What is BJT?
BJT or bipolar junction transistor refers to an electronic device with three terminals made of semiconductors. This device may be used to amplify an electric current or switch applications. A typical example of a BJT would be the combination of silicon and/or germanium to form one PN-junction. And if two signal diodes will be joined together back to back, this will result to two PN junctions linked in series. This series will then have a common P or N terminal, resulting to a three-layer, two-junction, and three-terminal electronic device known as bipolar junction transistor.
Since BJTs consist of three terminals, each of these three terminals is given names to identify one from the other. The terminals are usually labeled as B for base, C for Collector, E for Emitter. In a typical setup, the collector and emitter are doped in different ways so they won’t be able to “inter-change” electrically. The base meanwhile represents the mechanical base for the BJT structure and nowadays these are manufactured thinly to gain reasonable levels of electric current.
In terms of the sequence or arrangement of the N and P type materials, bipolar junction transistors may be called the NPN type or PNP type. As the name suggests, NPN type refers to the BJT structure involving a thin P-type material at the center and representing the base, and this is sandwiched between two N-type materials. The opposite is true with PNP types of bipolar junction transistors. In this setup, the N-type material will be the base and placed in between two regions of P-type materials representing the emitter and collector.
Since bipolar junction transistors only act to amplify electric current, the amount of electric current that flows through the collector circuit will depend on how much electric current is flowing at the base circuit. It’s like the BJT functions as a switch to control current flow in the circuit.