Question

What is current I if voltage V = 5V, VB = 2V, R1 & R2 = 2K. (Use constant voltage drop model assumption and take VD = 0.5V)

(a) 1.25mA

(b) 1mA

(c) 2.75mA

(d) 1.75mA

The question was asked in an interview for internship.

My enquiry is from Constant Voltage Drop Model-2 topic in portion Diode Circuit of Analog Circuits

Answer 1

Right option is (c) 2.75mA

For explanation: In constant voltage drop model at forward bias diode can be replaced as a cell and in reverse bias diode can be avoided by considering the terminals are open.

Since Vin and VB are opposite net voltage is 3V. Voltage at R1 is 3V so current is 1.5mA. Voltage at R2 is 3-0.5 = 2.5V. So the current is 1.25mA. The net current is 2.75mA.