Specialized types are used for high voltage switches, for radio-frequency amplifiers, or for switching heavy currents.īJTs exist as PNP and NPN types, based on the doping types of the three main terminal regions.
Bipolar transistors are still used for amplification of signals, switching, and in digital circuits. Hundreds of bipolar junction transistors can be made in one circuit at very low cost.īipolar transistor integrated circuits were the main active devices of a generation of mainframe and mini computers, but most computer systems now use integrated circuits relying on field effect transistors. Diffused transistors, along with other components, are elements of integrated circuits for analog and digital functions. The superior predictability and performance of junction transistors soon displaced the original point-contact transistor. The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between two other terminals, making the device capable of amplification or switching.īJT uses two junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A Bipolar Junction Transistor (BJT) ( discrete component)is a type of transistor that uses both electrons and electron holes as charge carriers.
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