Vol III - BJT - Bias Calculations missing assumption?

Thread Starter

deBooglel

Joined Nov 26, 2012
1
Hi there,

I could be wrong but in the section for the Bias Calculations using the collector feedback method the following is stated based on KVL:

Vcc-IcRc-IbRb-Vbe = 0

I think technically the voltage across Rc is (Ic + Ib)Rc, but as Ic is much much greater than Ib we can assume Ib is negligible. BUT this assumption was not stated and therefore technically the KVL equation is wrong!

I might be wrong though!

D
 

Georacer

Joined Nov 25, 2009
5,182
The assumption is stated, even if not explicitly. You can read \(I_c=(\beta +1) I_b \approx \beta I_c\)

I guess it could be more clear, but then again, space and coherence is an issue.
 

tshuck

Joined Oct 18, 2012
3,534
I think technically the voltage across Rc is (Ic + Ib)Rc, but as Ic is much much greater than Ib we can assume Ib is negligible. BUT this assumption was not stated and therefore technically the KVL equation is wrong!
D
Look at line 1: \(I_{C}\approx I_{E}\)
That is your assumption...
 
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