Transistor Characteristics | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

In physics, the graph representing the relationships between the current and the voltage of any transistor of any configuration is called Transistor Characteristics. In this session, let us learn the transistor characteristics in detail. 

Characteristics of Transistors:

Any two-port network which is analogous to transistor configuration circuits can be analyzed using three types of characteristic curves. They are

• Input Characteristics: The curve describes the changes in the values of input current with respect to the values of input voltage, keeping the output voltage constant.
• Output Characteristics: The curve is obtained by plotting the output current against output voltage, keeping the input current constant.
• Current Transfer Characteristics: This characteristic curve describes the variation of output current in accordance with the input current, keeping the output voltage constant.

Configurations:

Any transistor circuit can be designed using three types of configuration. Three configurations of the transistor are based on the connection of the transistor terminal. The three types of transistor circuit configurations are:

• Common Emitter Transistor
• Common Base Transistor
• Common Collector Transistor(emitter follower).

Common Emitter (CE) Configuration of Transistor

The configuration in which the emitter is connected between the collector and base is known as a common emitter configuration.

Input characteristics are the relationship between the input current and the input voltage keeping output voltage constant. Here the input current is the base current IB, input voltage is base emitter voltage VBE and the output voltage is collector emitter voltage VCE.

First the output voltage VCE is kept at zero and the input voltage VBE is gradually increased and the input current IB is noted. Then again the output voltage VCE is increased like 10V, 20V and kept constant and by increasing the input voltage VBE, the input current IB is noted.

From the results it is observed that when the input voltage VBE is increased initially there is no current produced, further when it is increased the input current IB increases steeply. When the output voltage VCE is further increased the curve shifts right side.

Output characteristics is the relationship between the output current and the output voltage keeping input current constant. Here the values of output current IC and the output voltage VCE is noted keeping input current IB constant.

In active region when the output voltage is increased there is very slight change in the output voltage. The curve looks almost flat in the active region. Cut off region is the region where the input current is below zero. When both the junctions are forward biased, it is in saturation region.

Transfer Characteristics. The variation of Emitter current(IE) with the base current(IB), keeping Collector-Emitter voltage(VCE) constant. 

Common Base (CB) Configuration of Transistor

In CB Configuration, the base terminal of the transistor will be connected common between the output and the input terminals.

Common Collector (CC) Configuration of Transistor

In CC Configuration, the Collector terminal of the transistor will be connected common between the output and the input terminals.

Characteristics curves

• Input Characteristics – To determine the i/p characteristics Vce is kept at a suitable fixed value. The base collector voltage Vbc is increased in equal steps and the corresponding increase in I_b is noted.

• Output Characteristics – The Curve drawn between emitter current and collector-emitter voltage for a given value of current is known as output characteristics. Output characteristics of CC at constant: