Question

In the circuit of $CE$ amplifier, a silicon transistor is used. The value of $V_{CC}=+20V,R_L=3k\Omega$, collector voltage $=5V,\beta =100$. Then the base resistance $R_B$ should be _________$\times 10^5\Omega$. (Take input voltage drop across Si transistor = $0.7V$ )

Answer 1

Answer: 3.86

$V_{CC}=V_C+I_C{R}_L$
$\therefore 20=5+3\times 10^3{I}_C$
$\therefore I_C=\frac{15}{3\times 10^3}$
$=5\times 10^{-3}A=5mA,$
$\beta =\frac{I_C}{I_B}$
$\therefore I_B=\frac{I_C}{\beta }=\frac{5\times 10^{-3}}{100}$
$=5\times 10^{-5}A$
$V_{CC}=I_B{R}_B+$ P.D. across input junction
As silicon transistor is in forward bias,
the P.D. across input junction is $0.7$ volt.
$\therefore 20=5\times 10^{-5}{R}_B+0.7$
$\therefore R_B=\frac{19.3}{5\times 10^{-5}}$
$\therefore R_B=3.86\times 10^5\Omega$
As silicon transistor is in forward bias, the P.D. across input junction is $0.7$ volt.
$\therefore 20=5\times 10^{-5}{R}_B+0.7$
$\therefore R_B=\frac{19.3}{5\times 10^{-5}}$
$\therefore R_B=3.86\times 10^5\Omega$