# common emitter circuit design

Discussion in 'Homework Help' started by weije1986, Apr 19, 2008.

1. ### weije1986 Thread Starter Member

Apr 19, 2008
14
0
i am new student of enginnering course . need some help to design a simple common emitter BJT .

Set = Vcc=10V , Ic=1mA , and B=100 .
I need to design value of Rc and Rb that i should use .
input biasing = Vdc = 2.5V from base junction .

Calculation : Vcc = IcRc + Vce .... (1)
when saturation , Vce = 0 , then Rc=10k << correcT ?
if i put Rc as 10k , the circuit will be saturated always ?
i found some website saying that we can assume circuit is working in center of load line if it is in active region .
should i use Vcc=10V,Vce=5V,Ic=0.5mA in equation 1 ?

applying KVL : Vdc = IbRb + Vbe
Rb = 80k .. assume Vbe = 0.7V

Thanks for anyone that help ..

2. ### Caveman Active Member

Apr 15, 2008
471
0
Your saturation questions sound correct. We always used 0.3V as saturation Vce, but it doesn't really matter all that much.

Remember B=Ic/Ib (when not in saturation, which you are not, so this is good).
If you want Ic=1mA, then Ib=Ic/B. Get a base resistor that makes that happen.

Your Ic = 1mA is the DC current, so you want 1mA to get you to the center of the voltage range for maximum swing, so you want Vcc/2 across Rc when the current is 1mA.

Can you take it from there?

3. ### weije1986 Thread Starter Member

Apr 19, 2008
14
0
meaning that i should use Vcc/2 = IcRc in order to calculate value of Rc ?
should be ok ...
Thanks alot