Talha's Physics Academy
Working of Transistor as an Amplifier - Class 12 Physics
Video Lecture
Watch the complete video lecture below to gain a thorough conceptual understanding of how a transistor works as an amplifier.
Transistor as an Amplifier
Basic Principle
A transistor amplifies signals by using a small input current or voltage (at the base) to control a much larger current flow between the collector and emitter, effectively boosting the signal's power, voltage, or current—much like a small valve controlling a large flow of water.
Working of the Transistor Amplifier
In this circuit, the transistor is connected in the common-emitter configuration and is properly biased so that it operates in the active region. When an AC signal is applied to the base through the input capacitor, only the alternating component reaches the base while the DC bias remains unchanged.
- During the Positive Half-Cycle: The base–emitter voltage increases slightly, causing an increase in base current. This small increase in base current results in a much larger increase in collector current. The increased collector current produces a larger voltage drop across the load resistor, causing the collector voltage to decrease.
- During the Negative Half-Cycle: The base–emitter voltage decreases, reducing the base current and hence the collector current. As a result, the voltage drop across the load resistor decreases and the collector voltage increases.
Thus, a small variation in base current produces a large variation in collector voltage. The output signal taken from the collector is therefore an amplified version of the input signal and is inverted in phase by $180^\circ$, demonstrating the working of the transistor as an amplifier.
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