Question about BJT amplifier configuration

[hayowazzup]

Hi all,
just wondering if the two bjt configurations work the same?
1. darlington pair
2. common emitter + emitter follower + common emitter

 

[KerimF]

Re: BJT Amplifier config

I am afraid the second configuration is not fully clear. Perhaps it is just me.

 

[hayowazzup]

Re: BJT Amplifier config

the second one is amplifiers with a buffer in between

 

[KerimF]

Re: BJT Amplifier config

You mean 3 transistors?... I hope you have a link for its pic.
I am sure, the circuit of interest is simple and clear to you but to those who have seen thousands of circuits, it is hard for them to be 100% sure of all its details from your description.
Sorry... perhaps some others have a better idea of it.

 

[LvW]

Re: BJT Amplifier config

Hi all,
just wondering if the two bjt configurations work the same?
1. darlington pair
2. common emitter + emitter follower + common emitter

The same resp. similar operation? Of course, not.

* The darlington pair works like a single transistor with h21=h21,1*h21,2 but with an overall transconductance g=0.5*g2.
Transconductance g2 (2nd transistor) is determined by Ic,2. (Very often, this is forgotten believing that a high current gain automatically leads to high voltage gain)
* two emitter stages allow more voltage gain. I am not sure if the buffer in between makes really sense.