Question

Find voltage VOUT if the reverse saturation current of the diode is  1.1×10^-8A, the cut-in voltage of diode is 0.6V and assume the temperature as 25^oC.

(a) 0.235V

(b) 0.3148V

(c) 0.456V

(d) 0.126V

This question was addressed to me in an interview for job.

My question is from Characteristic Equation of Diode-2 topic in division Diode Circuit of Analog Circuits

Answer 1

Correct answer is (b) 0.3148V

The explanation: Equation for diode current

                            where I0 = reverse saturation current

             η = ideality factor

             VT = thermal voltage

             V = applied voltage

Since in this question ideality factor is not mentioned it can be taken as one. Take VT as its standard value 0.026V.

Voltage VD = ηVTln(I/IO + 1) = 1 x 0.0257ln (2 x 10^-3/(1.1 x 10^-9))+1) = 0.0257ln(1,818,182) = 0.3704 V.