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In the circuit shown below voltage Vin is 3V and VB is 1V. The resistor R1 and R2 are 1K. Assume both diodes are identical. Forward bias resistance is 10Ω. Cut-in voltage of diode is 0.7V. The voltage Vout is __________(a) 1.14V(b) 1.23V(c) 0.32V(d) 1.34VI got this question in an online interview.The question is from Piecewise Linear Model of Diode-2 in portion Diode Circuit of Analog Circuits

Answer»

Correct answer is (a) 1.14V

Explanation: Assume I be the CURRENT through the circuit. By kirchoff’s VOLTAGE rule,

Vout = IR2————(1)

Current through R1 (Vin-Vout-VD)/1.01k = (2.3-Vout)/1010

Current through diode D2 is 0 SINCE D2 is in reverse BIAS mode.

current I = (2.3-Vout)/1010

Substitute this in EQ(1)

That is, Vout = (2.3-Vout)/1010 x 1000=> 1.99Vout = 2.27=> Vout = 2.27/1.99 = 1.144V.


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