Question

The $$6V$$ Zener diode is shown in figure has negligible resistance and a knee current of $$5mA$$. The minimum value of $$R(in\,\Omega )$$ so that the voltage across it does not fall below $$6V$$ is

Answer 1

Correct option is D. $$80$$
Given

$$V_z = 6 V$$

$$V_{max} = 10 V$$

In zener diode

$$I_s = I_{knee} + I_R$$

where $$I_s = $$ supply current by $$10 V$$

$$= \dfrac{V_{max} - V_z}{R}$$

$$I_R = \dfrac{V_{max} - V_z}{R} - I_{knee}$$

$$= \dfrac{10 - 6}{50} - \dfrac{5}{1000} = \dfrac{75}{1000} A$$.

$$R = \dfrac{V_z}{I_R} = \dfrac{6}{\dfrac{75}{1000}} = \dfrac{6 \times 1000}{75} = 80 \Omega$$