A PNP Bipolar Junction Transistor (BJT) is a type of transistor where two p-type semiconductor layers surround an n-type layer (hence, PNP). Like the NPN transistor, it has three terminals: Emitter (E), Base (B), and Collector (C).
How PNP BJT works:
1. Emitter:
The emitter is heavily doped to inject holes (positive charge carriers) into the base.
2. Base:
The base is thin and lightly doped with n-type material. When a small negative voltage is applied between the base and the emitter (V_BE), the base-emitter junction is forward biased, allowing holes to flow from the emitter into the base.
3. Collector:
The collector is moderately doped. A larger negative voltage between the collector and emitter (V_CE) pulls the holes from the base to the collector, creating a current flow.
Current Flow:
- Base current (I_B):
A small current flows out of the base.
- Collector current (I_C):
A larger current flows from the emitter to the collector, controlled by the base current.
- Emitter current (I_E):
The total current flowing from the emitter (I_E = I_C + I_B).
Key Concept:
- In a PNP transistor, the current flows when the base is more negative than the emitter. A small current exiting the base allows a larger current to flow from the emitter to the collector. The PNP transistor "turns on" when a small negative voltage is applied to the base, allowing current to flow in the opposite direction compared to an NPN transistor (from emitter to collector).
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