# Thevenin's Equivalent Circuit

Discussion in 'Homework Help' started by wheeltiger, Nov 17, 2007.

1. ### wheeltiger Thread Starter New Member

Mar 19, 2007
6
0
How can I find the Thevenin's equivalent of this circuit?

I have replaced the voltage source with short circuit...
$Z_{TH}=(5\Omega+j\Omega)$ PARALLEL $j3\Omega$

but I don't know what I need to do with the $4\Omega$

and I don't know how to find $V_{TH}$ too...

Please help!

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2. ### sohcahtoa Member

Nov 7, 2006
15
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I'm not sure what they're getting at with the 4j either. I'd say ignore it.

I have to run to class, so I'll try to answer as quick as possible.

I did the following to figure out the Thevenin equivalent:

1) Remove the load (Zl)

2) Make the input voltage a short.

3) Now you are looking for Rth seen from the right side of the circuit. In redrawing the circuit, you can see that 5ohms and j(ohms) are in parallel. So far we have (5 || j). Considering this to be one impedance (say, Zparallel), and redrawing the circuit, you can see that Rth is actually Zparallel in series with the 3(j) inductor.

Therefore, Rth = 3j + (5 || j)

4) Now Vth is the voltage seen at the load terminal with the load removed. So we have a voltage divider between the 5ohm resistor and 1(j) inductor, as the voltage seen at the far end of the 3(j) inductor is the same as the node between 5 and (1)j since there's no load Zl.

The voltage at the voltage divider node is then V(1j/(5+1j))

So your Thevenin equivalent is V(1j/(5+1j)) in series with 3j + (5 || 1j) in series with the original load impedance, Zl.

Does that sound right?

3. ### abbas_6007 New Member

Sep 7, 2009
5
0
Hello.
I will answer to your problem 2moro. i am a new user of this site.

4. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,621
468
You can't ignore it. The two inductors are coupled and the 4Ω is a measure of the mutual inductance between the two. You must take it into account to get the Thevenin equivalent.

5. ### Perfectboy New Member

Sep 9, 2009
9
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Right! You can't ignore it as said. I have got the right answer.