common emitter circuit design

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

  1. weije1986

    Thread Starter Member

    Apr 19, 2008
    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 .. :D
  2. Caveman

    Senior Member

    Apr 15, 2008
    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
    meaning that i should use Vcc/2 = IcRc in order to calculate value of Rc ?
    should be ok ...
    Thanks alot