Member

    Dec 12, 2010
    14
    0
    Find the Thevenin Equivalent circuit between A and B
    the circuit is in the attachments...
    i don't know how to start
    and what is the difference if A and B were for e.g after the 6V source?

    thanks :D
     
  2. Jony130

    Senior Member

    Feb 17, 2009
    3,859
    1,067
    To find Thevenin's equivalent at terminals a & b you need to find

    1. The open circuit voltage Vab = Vth.
    2. The current flowing from a to b when a & b are shorted together.
    3. Hence find Rth = Vab(open circuit)/Iab(short circuit)
     
    screen1988 likes this.
  3. RedDead

    Thread Starter New Member

    Dec 12, 2010
    14
    0
    i know that, but i am confused about how to start because there is a dependent source.
    how can i find Vx?
     
  4. Jony130

    Senior Member

    Feb 17, 2009
    3,859
    1,067
    Well first you need to find Vth voltages
    So diagram look like this

    [​IMG]

    Vth = - V1 * R2/ (R2+R3) = -3.2V

    And now we need to find Isc

    [​IMG]

    So I write nodal equation

    (Va - (-8V) )/3Ω = (0V-Va)/1Ω + ( (-5•Va) - Va )/2Ω

    So the only think you need to do, is to find voltage at Va node.
     
    screen1988 likes this.
  5. RedDead

    Thread Starter New Member

    Dec 12, 2010
    14
    0
    thank you, you are brilliant :D
     
    Last edited: Dec 12, 2010
  6. RedDead

    Thread Starter New Member

    Dec 12, 2010
    14
    0
    but where is the 4 ohm resistor which is parallel to the 8 volt source?
     
  7. Jony130

    Senior Member

    Feb 17, 2009
    3,859
    1,067
    Well I remove this resistor becaues it is connect parallel to the voltage source.
    So this resistor has no effect on Va voltages.
     
  8. RedDead

    Thread Starter New Member

    Dec 12, 2010
    14
    0
    ah, i get it now
    thanks again
    you saved me ;)
     
Loading...