Analog Circuits Questions and Answers – Piecewise Linear Model of Diode-2

This set of Analog Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Piecewise Linear Model of Diode-2”.

1. In the given circuit input voltage Vin is 3V and VB is 1.5V. The resistance R is 1.5K. Cut-in voltage of diode is 0.5V. Forward bias resistance is 10Ω. The Voltage V will be ____________
Find the Voltage V input voltage Vin is 3V, VB is 1.5V & Cut-in voltage is 0.5V
a) 2.7V
b) 3V
c) 0.8V
d) 1.5V
View Answer

Answer: b
Explanation: In piecewise linear model, we can consider diode as a voltage source of 0.5V along with an ideal diode. VIN being applied is 3V, which is greater than 1.5-0.5 V, and hence the diode is reverse biased and input appears at output.

2. 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. The voltage V is __________
Find the voltage V if voltage Vin is 3V, VB is 2V, resistor R is 1K Cut-in voltage is 0.7V
a) 0.3V
b) 1V
c) 3V
d) 0V
View Answer

Answer: d
Explanation: In piecewise linear model, we can consider diode as a voltage source of 0.7V along with an ideal diode. VIN being applied is 3V, which is greater than 2-0.7 V, and hence the diode is reverse biased and considering it open, no output is obtained.

3. 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 __________
Find voltage V if Vin is -3V, VB is -2V & Forward bias resistance is 10Ω in circuit
a) -0.29V
b) -4.25V
c) 4.25V
d) 2.9V
View Answer

Answer: b
Explanation: 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.
Equivalent circuit when effective voltage across forward bias mode diode is 1 volt
advertisement
advertisement

4. In the circuit shown below current I is 2mA and VB is 1V. The resistor R is 1K. Cut-in voltage of diode is 0.7V. Forward bias resistance is 10Ω. The voltage V is __________
Find the voltage V if I is 2mA, VB is 1V, resistor R is 1K & Cut-in voltage is 0.7V
a) 3V
b) 2V
c) 1V
d) 0.3V
View Answer

Answer: a
Explanation: Since current source is reverse bias to the diode current passes through resistor R. Voltage across resistor R is 2mA x 1k = 2V. Since resistor and diodes are parallel net output voltage V is VB + voltage across resistor R = 1+2 = 3V.

5. In the circuit shown below current I is 2mA and VB is -1V. The resistor R is 1K. Cut-in voltage of diode is 0.7V. Forward bias resistance is 10Ω. The voltage V is __________
Find voltage V if I is 2mA & VB is -1V, resistor R is 1K & Cut-in voltage is 0.7V
a) 1.3V
b) 0.3V
c) 1V
d) 2V
View Answer

Answer: c
Explanation: Since current source is reverse bias to the diode current passes through resistor R. Voltage across resistor R is 2mA x 1k = 2V. Since resistor and diodes are parallel net output voltage V is VB + voltage across resistor R = -1+2 = 1V.
Sanfoundry Certification Contest of the Month is Live. 100+ Subjects. Participate Now!

6. 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 __________
Find voltage Vout if Vin is 3V, VB is 1V & resistor R1, R2 are 1K in identical diode
a) 1.235V
b) 0.234V
c) 1.314V
d) 1.564V
View Answer

Answer: c
Explanation: Since D1 and D2 are forward biased we can replace them with their equivalent diagram.
D1 & D2 are forward biased hence replaced with their equivalent diagram
Assume I be the current through the circuit. By kirchoff’s voltage rule,
Vout = -VD+IRD+IR2 ————(1)
Current through R1 (Vin-Vout)/1k = (3-Vout)/1k
Current through diode is (Vin-Vout-VD-VB)/RD = (0.3-Vout)/10
Total current I = (3-Vout)/1000+(1.3-Vout)/10 = 1.330-1.010Vout
Substitute this in eq(1)
That is, Vout = -0.7 + 1010(1.33-1.01Vout)
1021Vout = 1342. Therefore, Vout = 1.314V.

7. 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 __________
Find voltage Vin is -3V, VB is -1V, Forward bias resistance is 10Ω & Cut-in voltage 0.7V
a) -2V
b) -3V
c) -1V
d) -.0.7V
View Answer

Answer: b
Explanation: Since both diodes are in reverse bias mode applied voltage Vin will appear on Vout. Diode D1 and D2 disappears and leaves the terminal as open.
advertisement

8. 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 __________
Find voltage Vout if Vin is 3V, VB is 1V & Cut-in voltage of diode is 0.7V in circuit
a) 1.14V
b) 1.23V
c) 0.32V
d) 1.34V
View Answer

Answer: a
Explanation:
Current passing through diode in reverse biased mode D2 by kirchoff’s voltage rule
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.

9. In the circuit shown below voltage Vin is 3V and VB1 is -1V and VB2 is 1V. Assume both diodes are identical. Cut-in voltage of diode is 0.7V. Forward bias resistance is 10Ω. The voltage Vout is __________
Find the voltage Vout Vin is 3V, VB1 is -1V, VB2 is 1V & Forward bias resistance is 10Ω
a) 0.6V
b) 1V
c) 1.7V
d) 2V
View Answer

Answer: a
Explanation: In this condition both diodes are forward biased
Forward biased diode in circuit
This circuit can be further reduced to by assuming VB as 1V
Circuit reduced by assuming VB as 1V by network analysis using kirchoff’s voltage rule
By network analysis using kirchoff’s voltage rule current through RD2 will be 0.09A.
The voltage in Vout will be VB+VD-0.09×10 = 0.6V.
advertisement

10. In the circuit shown below, cut-in voltage of diode is 0.7V. Forward bias resistance is 10Ω. The voltage V is?
Find the voltage V if cut-in voltage of diode is 0.7V & Forward bias resistance is 10Ω
a) 0.69V
b) 0.7V
c) 0.68V
d) 0.72V
View Answer

Answer: d
Explanation: Since diode is in forward bias we can replace diode with voltage source of 0.7V and resistor of resistance 10Ω.
Forward biased diode replaced with voltage source of 0.7V & resistor of resistance 10Ω
Vout will be IRD+VD = 2mAx10 + 0.7 = 0.72V.

Sanfoundry Global Education & Learning Series – Analog Circuits.

To practice all areas of Analog Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

advertisement
advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

Subscribe to his free Masterclasses at Youtube & discussions at Telegram SanfoundryClasses.