Question

Find the current Ix if the voltage across the diode is 0.5V. The reverse saturation current of diode 10^-11A, the cut-in voltage of diode is 0.6V. Assume that the temperature at which diode operates is 25°C. The resistance R1=2KΩ.

(a) 3.97mA

(b) 4.51mA

(c) 2.45mA

(d) 3.05mA

I had been asked this question in an internship interview.

I'd like to ask this question from Characteristic Equation of Diode-2 in division Diode Circuit of Analog Circuits

Answer 1

Correct option is (d) 3.05mA

For explanation: Since voltage drop across diode is 0.5V current through resistor is 0.5/2k = 0.25mA

Current through diode

where I0 = reverse saturation current

             η = ideality factor

             VT = thermal voltage

             V = applied voltage

Since ideality factor is not given take it as one.

Current through diode I = 10^-11 x (e^0.5/0.0257) = 2.8mA

Total current = 2.8mA + 0.25mA = 3.05mA.