How Does Charge Injection Affect NPN Transistor Operation?

  • Thread starter Thread starter Pushoam
  • Start date Start date
  • Tags Tags
    Npn Transistor
Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
3 replies · 2K views
Pushoam
Messages
961
Reaction score
53
In a transistor, the base-emitter junction is forward biased while the base-collector junction is reverse biased.
The emitter emits charge carriers.These charge carriers go to the base.
My question is: why don't all of these charges flow as base current since this junction provides low resistance path?
In the book, it is said that since the base is thin, most of the charge carriers( which have come to the base) go to the collector.
Then, my question is why doesn't collector remain negatively charged as the collector junction is highly resistive? Why do these charges flow as a collector current?
 
Last edited:
Engineering news on Phys.org
Once charges are in the narrow base region, they can be attracted towards the battery positive suppying the base, or to the greater battery positive supplying the collector.

I wouldn't say the collector is of highly resistive material. Maybe some tens of ohms.
 
NascentOxygen said:
Maybe some tens of ohms.
In my book, it is said that the collector-base junction has a resistance of the order of 100 k##\Omega##.
 
Pushoam said:
In my book, it is said that the collector-base junction has a resistance of the order of 100 k##\Omega##.
Ah, that's the resistance (a measure of the difficulty of getting through the reverse-biased region) seen by charges originating from the external collector-base circuit, they see a high resistance. But if you arrange some other means to inject charge into the depletion region, then those introduced charges once they're in the depletion region get swept along by the strong potential gradient and to them it's an easy route out (i.e., they see low resistance).