Electrical Engineering ⇒ Topic : Input Characteristics
The curve between the input current IB (base current) and input voltage VBE (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 VCE. 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
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