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 R_1, R_2, and R_E form the biasing and stabilization circuit.

2.       Input Capacitor C_in: An electrolytic capacitor C_in is used to couple the signal to the base of the transistor. The capacitor C_in allows 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 R₂ and thus change the bias. Typical value of C_in is 10µF.

3.       Emitter Bypass Capacitor C_E: An emitter bypass capacitor C_E is used in parallel with R_E to provide a low reactance path to the amplified a.c. signal. If it is not used, then amplified a.c. signal flowing through R_E will cause a voltage drop across it, thereby reducing the output voltage. Typical value of C_E is 100µF.

4.       Coupling Capacitor C_C: The coupling capacitor C_C couples 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 C_C isolates the d.c. of one stage from the next stage, but allows the passage of a.c. signal. Typical value of C_C is 10µF.