The diode used in the circuit shown in the figure has a constant voltage drop of 0.5 V at all currents and a maximum power rating of 100 mW. What should be the value of the resistance R connected in series with diode for obtaining maximum current?

10 Ω

Voltage drop across diode, $V_d= 0.5V$

Maximum power rating, P = 100 mW

$=100×10^{-3} W =0.1W$

Diode resistance, $R_d=\frac{V_d^2}{P}=\frac{(0.5V)^2}{0.1W}=2.5Ω$

Current in diode, $I_d=\frac{V_d}{R_d}=\frac{0.5V}{2.5Ω}=0.2A$

Total resistance of the circuit = $\frac{2.5V}{0.2A}= 12.5Ω$

Resistance R in circuit, $R = 12.5 W – 2.5 W = 10 W$