Question

In the circuit shown below voltage Vin is -3V and VB is -2V. The resistor R is 1K. Cut-in voltage of diode is 0.7V. Forward bias resistance is 10Ω. The voltage V is __________

(a) -0.29V

(b) -4.25V

(c) 4.25V

(d) 2.9V

I had been asked this question during an online exam.

I want to ask this question from Piecewise Linear Model of Diode-2 in chapter Diode Circuit of Analog Circuits

Answer 1

The correct choice is (b) -4.25V

For explanation I would say: Effective voltage across diode is one volt. Hence diode is in forward bias mode. So we can apply equivalent circuit of diode.

Net voltage through R and RD is -3-2+0.7 = -4.3V

Current through the circuit is -4.3/(R+RD) = -4.3/(1010) = -0.00425A=-4.25 mA

Hence voltage across R is 1Kx(-4.25mA) = -4.25V.