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1. In constant voltage drop model diode in forward bias is considered as a
a) Resistor
b) Perfect conductor
c) Perfect insulator
d) capacitor

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Answer: b [Reason:] In constant voltage drop model the diode is considered as a perfect conductor in forward bias and perfect insulator in reverse bias. That is voltage drop at forward bias is zero and current through the diode at reverse bias is zero. In this 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.

2. In constant voltage drop diode in reverse bias is considered as a
a) Resistor
b) Perfect conductor
c) Perfect insulator
d) capacitor

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Answer: c [Reason:] In constant voltage drop the diode is considered as a perfect conductor in forward bias and perfect insulator in reverse bias. That is voltage drop at forward bias is zero and current through the diode at reverse bias is zero. In this 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.

3. The current I through the circuit if we consider diode in constant voltage drop model is
(Take VD as 0.5V)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q3
a) 2mA
b) 2.5mA
c) 3.5mA
d) 1mA

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Answer: b [Reason:] 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 D1 is in forward biased there will be a voltage drop of 0.5V. So net voltage will be 2.5V and hence current is 2.5mA.

4. The voltage across the diode Vout if Vin is -5V and resistance is 10K is
(Use constant voltage drop model of diode and take VD as 0.5V)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q4
a) -3V
b) 0V
c) -5V
d) -2.5V

View Answer

Answer: c [Reason:] 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 diode is reverse biased entire voltage will appear across diode.

5. The voltage across the diode Vout if Vin is 5V and resistance is 10K is
(Use constant voltage drop model of diode and take VD as 0.5V)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q4
a) 5V
b) 0.5V
c) 2.5V
d) 0V

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Answer: b [Reason:] 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 diode is forward biased and potential is greater than VD voltage across diode is VD.

6. The current I through the circuit I if voltage v is -3V is
(Use constant voltage drop model of diode and take VD as 0.5V)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q6
a) 10mA
b) 1mA
c) 3mA
d) 0mA

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Answer: d [Reason:] 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 diode is reverse biased there is no current through the circuit.

7. If current source produces a current of 1mA and resistance R is 3K then voltage across the resistor is
(Use constant voltage drop model of diode and take VD as 0.5V)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q7
a) 3V
b) 0V
c) 0.5V
d) 0.3V

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Answer: c [Reason:] 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 diode is forward biased and maximum voltage if all current pass through resistor Is 3V which is greater than VD voltage across diode is VD.

8. 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)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q8
a) 0.3mA
b) 0.6mA
c) 0.7mA
d) 0.1mA

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Answer: d [Reason:] In ideal diode model the diode is considered as a perfect conductor in forward bias and perfect insulator in reverse bias. That is voltage drop at forward bias is zero and current through the diode at reverse bias is zero. Since both voltage is reverse bias to diode the diode will disappear from the circuit. Then effective voltage becomes 3-2 = 1V so current is 1/10K = 0.1mA.

9. 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)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q8
a) 0.5mA
b) 0.25mA
c) 2mA
d) 3mA

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Answer: b [Reason:] 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.

10. What will be the voltage Vout if VA = 3V and VB = -5V?
(Use constant voltage drop model of diode and take VD as 0.5V)
analog-circuits-questions-answers-constant-voltage-drop-model-1-q10
a) 2.5
b) 3.5
c) -5.5
d) -4.5

View Answer

Answer: a [Reason:] 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 first diode is forward biased and second diode reverse bias, first voltage appears on resistor with a voltage drop of VD.