Question

What will be the current I in the circuit diagram below. Take terminal voltage of diode as 0.7V and I0as 10^-12A.

(a) 2.4mA

(b) 0.9mA

(c) 1mA

(d) 4mA

This question was addressed to me by my college director while I was bunking the class.

Origin of the question is Characteristic Equation of Diode-1 in portion Diode Circuit of Analog Circuits

Answer 1

Correct choice is (a) 2.4mA

The best explanation: Let VD be the voltage of diode, then by Kirchoff’s loop rule

3V = VD + IR1

This method of assumption contains small error but it is the simplest method.

Let VD be 0.7V. Now the current I = (3-0.7)/1k = 2.3mA. Now the diode voltage for 2.3mA

VD = VT ln⁡(I/I^0) = 0.026 x ln((2.3×10^(-3))/10^(-12)) = 0.5864V.

Now the current becomes (3-0.5864)/1000 = 2.41mA.