Electron flow in common base and common collector transistor configurations

Thread Starter

Doubtician

Joined Mar 19, 2022
11
Could somebody explain the working of common base and common collector transistor configurations?How do the electrons begin flowing in these configurations?
 

Thread Starter

Doubtician

Joined Mar 19, 2022
11
They flow due to the applied signal a bias voltages.
Not sure I understand the word "how" in this context (?).
By 'how', i meant how the input voltage forces the electron flow ?Like , in CE configuration,the base input voltage forces a large a no.of electrons from emitter region to flow to p region (base)where some recombine and rest goes to the n region(collector),where the positive voltage attracts them to the collector battery terminal thereby constituting the collector current.How does this work with the CB and CC configurations?
 

Delta Prime

Joined Nov 15, 2019
1,326

Delta Prime

Joined Nov 15, 2019
1,326
Yeah,sorry about that partner, but I must say you did ask the right question. With my current knowledge base I can only explain it two ways but I believe the prerequisite is to explain it three different ways.
Again my apologies.
 

LvW

Joined Jun 13, 2013
1,438
By 'how', i meant how the input voltage forces the electron flow ?Like , in CE configuration,the base input voltage forces a large a no.of electrons from emitter region to flow to p region (base)where some recombine and rest goes to the n region(collector),where the positive voltage attracts them to the collector battery terminal thereby constituting the collector current.How does this work with the CB and CC configurations?
Your wording "the base input voltage forces...." is somewhat misleading and may be one source of misunderstanding.
Instead, it is the voltage Vbe between base and emitter which allows (not "forces") the movement of charged carriers from the emitter through the base region to the collector .
This happens because the DC voltage Vbe works against the diffusion barrier across the pn-junction.
For Vbe=(0.6---0.7)V this barrier nearly disappears and acts no longer as a brake for the electrons.
This is exactly the same effect which can also be observed for each pn-diode.
When you realize how a pn-diode works, it is no problem to understand what a BJT does.
Only very few electrons (a nearly fixed percentage) recombine in this area and form the base current (as an unavoidable side effect).
The majority now is able to cross this very thin region and will be atracted by the collector voltage.

Of course, exactly the same happens in CB and CC configurations. The BJT does not change its working principle.
The only difference is the node where the input signal must be injected (E in the CB configuration) or where the output signal is available (E in CC configuration).
 
Last edited:

BobTPH

Joined Jun 5, 2013
4,897
What is the purpose of your question? Are you studying solid state physics or electronics? If the latter, the answer will not help you use a transistor in a circuit.

Bob
 
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