# Finding Vth and Zth - Thevenin

Discussion in 'Homework Help' started by brighton53, Jan 30, 2013.

1. ### brighton53 Thread Starter New Member

Jan 16, 2013
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0
Hi I'm trying to find the Thevenin Equivalent Circuit for the following circuit.

So if I've done it correctly the Thevenin Impedance is
(jωL + 1/jωC )/ (jωL * 1/jωC)

but how would I calculate Vth - as I'm not sure what to do regarding source transformations?

Thanks !!

2. ### Georacer Moderator

Nov 25, 2009
5,150
1,271
Take a look here and here. Come back with your questions.

3. ### brighton53 Thread Starter New Member

Jan 16, 2013
7
0
Thanks for linking me to that. I understand the theory behind it it's just that I don't know what to do because of the current source being their, once they're all voltage sources I can do it fine.

So whats the best approach to make them all voltage sources. because I can't see a way of changing the current source to a voltage source as there's no parallel impedance. and if I was to convert the voltage source to a current source - I'm not sure what I would use as the parallel impedance.

Cheers Sam

4. ### Georacer Moderator

Nov 25, 2009
5,150
1,271
You don't need to turn the current source into a voltage one. Just apply the Thevenin theorem:

1. Remove the load calculate the Thevenin voltage across its terminals. You will need to use the superposition theorem for that (also included in the AAC e-book), since you have two sources in the circuit.
Consider all of the variables as known quantities.

2. Nullify the two sources and calculate the Thevenin impedance as "seen" from the load terminals.

3. Replace all of the external circuit with a voltage source with value equal to the Thevenin voltage in series with the Thevenin resistance.

4. Connect your load in series with the Thevenin resistance.

5. ???

6. Profit!

Is that clear?

brighton53 likes this.
5. ### brighton53 Thread Starter New Member

Jan 16, 2013
7
0
Yes thanks !! - I guess from doing examples where I've always done source transformations I thought it was to go.

Cheers !!