Question

The current Ix in the circuit is 1mA then find the voltage across diode D1. The resistance R1 is 1KΩ. Assume the reverse saturation current is 10^-9A. Voltage across resistor in this condition was 0.4V. Take VT of diode as 0.026V.

(a) 2.3mA

(b) 3.2mA

(c) 5.2mA

(d) 4.6mA

I got this question in examination.

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

Answer 1

Correct option is (c) 5.2mA

The explanation is: Since voltage drop across diode is 0.4V current through resistor is 0.4/1k = 0.4mA

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^-9 x (e^0.4/0.026) = 4.8mA

Total current = 4.8mA+0.4mA = 5.2mA.