Finding Thevenin Equivalent Circuit for BJT Problem

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Discussion Overview

The discussion revolves around finding the Thevenin equivalent circuit for a BJT problem, focusing on determining the equivalent resistance and voltage. Participants explore the steps necessary to analyze the circuit, particularly the open circuit condition at the base terminal of the transistor.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant expresses difficulty in identifying the terminal points to consider when making the circuit an open circuit.
  • Another participant suggests that the base terminal connection is the appropriate point to open circuit and confirms the calculation of equivalent resistance.
  • A later reply questions whether the open circuit voltage is equivalent to the voltage at point A, indicating it should be measured with respect to ground.
  • One participant confirms that the voltage at the base terminal would indeed represent the Thevenin voltage for the circuit.

Areas of Agreement / Disagreement

Participants generally agree on the method for finding the Thevenin equivalent, particularly regarding the open circuit at the base terminal, but there is some uncertainty about the specifics of measuring the voltage.

Contextual Notes

Limitations include potential assumptions about the circuit configuration and the definitions of terminal points that may not be explicitly stated in the discussion.

michaelface
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Homework Statement



The question asks to find the Thevenin equivalent circuit as shown in the attachment. (It's a BJT problem, but I'm having difficulty with the first part).

Homework Equations



Where are terminal points I need to worry about when making it an open circuit? That's the biggest question I have.

The Attempt at a Solution



I was able to find the equivalent resistance via R1||R2 + R3, but I don't understand how to find the voltage. Thanks for any help.

michael.
 

Attachments

  • Screen shot 2011-03-28 at 8.09.11 PM.png
    Screen shot 2011-03-28 at 8.09.11 PM.png
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From the figure it seems that the base terminal connection of transistor is the one where you have to make open circuit.
And you have got correctly the Rth by doing so. Now you have to find Vth at the same terminal (i.e, just find voltage at base terminal which is of course open circuited)
 
n.karthick said:
From the figure it seems that the base terminal connection of transistor is the one where you have to make open circuit.
And you have got correctly the Rth by doing so. Now you have to find Vth at the same terminal (i.e, just find voltage at base terminal which is of course open circuited)

So would the open circuit voltage be the same as if I were to calculate the voltage at point A? And I suppose that would mean it has to be the voltage with respect to ground. ie. [PLAIN]http://dl.dropbox.com/u/1981615/Vth.gif

Thanks a lot for your help.
michael.
 
Last edited by a moderator:
Yes, that would be the Thevenin voltage for this circuit.
 
Thanks for you help!
michael.
 

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