How Does Charge Injection Affect NPN Transistor Operation?

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Discussion Overview

The discussion revolves around the operation of NPN transistors, specifically focusing on the effects of charge injection on the behavior of charge carriers within the transistor's base and collector regions. Participants explore the dynamics of charge flow, resistance in the collector-base junction, and the implications of these factors on transistor operation.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why not all charge carriers that enter the base flow as base current, given the low resistance path, and why the collector does not remain negatively charged despite being highly resistive.
  • Another participant suggests that once charges are in the narrow base region, they can be attracted to either the base or the collector, challenging the notion of the collector being highly resistive.
  • A different participant asserts that the collector-base junction has a resistance on the order of 100 kΩ, indicating a significant resistance to external charge flow.
  • One participant clarifies that the stated resistance reflects the difficulty for charges from the external circuit to traverse the reverse-biased region, but injected charges in the depletion region may experience a low resistance path due to the strong potential gradient.

Areas of Agreement / Disagreement

Participants express differing views on the resistance of the collector and the implications for charge flow, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

There are unresolved assumptions regarding the definitions of resistance in the context of charge injection and the behavior of charge carriers in the transistor's regions.

Pushoam
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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?
 
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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).
 

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