Question

If resistance R1 is 10K, V2 = -2V, V1 = -3V then the current I through the circuit will be ___________ (Use constant voltage drop model of diode and take VD as 0.5V)

(a) 0.5mA

(b) 0.25mA

(c) 2mA

(d) 3mA

This question was addressed to me in quiz.

My question is taken from Constant Voltage Drop Model-1 in chapter Diode Circuit of Analog Circuits

Answer 1

The correct answer is (b) 0.25mA

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 both voltage sources are forward biased the diode V2 and diode can be replaced by a single cell of VD. So net voltage in the circuit is 2.5V. So the current will be 0.25mA.