Mumbai University > FE > Sem 1 > Basic Electrical and Electronics Engineering

Marks: 4 M

Year: Dec 2014

Explanation:

1. After the Outin voltage $I_B \uparrow$ rapidly with small increase in $V_{BE} = \gt$ The dynamic input resistance $r_1$ is small in CE configuration.

   It is given by $r_1=\dfrac{\Delta V_{BE}}{I_B} V_{CE} = constant$

   Shown in above figure

   The value of $r_1$ is typically 1kΩ but can range from 800Ω to 3KΩ.

2. For a fixed value of $V_{BI}, I_B \downarrow as V_{CE}$. A lager value of $V_{CE}$ results in a large reverse bias at C-B junction. This $\uparrow$ the depletion region and reduces the effective width of the base. Hence there are fewer recombination in base region and reducing $I_B$