Calculating R with Beta in a Circuit

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Homework Help Overview

The discussion revolves around a circuit analysis problem where the original poster attempts to calculate the resistance R given a specific current (I=2mA) and a transistor parameter (Beta=200). The context involves understanding the role of Beta in the circuit's behavior.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster discusses their initial thoughts on voltage calculations and the relationship between currents in the circuit. They express confusion about the relevance of Beta and question how it influences the calculation of Ib and Ic. Other participants inquire about the source of the base current and its implications on current symmetry in the circuit.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the circuit's behavior and questioning the assumptions regarding current flow and symmetry. Some guidance has been offered regarding the roles of various currents, but no consensus has been reached on the implications of Beta or the calculation of R.

Contextual Notes

Participants are grappling with the basic principles of transistor operation and the implications of Beta on current relationships. There is a noted uncertainty about the circuit's configuration and the assumptions made regarding current paths.

Cocoleia
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Homework Statement


I have this circuit
upload_2017-10-7_19-46-30.png

Where I have to find R given that I=2mA, and Beta =200

Homework Equations


Ic=Beta Ib
Ie = Ic+Ib

The Attempt at a Solution


I would have thought that the voltage Vb would be -9.3V, since we have Vbe = 0.7 and at the bottom we are given -10V. Then I would just use this voltage along with the ground, and the current I is also the current going through the resistor (since it is a current mirror) and then find R=4.65kohm. But then, the second question is how would R change is beta is 100.

I don't see what role Beta plays. Maybe I am just tired, this is a really basic circuit. I don't see the point in finding Ib with beta and Ic. We could then find Ie, but I also don't see how this helps. I just don't know how to use this beta.

Thanks,
 
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Where would the base current come from if the currents on both sides would be identical?
 
mfb said:
Where would the base current come from if the currents on both sides would be identical?
upload_2017-10-7_20-0-2.png

Where I drew the red. So does that mean the current in the branch that connects B and C in the transistor in the left is 0 or ?
 
That's where it goes into the transistor, but where does it come from?
Can you see how this breaks the symmetry?
 
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