Bipolar junction transistor
A bipolar junction transistor (BJT or bipolar transistor) is a type of transistor that relies on the contact of two types of semiconductor in order for it to work. BJTs can be used as amplifiers, switches, or in oscillators. BJTs can be found either on their own, or in large numbers as parts of integrated circuits.[1]
They are named bipolar transistors because their operation involves both electrons and holes.
The current gained is measured in hfe, Forward Current Gain. Typical amount can be between 200-350.
Bipolar Junction Transistor Media
Typical applications, Three- (or more) terminal devices: PNP transistor (also PNIP transistor, if omitting the intrinsic region will not result in ambiguity)
Typical applications, Three- (or more) terminal devices: NPN transistor (also NPIN transistor, if omitting the intrinsic region will not result in ambiguity)
3D model of a TO-92 package, commonly used for small bipolar transistors
NPN BJT with forward-biased B–E junction and reverse-biased B–C junction
Simplified cross section of a planar NPN bipolar junction transistor
Die of a 2N2222 NPN transistor: the NPN materials are made in layers with the collector at the bottom. Bond wires connect metalisation on the base to the left lead, and emitter to the right. The collector is connected to the can with a third external lead..
Symbol for NPN bipolar transistor with current flow direction
Structure and use of NPN transistor; arrow according to schematic
Band diagram for NPN transistor at equilibrium
Band diagram for NPN transistor in active mode, showing injection of electrons from emitter to base, and their overshoot into the collector
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Other websites
- Simulation of a BJT in the Common Emitter Circuit Archived 2010-07-16 at the Wayback Machine