What is a PNP Transistor ?
A PNP transistor is a type of bipolar junction transistor (BJT) where the current flows from the emitter to the collector when the base is held at a voltage lower than the emitter. It consists of three regions of semiconductor material:
- Emitter (P-type): Heavily doped to emit holes (majority carriers).
- Base (N-type): Thin and lightly doped, it controls the flow of holes.
- Collector (P-type): Moderately doped and larger than the emitter to collect carriers.
How a PNP Transistor Works
- Biasing: For a PNP transistor to conduct, the emitter must be at a higher potential than the base. Typically:
- The emitter-base junction is forward-biased.
- The base-collector junction is reverse-biased.
- Operation:
- When a small current flows out of the base (opposite to an NPN transistor where it flows in), it allows a larger current to flow from the emitter to the collector.
- Holes are the majority carriers in PNP transistors, unlike electrons in NPN transistors.
Symbol
The symbol of a PNP transistor is similar to that of an NPN transistor but with the arrow pointing inward toward the base, indicating the direction of conventional current flow from emitter to base.
Applications
- Used in switching circuits.
- Part of push-pull amplifier circuits.
- Suitable for high-side switching in power applications.
Key Differences from NPN Transistor
- Current Flow: In a PNP, the current flows from emitter to collector; in an NPN, it flows from collector to emitter.
- Biasing: The emitter of a PNP is more positive than the base, while in an NPN, the emitter is more negative.