Exploring the Role of Charge Injection in the Operation of an NPN Transistor

In summary, the base-emitter junction in a transistor is forward biased while the base-collector junction is reverse biased. The emitter emits charge carriers that go to the base. The book explains that the thin base causes most of the charge carriers to go to the collector. The collector-base junction has a resistance of about 100 k##\Omega##, but this is only seen by charges originating from the external circuit. If charges are injected into the depletion region, they will be easily swept along by the strong potential gradient and flow as a collector current.
  • #1
Pushoam
962
52
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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  • #2
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.
 
  • #3
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##.
 
  • #4
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).
 

Related to Exploring the Role of Charge Injection in the Operation of an NPN Transistor

1. What is an npn transistor?

An npn transistor is a type of semiconductor device that is commonly used as a switch or amplifier in electronic circuits. It is composed of three layers of semiconducting material, with two layers of a negative type (n-type) sandwiching a layer of positive type (p-type).

2. How does an npn transistor work?

An npn transistor works by controlling the flow of electrons between the two n-type layers through the middle p-type layer. When a small current is applied to the middle p-type layer, it creates a larger current flow between the two n-type layers, effectively amplifying the signal.

3. What is the role of the base, collector, and emitter in an npn transistor?

The base, collector, and emitter are the three layers of semiconducting material in an npn transistor. The base controls the flow of electrons between the other two layers, the collector collects the electrons, and the emitter releases the electrons into the circuit.

4. What are the applications of npn transistors?

Npn transistors have a wide range of applications, including as switches in digital circuits, as amplifiers in audio applications, and in power supply circuits. They are also commonly used in computer processors and other electronic devices.

5. How do I test an npn transistor?

To test an npn transistor, you can use a multimeter to measure the resistance between the collector and emitter, and between the base and emitter. A properly functioning npn transistor should have a low resistance between the collector and emitter, and a higher resistance between the base and emitter.

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