• # question_answer Consider the circuit arrangement as shown in figure for studying input and output characteristics of n-p-n transistor in CE configuration. Select the values of ${{R}_{B}}$ and ${{R}_{C}}$ for a transistor whose ${{V}_{BE}}=0.7V,$ so that the transistor is operating at point Q as shown in the characteristics curve. Given that the input impedance of the transistor is very small and ${{V}_{CC}}={{V}_{BB}}=16V,$ find the voltage gain and power gain of circuit making appropriate assumptions.

 Given, ${{V}_{BE}}=0.7V,$ ${{V}_{CC}}={{V}_{BB}}=16V$ ${{V}_{CE}}=8V$ (from graph) ${{I}_{C}}=4mA=4\times {{10}^{-3}}A$ ${{I}_{B}}=30\mu A=30\times {{10}^{-6}}A$
For the output characteristic at Q ${{V}_{CC}}={{I}_{C}}{{R}_{C}}+{{V}_{CE}}$ ${{R}_{C}}=\frac{{{V}_{CC}}-{{V}_{CE}}}{{{I}_{C}}}=\frac{16-8}{4\times {{10}^{-3}}}$             $=\frac{8000}{4}=2k\Omega$ Using the relation ${{V}_{BB}}={{I}_{B}}{{R}_{B}}+{{V}_{BE}}$ ${{R}_{B}}=\frac{{{V}_{BB}}-{{V}_{BE}}}{{{I}_{B}}}$ $=\frac{16-0.7}{30\times {{10}^{-6}}}=510\times {{10}^{3}}\Omega =510k\Omega$ $\beta =\frac{{{I}_{C}}}{{{I}_{B}}}=\frac{4\times {{10}^{-3}}}{30\times {{10}^{-6}}}\approx 133$ Voltage gain $=\beta \times \frac{{{R}_{C}}}{{{R}_{B}}}=\frac{133\times 2\times {{10}^{3}}}{510\times {{10}^{3}}}=0.52$ Power gain $=\beta \times$Voltage gain $=133\times 0.52=69.36$