A PNP bipolar junction transistor has three semiconductor layers with two P-type regions and one N-type region, each with a specific role:
- Emitter: Supplies majority charge carriers, heavily doped, and forward biased with respect to the base.
- Collector: Collects most of the charge carriers from the emitter, moderately doped, and always reverse biased.
- Base: Splits into the input circuit with the emitter (forward biased, low resistance) and the output circuit with the collector (reverse biased, higher resistance). The base is lightly doped and thin, allowing it to control the majority of charge carriers.
Depletion regions form at the emitter-base and base-collector junctions.
In a PNP transistor, the emitter and collector are P-type and heavily doped, while the base is N-type and lightly doped. This makes the depletion region go into the N-type layer. PNP transistors use “holes” as the main charge carriers, with electrons being less important. Holes come out of the emitter and go to the collector. The flow of current in a PNP transistor is controlled by the base, and it goes in the opposite direction. The emitter releases holes, and the collector gathers them. The base has some free electrons, but it’s not packed with them because it’s lightly doped. So, there are fewer free electrons in the base region.
- PNP transistors are used to source current, i.e. current flows out of the collector.
- PNP transistors are used as switches.
- These are used in the amplifying circuits.
- PNP transistors are used when we need to turn off something by pushing a button. i.e. emergency shutdown.
- Used in Darlington pair circuits.
- Used in matched pair circuits to produce continuous power.
- Used in heavy motors to control current flow.
- Used in robotic applications.
- 1 x PNP Transistor