GATE 2015 EE – SET 1 Question 14

Solution :

$$\frac{R_{B}}{R_{C}} $$ = ?

$$ V_{C}$$= 9V , $$\beta $$= 75
$$V_{BE}$$ = 0.7V

$$I_{C}$$= $$\beta I_{B}$$

$$I_{C} + I_{B}$$  =$$\frac{15-V_{C}}{R_{C}} $$= $$\frac{15-9}{R_{C}}$$ = $$\frac{6}{R_{C}}$$

$$I_{C} + I_{B}$$ =$$ \frac{6}{R_{C}}$$

$$\beta I_{B}$$ + $$\ I_{B}$$ = $$ \frac{6}{R_{C}}$$

$$ \Rightarrow $$ 76 $$I_{B} $$ = $$\frac{6}{R_{C}}$$  ———(1)

 

$$I_{B}$$= $$\frac{9-0.7}{R_{B}}$$ = $$\frac{8.3}{R_{B}}$$
$$\therefore I_{B}$$= $$ \frac{8.3}{R_{B}}$$

$$\therefore$$ 76$$I_{B}$$ =$$ \frac{6}{R_{C}}$$

76 $$\left ( \frac{8.3}{R_{B}} \right )$$ =$$ \frac{6}{R_{C}}$$

$$\frac{R_{B}}{R_{C}}$$= $$\frac{76*8.3}{6}$$ =105.1