Transistor Biasing

The proper flow of zero signal collector current and the maintenance of proper collector-emitter voltage during the passage of signal as known Transistor Biasing.

The process of raising the strength of a weak signal with out any change in its general shape is known as faithful amplification.

The theory of transistors reveals that it will function properly if input circuit remains forward biased and output circuit remains reverse biased at all times. This is then the key factor for achieving faithful amplification .To ensure the three basic condition :-

(I) Proper zero signal collector current. (II) Minimum proper base -emitter voltage at any instant. (III) Minimum proper collector-emitter voltage at any instant.

I) proper zero signal collector current:-. Consider an n-p-n transistor circuit shown below 1(a). During the positive half cycle of the signal , base is positive w.r.t emitter and hence base emitter junction is forward biased. This will cause a base current and much larger collector current to flow in the circuit. The result is the positive half cycle of the signal is amplified in the collector as shown .However , during the negative half cycle of the signal, base- emitter junction is reverse biased and hence no current flows in the circuit. The result is that there is no output due to negative half cycle of the signal . Thus we shall get an amplified output of the signal with its negative half cycles completely cut off which unfaithful amplification.

Now, introduce a battery source V

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