Question

In common emitter amplifier, current gain is 80 and emitter current is 9 mA. The base current is​

Answer 1

The base current is (1/9)mA [option D]

Given :

Current gain β = 80

Emitter current  $I_{e}$ = 9mA

To find :

Base current  $I_{b}$ = ?

Solution :

In a common emitter amplifier;

Current gain = Collector current / Base current

                   β = $I_{c} / I_{b}$

                  $I_{c}$ = β$I_{b}$  ⇒ eq.(1)

Emitter current = Collector current + Base current

                   $I_{e} = I_{c} + I_{b}$

From eq.(1) $I_{e}$ =  β$I_{b}$ +  $I_{b}$ = (β + 1)$I_{b}$ = (80+1)$I_{b}$

                      $I_{e}$ =  81 $I_{b}$

Therefore the base current  $I_{b}$ = $I_{e}$ / 81  = (9 mA) / 81

                                               $I_{b}$ = (1/9)mA  

The base current is (1/9)mA