How Do You Find the Thevenin Equivalent Circuit for Complex Loads?

In summary, the student is having trouble solving a problem, and is looking for help. He is not able to do it himself, and is looking for someone to help him. He is not allowed to post the answer himself, but is allowed to post a link to a tutorial.
  • #1
snozzla
9
0

Homework Statement


This is in norwegian but hopefully you can understand it.
Here is the assignment and circuit:

http://img835.imageshack.us/img835/3619/krets.jpg
Find the equivalent Thevenin circuit when when RL is the load

Homework Equations


The Attempt at a Solution


I really don't know how to do this, I tried using superposition but that didnt work so good. I know how to do really easy circuits like in my book, but when it gets slighty bit complicated I am very lost.

Would really appreciate some help

Homework Statement


Homework Equations


The Attempt at a Solution

 
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  • #2
Welcome to PhysicsForums!

First step: redraw the circuit so that the load resistor, RL, is on the right. Everything you want to replace with a Thevenin equivalent will be on the left, and this will probably resemble the 'easy' examples you've gotten in the past. Nevertheless, I'll go over the steps below

Second step: figure out what the open-circuit voltage is. Take out RL and find the voltage across the terminals that RL is connected to.

Third step: figure out what the equivalent resistance at the terminals is. Either remove the voltage sources (replace them with short circuits) and then calculate the equivalent resistance, OR figure out the short circuit current: replace RL with a 0-ohm wire, and determine the amount of current that flows through it. The Thevenin resistance will be Voc / Isc.

Good luck!
 
  • #3
Hi, thanks for help!
But I am stuck as ever. I know I have to redraw and remove RL but I am uncapable of doing so. I must be an idiot that doesn't see it. I also have no idea how to exactly calculate voltage across the terminals RL is connected to.

I tried to use superposition and found total resistance and total current from voltage sources 1 & 2. And tried to add this together. So then I got a total voltage and total resistance and I called them Rth and Vth.

I feel I am way off..
 
  • #4
HINT: Notice that when RL is removed, all that is left is a single LOOP.

EDIT: 'Total' voltage and 'total' resistance make no sense in this context, as RL must be removed during the analysis.
 
  • #5
I gave up.. seems I cannot do it.

If anybody is capable and kind, and has enough time to do this I wouldn't mind. It would make me super happy! I want to be able to get this assignment.
 
  • #6
Also, is there any other method of doing this other than Loop Current method, Node Voltage method and Branch Current method?

Can you use something else, like superposition? It doesn't say so I am completely lost as to what exactly I need to calculate things with.
 
  • #7
Why wasnt my post posted? I spent 2 hours on it...
 
  • #8
steffan said:
Why wasnt my post posted? I spent 2 hours on it...

Wow.. I hope you are kidding, if not, I am so sorry ;(:cry:
 
  • #9
Well, I don't know if I got the correct answer, because I'm working with the same problem as you (In 'Høgskolen i Vestfold'). But this helped me alot: http://utwired.engr.utexas.edu/rgd1/lesson09.cfm"
 
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  • #10
Look at this: http://utwired.engr.utexas.edu/rgd1/lesson09.cfm
 
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  • #11
steffan said:
Why wasnt my post posted? I spent 2 hours on it...

It is a difficult situation. Your post basically provided the step-by-step answer, which is generally not allowed here. If you were the original poster (OP) and posted that work, that would be fine. But since the OP is having problems with working out the answer, your providing the answer to him is basically allowing cheating. It's just a difficult situation having you both in the same class and posting here.

On the other hand, having you post the tutorial info link that you did is fine, since the OP still has to do their own work for themselves.

Your post was actually automatically put into Moderation, perhaps for working out so much of the problem, or maybe for some other reason. We were discussing the post just now in the Mentor forums.

I'll PM you a copy of the post, in case you didn't save a copy.
 

1. What is Thevenin's theorem and why is it important?

Thevenin's theorem states that any linear circuit can be replaced by an equivalent circuit with a single voltage source in series with a single resistor. This simplifies complex circuits and allows for easier analysis and calculation of voltage and current values.

2. How do you find the Thevenin equivalent circuit?

To find the Thevenin equivalent circuit, you must first remove the load resistor from the circuit and calculate the open-circuit voltage between the two terminals. Then, calculate the equivalent resistance of the circuit by shorting all voltage sources and open-circuiting all current sources. The Thevenin equivalent circuit will have the same open-circuit voltage and equivalent resistance as the original circuit.

3. Can Thevenin's theorem be applied to non-linear circuits?

No, Thevenin's theorem only applies to linear circuits, where the relationship between voltage and current is constant. Non-linear circuits have varying relationships between voltage and current, making it impossible to find a single equivalent circuit.

4. How accurate is the Thevenin equivalent circuit compared to the original circuit?

The Thevenin equivalent circuit is an approximation of the original circuit, but it is accurate enough for most practical applications. The accuracy depends on the complexity of the original circuit and the precision of the calculations.

5. Can Thevenin's theorem be applied to AC circuits?

Yes, Thevenin's theorem can be applied to AC circuits as long as the circuit is linear and the AC sources are sinusoidal. The open-circuit voltage and equivalent resistance must be calculated using AC analysis techniques, such as phasors or complex numbers.

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