Hi:

I am trying to compute the input impedance of an emitter-follower power amplifier
utilizing a TIP31 transistor using

Rin(base) = hFE (RL + RE' + RE)

and

Rin = R1 || R2 || Rin(base)

R1 = R2 = 165 ohms
RE = 1 ohm
RL = 8 ohms
hFE = 25 minimum

I have the impression that you cannot compute RE' using 37mV / IE as you
would in a small signal application.

Could anyone help me.

Thanks,

David

 

For impedance, not DC dynamic R' -

http://fourier.eng.hmc.edu/e84/lectures/ch4/node9.html

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=0ahUKEwjT3vK38LDbAhUM4oMKHXtMA-MQFghpMAw&url=https://www.pdx.edu/nanogroup/sites/www.pdx.edu.nanogroup/files/2013_Input_output_impedance_9.pdf&usg=AOvVaw0WAFQuNlUYKyoGRVJ0FOzt

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiuj8ml8bDbAhXo64MKHQ1XAcIQFggnMAA&url=https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-071j-introduction-to-electronics-signals-and-measurement-spring-2006/lecture-notes/21_bjt_3.pdf&usg=AOvVaw22Q9JqJXkJ0yEGuy1zTg9v

Regards, Dana.