Simple Thévenin equivalent?
June 14, 2010 7:36 PM Subscribe
What is the Thévenin equivalent of this circuit?
I have this circuit. I am required to find the Thévenin equivalent voltage and impedence of this circuit as seen by the capacitor C. An algebraic expression is required.
I arrived at the solutions Vth = (R3*Vi)/(R2 + R3 + R4) and Rth = R3(R2 + R4)/(R2 + R3 + R4), but my friend has 1/(1/R1 + 1/(R1 + R4)) as the solution.
Are either of us right? Many thanks for any light Mefites can shed on the matter!
I have this circuit. I am required to find the Thévenin equivalent voltage and impedence of this circuit as seen by the capacitor C. An algebraic expression is required.
I arrived at the solutions Vth = (R3*Vi)/(R2 + R3 + R4) and Rth = R3(R2 + R4)/(R2 + R3 + R4), but my friend has 1/(1/R1 + 1/(R1 + R4)) as the solution.
Are either of us right? Many thanks for any light Mefites can shed on the matter!
Best answer: (And I can confirm to the best of my abilities that you are completely right; you can check your answer by computing ITh and checking that VTh = RThITh (see).
posted by Monday, stony Monday at 8:31 PM on June 14, 2010
posted by Monday, stony Monday at 8:31 PM on June 14, 2010
Best answer: I agree with Monday, stony Monday-- your R_th appears to be correct. Noting KCL around the outside loop, your expression for the current through R3 and subsequent expression for the open-circuit voltage at the output nodes appears correct as well.
posted by thack3r at 10:57 PM on June 14, 2010
posted by thack3r at 10:57 PM on June 14, 2010
Response by poster: Thanks a lot, guys/girls. Upon closer inspection (warranted by your responses!), we agreed that my answer appears to be correct.
The uncertainty arose from my friend's insistence that the professor had given the other solution, but it turns out that they had made a mistake in copying it down. :-)
posted by PuGZ at 11:06 PM on June 14, 2010
The uncertainty arose from my friend's insistence that the professor had given the other solution, but it turns out that they had made a mistake in copying it down. :-)
posted by PuGZ at 11:06 PM on June 14, 2010
I am not a big fan of homework filter as it often is a way of avoiding doing the work yourself. After someone has completed the work, and especially when it is relatively complex like a Thevenin analysis, then having it checked here seems appropriate. I recently had some trouble trying to help my son with his physics analyzing a circuit. I felt better after asking an electrical engineer to help us and even he had trouble. Thevenin provided an answer, but he had not been taught that so we had to brute force a loop analysis. Both my son, the EE and I were doing it right from the beginning, but the math was voluminous enough that we all made some errors along the way. Having an answer from AskMe would have been helpful to check for those errors and I think that would be an appropriate use of AskMe. I used SPICE instead. Anyway I am glad PuGZ got his answer here.
posted by caddis at 12:57 PM on June 15, 2010
posted by caddis at 12:57 PM on June 15, 2010
This thread is closed to new comments.
posted by Monday, stony Monday at 8:21 PM on June 14, 2010