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#1
12-12-2010, 10:21 AM
 RedDead Junior Member Join Date: Dec 2010 Posts: 14
Thevenin Equivalent with a dependent source

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
Attached Images
 IMAG0012.jpg (285.0 KB, 62 views)
#2
12-12-2010, 10:51 AM
 Jony130 Senior Member Join Date: Feb 2009 Location: Poland/Wroclaw Posts: 2,509

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)
 The Following User Says Thank You to Jony130 For This Useful Post: screen1988 (05-01-2013)
#3
12-12-2010, 11:11 AM
 RedDead Junior Member Join Date: Dec 2010 Posts: 14

Quote:
 Originally Posted by Jony130 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)
i know that, but i am confused about how to start because there is a dependent source.
how can i find Vx?
#4
12-12-2010, 01:10 PM
 Jony130 Senior Member Join Date: Feb 2009 Location: Poland/Wroclaw Posts: 2,509

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.
 The Following User Says Thank You to Jony130 For This Useful Post: screen1988 (05-01-2013)
#5
12-12-2010, 01:31 PM
 RedDead Junior Member Join Date: Dec 2010 Posts: 14

thank you, you are brilliant

Last edited by RedDead; 12-12-2010 at 01:38 PM.
#6
12-12-2010, 01:43 PM
 RedDead Junior Member Join Date: Dec 2010 Posts: 14

Quote:
 Originally Posted by Jony130 Well first you need to find Vth voltages
but where is the 4 ohm resistor which is parallel to the 8 volt source?
#7
12-12-2010, 01:50 PM
 Jony130 Senior Member Join Date: Feb 2009 Location: Poland/Wroclaw Posts: 2,509

Well I remove this resistor becaues it is connect parallel to the voltage source.
So this resistor has no effect on Va voltages.
#8
12-12-2010, 02:17 PM
 RedDead Junior Member Join Date: Dec 2010 Posts: 14

Quote:
 Originally Posted by Jony130 Well I remove this resistor becaues it is connect parallel to the voltage source. So this resistor has no effect on Va voltages.
ah, i get it now
thanks again
you saved me

 Tags dependent, equivalent, source, thévenin

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