Common Collector question

[AMSA84]

Hi guys,

Can someone explain how in the Rout expression for the common collector transistor the Rs comes divided by (1+β)? I tried to solve by definition, using the Vx at the output node and I got an expression which size was similar to a train :lol:

 

[andre_luis]

Did you see that ?
https://www.ittc.ku.edu/~jstiles/41...e BJT Amps/The Common Collector Amplifier.doc

 

[D.A.(Tony)Stewart]

After you do the math, my rule of thumb is

Unity voltage gain

As input impedance is raise by ~hFE *Re
and output impedance is lowered by ~hFE,

AC coupled load current can never exceed the DC emitter current and starve the junction of current drain. i.e. AC coupled load R must be any higher value than Re.

 

[AMSA84]

Andre, thank you for the reference. However they use the T-Model instead of the Pi-Model. I was looking to solve the problem using the Pi-Model. Do you have any idea on how to do this?

Regards.