The bipolar junction transistor (the English Bipolar Junction Transistor or their initials, BJT) is an electronic device solid consisting of two PN junctions close together, which controls the passage of current through their terminals. Bipolar transistors are generally used in analog electronics . Also in some applications of digital electronic as or BICMOS TTL technology. A bipolar junction transistor consists of two PN Unions on a single crystal semiconductor, separated by a very narrow region. Are thus formed three regions:
- ISSUER: That differs from the other two to be heavily doped , behaving like a metal.
- BASE: The middle, very close, which separates the emitter from the collector.
- COLLECTOR: Of much greater extent.
OPERATION In a typical configuration, the emitter-base directly and is polarized in the base-collector reverse. Due to thermal agitation of charge carriers can cross the barrier emitter of emitter-base potential and reach the base. In turn, almost all carriers that arrived are driven by the electric field between the base and collector.
The core region of a transistor must be constructively thin so that carriers can diffuse through it in much less time than the minority carrier lifetime of semiconductor, to minimize the percentage carriers that recombine before reaching the base-collector junction. The thickness of the base should be less than the width of diffusion of electrons.
- CONTROL VOLTAGE, CHARGE AND CURRENT
In analog circuit design, power control is used because it is approximately linear. This means that the collector current is approximately β times the base current. Some circuits can be designed assuming the base-emitter voltage is approximately constant, and that the collector current is β times the base current. However, to design circuits using BJT accurately and reliably, it requires the use of mathematical models of the transistor as the Ebers-Moll model .
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