Finding Thevenin Voltage w/ Voltage Sources & Zener Diode

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Discussion Overview

The discussion revolves around finding the Thevenin voltage in a circuit that includes a Zener diode and two voltage sources. Participants are attempting to solve a homework problem that involves calculating both the Thevenin voltage (Vth) and Thevenin resistance (Rth), while addressing issues related to their calculations and the implications of circuit components.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents their initial equations for calculating Vth and Rth, expressing difficulty in finding the correct Thevenin voltage due to the presence of a Zener diode and multiple voltage sources.
  • Another participant points out an error in the calculation of Vth2, suggesting that the contribution of one voltage source is being applied incorrectly across the resistances.
  • A participant shares a link to their revised attempt at solving the problem but continues to encounter issues, attributing the problem to potential errors in the homework system.
  • Feedback indicates that while one participant's Vth calculation has improved, they have incorrectly modified their Rth calculation, leading to further confusion.
  • Another participant emphasizes the need to correct both Vth and Rth calculations, indicating that the formulas are correct but the results are not aligning with expectations.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the correct calculations for Vth and Rth, with multiple competing views on how to approach the problem and differing opinions on the accuracy of the calculations presented.

Contextual Notes

There are indications of unresolved mathematical steps and potential misunderstandings regarding the application of circuit theory, particularly in relation to the Zener diode and the configuration of resistances.

sampsoninc916
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Homework Statement



http://l.bitcasa.com/-QwLBhUK

Here is the problem statement

Homework Equations



Vth = V1*R2/(R1+R2)
Rth = R1*R2/(R1+R2)
Vth - Rth*Id - Vz = 0

The Attempt at a Solution



http://l.bitcasa.com/4ycq3BMN

Here is my attempt at a solution.

I am having trouble finding the Thevenin Voltage for a circuit with a Zener Diode with two voltage sources. This attempt at a solution proved to be no help, because as you may have seen in the picture you downloaded, it kept on telling me it was wrong. Once I find the Thevenin voltage, I will be able to find the current through the Zener Diode with the formula Vth - Rth*Id - Vz = 0. May somebody please help me?
 
Last edited by a moderator:
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Your calculation of Vth2 is not correct. You're using superposition to determine the net Thevenin voltage, which is fine, but you have the contribution of V2 being developed across the wrong resistance. Note that for the Thevenin voltage determination R3 will be open circuited (the zener removed) so that no current flows through it.
 
http://l.bitcasa.com/7wz_SYeM I've tried solving for it again, but to no avail. Must be something wrong with the computer system as I may have been on the problem for too long.
 
Last edited by a moderator:
Your Vth looks good now! But you've "broken" Rth. R3 is still in series with the parallel combination of R1 and R2.
 
http://l.bitcasa.com/h1JexqbW

Refreshed the page, solved the equation with different variables using the same methods above, including Vth - Rth*Id - Vz, and it still did not work and it gave me a wrong answer. It's practically mocking me. Something is wrong with the computer system this homework is running on. What am I doing wrong?
 
Last edited by a moderator:
Yeah, now you've broken both Vth and Rth. Why'd you change your Vth calculation?

Redo your math for Rth, too. The formula is right but the result is not.
 

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