# Thevenin Equivalent with a dependent source

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

Dec 12, 2010
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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

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2. ### Jony130 AAC Fanatic!

Feb 17, 2009
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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)

screen1988 likes this.

Dec 12, 2010
14
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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 AAC Fanatic!

Feb 17, 2009
4,174
1,188
Well first you need to find Vth voltages
So diagram look like this

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

And now we need to find Isc

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.

Dec 12, 2010
14
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thank you, you are brilliant

Last edited: Dec 12, 2010

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

7. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,174
1,188
Well I remove this resistor becaues it is connect parallel to the voltage source.
So this resistor has no effect on Va voltages.