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Circuits Elements and Functions of Practical Transistor Amplifier


Practical Transistor Amplifier

The below fig shows a practical single stage transistor amplifier. The various circuit elements and their functions are described below.

Practical Transistor Amplifier

1.       Biasing Circuit: The resistor R1, R2, andRE form the biasing and stabilization circuit.
2.       Input Capacitor Cin: An electrolytic capacitor Cinis used to couple the signal to the base of the transistor. The capacitor Cinallows only a.c. signal to flow but isolates the signal source from R2. If it is not used, the signal source resistance will come across R2and thus change the bias. Typical value of Cin is 10µF.
3.       Emitter Bypass Capacitor CE: An emitter bypass capacitor CE is used in parallel with RE to provide a low reactance path to the amplified a.c. signal. If it is not used, then amplified a.c. signal flowing through RE will cause a voltage drop across it, thereby reducing the output voltage. Typical value of CE is 100µF.

4.       Coupling Capacitor CC: The coupling capacitor CCcouples one stage of amplifier to the next stage. If it is not used, the bias conditions of the next stage will be drastically changed due to parallel with the resistance R1 of the biasing network of the next stage. Thereby it alters the biasing conditions of next stage. The coupling capacitor CC isolates the d.c. of one stage from the next stage, but allows the passage of a.c. signal. Typical value of CC is 10µF.

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