Transistor as Amplifier
Category: Analog Circuits
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed and simulated in Proteus 7.10. In this circuit you will learn how to use transistor as an amplifier. The yellow color at oscilloscope shows input signal and blue color shows output signal. The working of this circuit is given below. 1. As discussed in previous circuit (Transistor as Inverter) that transistor name came from transformation of resistor, which means resistance of transistor can be changed. 2. To use transistor as an amplifier you have to do proper biasing that transistor remains in linear range throughout the input signal range. 3. The transistor will turn ON at 0.7V so biasing resistors R2 and R3 should be calculated closed to 0.7V, you can bias at 0.6V. 4. The should be calculated as transistor will conduct when the input signal comes in, otherwise transistor will be closed to turn OFF. 5. As the input voltage rises, the base current of transistor will increase, the resistance of transistor reduces and transistor starts conducting. Therefore, the output will goes towards zero. 6. When the input voltage decreases, the base current of transistor also decreases, the resistance of transistor will start increasing and the transistor will goes towars turn OFF, so the output will goes towards high side. 7. The gain will depend on the transistor manufacturing and it is given in the data sheet of transistor, which Ic = beta(Ib), where beta is the gain of transistor. 8. In this circuit we see that transistor amplifies the input signal but with 180 degree phase shift, because transistor acts like inverter. Application 1. This circuit can be used as signal amplifier. 2. This circuit can be used as audio amplifier. Download these files to perform more experiments.