Bipolar junction transistor - Wikipedia, the free encyclopedia

Bipolar junction transistor - Wikipedia, the free encyclopedia

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 Bipolar junction transistor From Wikipedia, the free encyclopedia (Redirected from BJT ) Jump to: navigation , search BJT redirects here. For the Japanese language proficiency test, see Business Japanese Proficiency Test . A bipolar junction transistor ( BJT ) is a type of transistor . It is a three-terminal device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons and holes . Although a small part of the transistor current is due to the flow of majority carriers , most of the transistor current is due to the flow of minority carriers and so BJTs are classified as 'minority-carrier' devices. PNP NPN The schematic symbols for PNP- and NPN-type BJTs.
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Contents 1 Introdu ction 1 . 1 V o l t a g e , c u r r e n t , a n d c h a r g e c o n t r o l 1 . 2 T r a n
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[ edit ] Introduction NPN BJT with forward-biased E–B junction and reverse-biased B–C junction An NPN transistor can be considered as two diodes with a shared anode region. In typical operation, the emitter–base junction is forward biased and the base–collector junction is reverse biased . In an NPN transistor, for example, when a positive voltage is applied to the base–emitter junction, the equilibrium between thermally generated carriers and the repelling electric field of the depletion region becomes unbalanced, allowing thermally excited electrons to inject into the base region. These electrons wander (or " diffuse ") through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type which would make holes the majority carrier in the base. The base region of the transistor must be made thin, so that carriers can diffuse across it in much less time than the semiconductor's minority carrier lifetime, to minimize the percentage of carriers that recombine before reaching the collector–base junction. To ensure this, the thickness of the base is much less than the diffusion length of the electrons. The collector–base junction is reverse-biased, so little electron injection occurs from the collector to the base, but electrons that diffuse through the base towards the collector are swept into the collector by the electric field in the depletion region of the collector–base junction. [ edit ] Voltage, current, and charge control The collector–emitter current can be viewed as being controlled by the base–emitter current (current control), or by the base–emitter voltage (voltage control). These views are related by the current–voltage relation of the base–emitter junction, which is just the usual exponential current–voltage curve of a p-n junction (diode).
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This note was uploaded on 09/29/2010 for the course GENERAL AR ECE 250 taught by Professor Drcapps during the Spring '10 term at N.C. State.

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Bipolar junction transistor - Wikipedia, the free encyclopedia

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