CBSE Class 12-science Answered
how transistor works as an amplifier and switch
pls explain it
i could'nt grasp those viseo sessions
Asked by Sumesh | 04 Feb, 2018, 09:06: PM
Expert Answer
There are two types of transistor (1) npn and (2) pnp. Figure given above shows a typical configuration for an npn junction transistor. The three sections are called the emitter, base and collector. The conduction and valance bands are shown, and only the majority carriers are indicated. In normal operation, as illustrated at right side of the figure, the emitter-base junction is forward biased and base-collector junction is reverse biased, which gives the energy band as shown in figure.
Electrons flow from the heavily doped n-type emitter into the base. Because the base is very narrow, most of these electrons reach the collector, but a few recombine withholes in p-type region. To regain the hole population in the base, electrons from the valance band in the base must leave the transistor through the external circuit as the small base current ib. A small change in the base current ib can result in a large change in the collector current ic. In this configuration , the transistor serves as a current amplifier. The current gain ic/ib is typically around 100.
The whole operation described above is possible only if emitter-base junction is forward biased. if borward bias is removed, there wont be any ic current. Hence by switching on-off the forward bias, ic will become on-off and controlled and transistor act as switch
Answered by Thiyagarajan K | 07 Feb, 2018, 12:28: PM
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