| Aim | To study the characteristics of a common-emitter NPN or PNP transistor and to find out the values of current and voltage gains. |
| Apparatus Required | NPN or PNP transistor DC power supply Resistors Capacitors Ammeter Voltmeter Connecting wires |
| Theory | A transistor is a three-terminal semiconductor device that can amplify or switch electronic signals. A common-emitter configuration is one of the most commonly used configurations for transistor circuits. In this configuration, the emitter terminal is common to both the input and output circuits, and the input signal is applied to the base terminal. The output is taken from the collector terminal. |
| Procedure | Connect the transistor to the DC power supply, resistors, capacitors, ammeter, and voltmeter using connecting wires. Set up a circuit in the common-emitter configuration. Apply a small input voltage to the base terminal and measure the corresponding output voltage across the collector and emitter terminals. Vary the input voltage and measure the corresponding output voltage. Calculate the current gain and voltage gain of the transistor using the formulae: Current gain (hfe) = IC / IB Voltage gain (Av) = Vout / Vin where IC is the collector current, IB is the base current, Vout is the output voltage, and Vin is the input voltage. Calculate the input resistance and output resistance of the transistor using the formulae: Input resistance = Vin / IB Output resistance = Vout / IC Tabulate the values of current gain, voltage gain, input resistance, and output resistance. |
| Observation and Result | Observation: The output voltage increases as the input voltage increases, but the output voltage reaches saturation at a certain input voltage. The current gain and voltage gain of the transistor can be calculated from the measured values of IC, IB, Vout, and Vin. The input resistance and output resistance of the transistor can also be calculated from the measured values. Result: The characteristics of a common-emitter NPN or PNP transistor have been successfully studied. The values of current gain, voltage gain, input resistance, and output resistance have been calculated. The results of the experiment demonstrate the amplification and switching properties of a transistor in the common-emitter configuration. |
