Thevenin Equivalent with a dependent source

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

  1. RedDead

    RedDead Thread Starter New Member

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    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

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  2. Jony130

    Jony130 Senior Member

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    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)
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  3. RedDead

    RedDead Thread Starter New Member

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

    Jony130 Senior Member

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    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.
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  5. RedDead

    RedDead Thread Starter New Member

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

    RedDead Thread Starter New Member

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    but where is the 4 ohm resistor which is parallel to the 8 volt source?
  7. Jony130

    Jony130 Senior Member

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    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

    RedDead Thread Starter New Member

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    ah, i get it now
    thanks again
    you saved me ;)
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