Types of transistors

An NPN transistor is a semiconductor device with three distinct areas: a P-region sandwiched between two N-regions. In active mode, VCB reverse-biases the collector-base junction while VBE forward-biases the emitter-base junction, causing electrons in the emitter to diffuse through the base into the emitter.
In an NPN transistor, a positive voltage is given to the collector terminal to produce a current flow from the collector to the emitter. In a PNP transistor, a positive voltage is given to the emitter terminal to produce current flow from the emitter to collector.