Electrical Engineering ⇒ Topic : Input Characteristics

Input Characteristics

The curve between the input current I_B (base current) and input voltage V_BE (base-emitter voltage) gives the input characteristic for CE configuration. The base current is taken along the Y-axis and the base-emitter voltage is taken along the X-axis. Figure (a) shows the input characteristics of a typical transistor in common emitter configuration.

The following conclusions can be drawn from these characteristics:

The base current increases rapidly with a small increase in base-emitter voltage after the cut-in voltage. Therefore, the dynamic input resistance is very small in CE configuration

           Figure (a) Input characteristics of the transistor in CE configuration.

The base current increases as collector-emitter voltage is decreased for a fixed value of base-emitter voltage. A large reverse bias at collector-base P-N junction occurs for a larger value of V_CE. This increases the depletion region and reduces the effective width of the base. Therefore, there are fewer recombinations in the base region. Hence, base current is reduced