Characteristics of a Transistor
A transistor is a semiconductor device which is used to switch or amplify electronic signals and electric power. It consists of semiconductor material mostly with at least three terminals for connection to an external circuit.
Transistor characteristics are the plots which represent the relationships between the current and the voltages of a transistor in a particular configuration. By considering the transistor configuration circuits to be analogous to two port networks, then can be analysed using the characteristic curves which can be of the following types:
Output Characteristics: This is a plot of output current versus output voltage with constant input current.
Input Characteristics: These describe the changes in input current with the variation in the values of input voltage keeping the output voltage constant.
Current Transfer Characteristics: This characteristic curve shows the variation of output current in accordance with the input current, keeping output voltage constant.
Electrical properties of a transistor can be described by showing the interrelation between the various voltages and currents. These relationships between voltages and current can be displaced graphically and the curves obtained are known as the transistor characteristic curves.
The characteristics of a junction transistor can be obtained by:
1. Common Emitter Transistor
2. Common Base Transistor
3. Common Collector Transistor.
We discuss only the Common Emitter Characteristics of a junction transistor. The common emitter characteristics can be obtained by studying the graph between the voltage and electric current. The base acts as an input terminal, collector acts as an output terminal and the emitter is earth.
The base – emitter battery is forward biased by the base – emitter junction and the collector emitter battery is reversed biased by the base collector junction. The base current and the collector emitter battery is reversed biased by the base – collector junction. The base current and the collector current is measured by the ammeter and the voltage and is measured by the voltmeter.