BJT Biasing Formulas

[ABEL DANIEL]

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?

 

[KlausST]

Hi,

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

Klaus

 

[FvM]

dont we need to find the region of operation(active,cutoff and sat)first,before applying these formulas?

Yes, you do. In the present example, the transistor is in saturation, thus beta isn't valid.

 

[PRIYADHARSHINI PALANISAMY]

hi
this is the basic question ..how can we find the region of operation?

 

[peeyushsigma]

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.