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BJT Biasing Formulas

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ABEL DANIEL

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For this i have have a SOLUTION.But i have a doubt in the solution:
Here,base current is found by applying KVL to i/p loop and then

Then Ic =βIb and then Ie=gamma Ib=(β+1)Ib
So Rc is found by applying KVL to output loop

My question is, can we apply formulas like Ic=alpha* Ie(like one,that we used here),Ic=βIb and Ie=gamma*Ib,blindly in every problem;dont we need to find the region of operation(active,cutoff and sat)first,before applying these formulas?
 
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Hi,

My hint: What goes in must come out. Ib and Ic goes in, Ie goes out. ==> Ie = Ib + Ic.

Klaus
 

dont we need to find the region of operation(active,cutoff and sat)first,before applying these formulas?
Click to expand...
Yes, you do. In the present example, the transistor is in saturation, thus beta isn't valid.
 

you can not apply these formulas blindly ...here is some points to remember...

1. firstly suppose transistor is in active region and find out the base current.
2. apply Ic =βIb.
3. find Icsat= (Vcc-0.2)/Rc.
4. If Ic< Icsat. then Transistor is in active region otherwise if Ic>=Icsat then it is in saturation region.
 
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