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Thursday, 17 November 2011

Biasing and Working of NPN Transistors

Due to forward biasing of emitter-base junction, majority carriers (Electrons) flow towards base. A big amount of electrons cross the junction and enter the base. As the base is lightly doped, so a small amount (2 to 5 percent) of electrons recombine with holes in the base and almost more than 95 percent electrons come under the effect of positively charged collector and enter the collector. This is possible due to attraction of collector voltage.
As collector-base junction is reverse biased, so electrons cannot flow from collector to base due to high resistance, infect, electrons always flow from base to collector.
 Thus due to diffusion and collection of electrons (provided by emitter) in the collector-base junction, the flow of electronic current starts. The direction shown in figure shows the flow of conventional current.
This should be kept in mind that the transistor will not conduct unless its emitter-base junction is forward biased.

Biasing of NPN Transistor

Biasing of NPN Transistor (Symbol, Circuit Diagram)



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