BJT amplifier

Jony130

Joined Feb 17, 2009
5,488
Today I don't have the time to check your solution. But here is my solution
Ie = ( 9 - 0.7)/(5K/181 + 0.5K) = 15.73mA

Av = Rin/(Rs + Rin) * (RE||RL)/(re + RE||RL) = 4.36/(1 +4.36) * 187.5/(1.652 + 187.5) = 0.806V/V

Rin = R1||R2||Rib = 4.36K ohm

Rib = (Hfe +1) * (re +RE||RL) = 34.23k ohm

re = 26mV/Ie = 1.65 ohm
 

Thread Starter

full

Joined May 3, 2014
225
Today I don't have the time to check your solution. But here is my solution
Ie = ( 9 - 0.7)/(5K/181 + 0.5K) = 15.73mA

Av = Rin/(Rs + Rin) * (RE||RL)/(re + RE||RL) = 4.36/(1 +4.36) * 187.5/(1.652 + 187.5) = 0.806V/V

Rin = R1||R2||Rib = 4.36K ohm

Rib = (Hfe +1) * (re +RE||RL) = 34.23k ohm

re = 26mV/Ie = 1.65 ohm
thanks sir , I know you are not have time and your time are very important.......
 

Thread Starter

full

Joined May 3, 2014
225
Well you made a mistake R1 is 250k not 225K. Because Vth = 1.1538V not 1.25V.
Ib = 3.48329μA; Ic = 417.995μA; Ie = 421.478μA.

As for the gain

Av = Rc/(re + RE) * (Rib||Rth)/(Rs + Rib||Rth) = 8.46 * 0.985 =8.3V/V
re = 26mV/Ic
Rib = ( β+1 )*(re + RE) = 80kΩ
Rth = R1||R2 = 57.7kΩ

And for BJT we have Ie = Ib + Ic but as you know Ic = Ib*β. So we have Ie = Ib + β*Ib = (β +1)*Ib.
I think the Av in negative true?
Av=(Vo/Vs) = (-B*Rc/r-pi+(1+B)*Re)(Ri/Ri+Rs)
Ri = Rth || Rib
thanks
 
Last edited:

Thread Starter

full

Joined May 3, 2014
225
full.PNG
the Vth is zero?
or Vth=(v2/V1+V2)*{ (Vee)-(vcc) }?
Vth=(250k/175k+250k)*{ (9)-(-9) }
Vth= 10.6v
thanks
 

Jony130

Joined Feb 17, 2009
5,488
I think the Av in negative true?
Av=(Vo/Vs) = (-B*Rc/r-pi+(1+B)*Re)(Ri/Ri+Rs)
Ri = Rth || Rib
thanks
Yes, the voltage gain for CE amplifier is negative. But we usually forget about this "minus" sign. Because this "minus" only inform us that our amplifier output is 180° out of phase with its input nothing more.

View attachment 74666
the Vth is zero?
or Vth=(v2/V1+V2)*{ (Vee)-(vcc) }?
Vth=(250k/175k+250k)*{ (9)-(-9) }
Vth= 10.6v
thanks
You have Vcc upside down in full2 pic.
And Vth = 1.6V or 10.6V see this two diagrams
3.PNG
 
Last edited:

Thread Starter

full

Joined May 3, 2014
225
Yes, the voltage gain for CE amplifier is negative. But we usually forget about this "minus" sign. Because this "minus" only inform us that our amplifier output is 180° out of phase with its input nothing more.


You have Vcc upside down in full2 pic.
And Vth = 1.6V or 10.6V see this two diagrams

View attachment 74673
is mean the analysis for Vth=10.6

Vee - VRe - Vbe - VRth - Vth =0 ( emitter-base )
(Vee=18)

Vee - VRe - Vce - VRc=0 (emitter-Collier) true?

please see this :
http://forum.allaboutcircuits.com/threads/analyses-for-bipolar-junction-transistor.102779/

thanks sir for help me
 

Jony130

Joined Feb 17, 2009
5,488
Wrong, the voltage is potential difference. So V+ = +9 and V- = -9V
So the voltage between V+ and V- is equal to +9V - (-9V) = 18V
 
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