Question

For the given circuit, if current amplification factor $\beta =90$ and $V_{BE}=0.7V$

Then, base resistance $R_B$ is

• A. $180k\Omega$
• B. $185k\Omega$
• C. $82k\Omega$
• D. $190k\Omega$

Answer 1

Answer: (C)

From Kirchhoff's loop rule in output loop,
$9-4=I_C{R}_C$
As, $R_C=2k\Omega ,$
$\Rightarrow I_C=\frac{5}{2\times 10^3}=2.5mA$
$\Rightarrow I_B=\frac{I_C}{\beta }=\frac{2.5}{90}=27.8\mu A$
$V_{BE}=0.7V$
From Kirchhoff, loop rule in input loop,
$I_B{R}_B=3-0.7$
$\Rightarrow R_B=\frac{2.3}{27.8}\times 10^6=82k\Omega$