Solving for Vc, Vb, Ve, Ib, Ic and Ie

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SUMMARY

The discussion focuses on calculating the voltages and currents in a transistor circuit, specifically Vc, Vb, Ve, Ib, Ic, and Ie, with Vbe set at 0.7V. The calculations yield Vb = 3.75V, Ve = 3.05V, and Ie = 0.305A, indicating that the circuit is saturated since Ie exceeds the maximum collector current Icmax of 9.9mA. The participants suggest using Thévenin's theorem for more accurate results and recommend labeling resistors and deriving equations systematically to avoid saturation errors.

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  • Basic algebra for solving simultaneous equations
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Homework Statement


Find Vc, Vb, Ve, Ib, Ic, and Ie
Vbe is 0.7V

upload_2016-10-31_12-41-50.png


Homework Equations


KVL

The Attempt at a Solution


Vb = (10*30k)/(80k) = 3.75V
Ve = Vb-Vbe = 3.05V
Ie = Ve/Re = 0.305A
Icmax = 10/(1010) = 9.9mA
Ie is much greater than 9.9mA, so this circuit is saturated. Is this correct?
 

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eehelp150 said:
Vb = (10*30k)/(80k) = 3.75V
This is true iff the base current is zero or negligible.

It is better to apply Thévenin and say VB = 3.75 – IB×30k||50k

Q still turns out to be saturated, yes.
 
1. Substitute labels for the resistors, like R1, R2 etc. Substitute actual values only at the end.
2. Write Σi = 0 at the base and emitter junctions. Let Ve = Vb - 0.75V. Gives you 4 independent equations in 4 unknowns.
3. Assume no saturation and solve for ib, Vb, Ve and Vc. If Vc turns out to be < Ve your equations were invalid and you have saturation.
 

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