Calculating Emitter Current - Voltage-Divider Bias

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Discussion Overview

The discussion centers on the calculation of emitter current (IE) in a Voltage-Divider circuit using two different methods: the Voltage Divider Method and the Thevenin Equivalent Method. Participants explore the consistency of results obtained from these methods and the conditions under which each method is applicable.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that both the Voltage Divider Method and the Thevenin Equivalent Method can be used to calculate IE, but they express uncertainty about whether the methods yield consistent results.
  • One participant notes a specific difference of 0.31mA between the two methods and questions if this difference is acceptable.
  • Another participant highlights a concern about a 6% difference in calculations, suggesting it may be too large for rounding errors.
  • Some participants mention that the Thevenin method is typically used for loading effects, while the Voltage Divider Method is for unloaded effects, raising questions about the applicability of each method in different scenarios.
  • A participant indicates that they have encountered problems where it is unclear whether the circuit is loaded, complicating the choice of method.
  • One participant asserts that the same answer should be achievable unless there are mistakes in calculations or assumptions made during the process.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the two methods can be used interchangeably, as there are varying opinions on the acceptability of the differences in results and the conditions under which each method should be applied.

Contextual Notes

Participants express uncertainty regarding the assumptions about loading effects in the circuit and the potential for calculation errors, which may influence the results obtained from each method.

?n0t_A_nUmb3R?
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I am aware that there are two methods of working out IE for a Voltage-Divider circuit.

The first is:
https://www.google.co.za/search?q=V...redoc.org%2Fdocs%2Findex-114597.html;2048;730
And then work out VE = VB - VBE

And the second is:
https://www.google.co.za/search?q=v...rcuits.com%2Fvol_3%2Fchpt_4%2F10.html;480;257
(VTH and RTH)

I then tried to calculate a specific problem using both methods. The results were not consistent and varied.
My question is can we use both methods (first and second above) interchangeably?
Are there any differences between the two methods?
 
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?n0t_A_nUmb3R? said:
I then tried to calculate a specific problem using both methods. The results were not consistent and varied.
Then please show what you did and which setup you mean. Otherwise it is hard to tell what went wrong.
 
I don't understand your equation for IE. A difference of 6% is a bit large for rounding errors.
 
As I know it to be, it is basically simplifying the circuit using Thevenins Theorem.
Problem is I don't know where to use it.
From the examples I've worked it seems as if I can use this method OR the voltage divider method.
But in some instances, there is a considerate difference in my calculations.
My lecturer is out of office at the moment. So unfortunately I cannot email him.
 

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I do realize that the Thevenins method is for loading effects and the voltage-divider method is for unloaded effects. But I have come across questions where they do not mention whether the circuit is loaded or not.
 
You must inevitably arrive at the same answer, unless you make different or wrong approximations along the way, or through oversight or blunder.
 

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