Question

A current of 5.4 mA is required through the LED to make it work properly in given circuit. The minimum value of input voltage to be applied to the input to make the LED glow is (Assume $V_{BE}=0.7V$).

• A. 9.61 V
• B. 10 V
• C. 4.80 V
• D. 6.42 V

Answer 1

The correct option is A 9.61 V

For given circuit,


We know, $I_B=\frac{V_{in}-V_{BE}}{R_B}$

Also, $I_B=\frac{I_C}{\beta }$

Putting the values for given circuit in equation,

$\frac{I_C}{\beta }=\frac{V_{in}-V_{BE}}{R_B}$

$\frac{5.4\times {10}^{-3}}{200}=\frac{V_{in}-0.7}{330\times {10}^3}$

$330\times {10}^3\times (2.7\times {10}^{-5})=V_{in}-0.7$

$V_{i}n=9.61V$