An NPN Bipolar Junction Transistor (BJT) is a type of BJT where the transistor is made up of two n-type semiconductor layers surrounding a p-type layer (hence, NPN). It has three terminals: Emitter (E), Base (B), and Collector (C).
How NPN BJT works:
1. Emitter:
The emitter is heavily doped to inject electrons into the base.
2. Base:
The base is thin and lightly doped, allowing only a small amount of holes. When a small positive voltage is applied between the base and the emitter (V_BE), the base-emitter junction is forward biased, allowing electrons to flow from the emitter into the base.
3. Collector:
The collector is moderately doped. A larger voltage between the collector and emitter (V_CE) pulls the electrons from the base to the collector, creating a current flow.
Current Flow:
- Base current (I_B):
A small current that flows into the base.
- Collector current (I_C):
A larger current flows from the collector to the emitter, controlled by the base current.
- Emitter current (I_E):
The total current flowing from the emitter (I_E = I_C + I_B).
In an NPN transistor, a small current at the base controls a larger current between the collector and emitter, allowing it to function as an amplifier or switch.
Key Concept:
- The NPN transistor turns "on" when a small positive voltage is applied to the base, allowing current to flow from the collector to the emitter.
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