This set of Analog Circuits Questions and Answers for Experienced people focuses on “Constant Voltage Drop Model-2”.

1. Voltage across the resistor R if V_{A} = -3V and V_{B} = -5V is _________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 0V

b) -3V

c) -5V

d) -4V

View Answer

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. In above circuit both the diodes are reverse biased and can be considered as open circuit. Hence output voltage is 0V.

2. Current I if voltage V = 5V, V_{B} = 2V, R_{1} & R_{2} = 2K.

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 1.25mA

b) 1mA

c) 2.75mA

d) 1.75mA

View Answer

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 V

_{in}and V

_{B}are opposite net voltage is 3V. Voltage at R

_{1}is 3V so current is 1.5mA. Voltage at R

_{2}is 3-0.5 = 2.5V. So the current is 1.25mA. The net current is 2.75mA.

3. Current I if V = 5V and -5V when V_{B} = 2V, R_{1} = 2K, R_{2} = 4K respectively are __________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 1.3mA, 0.23mA

b) 2.875mA, 0mA

c) 2mA, 0mA

d) 1.423mA, 0 mA

View Answer

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.

When V=5V, diode is in forward bias and net total voltage becomes 4.5V across R1.

Current through branch 1 will be 4.5V / 2K = 2.25mA.

Current through branch 2 will be (4.5-2)/4K = 0.625mA.

So net current is sum of these two. Therefore, net current is 2.875mA.

When V= -5V, the diode is reverse biased and net current flowing is zero.

4. The output voltage V if V_{in} = 3V, R=5K, V_{B} = 2V is ___________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 0V

b) 2V

c) 1.5V

d) 3.5V

View Answer

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 V

_{in}is reverse bias to the diode all voltage will appear across diode and no current flows. Thus, voltage across diode is V

_{in}-V

_{B}= 1V. Net voltage V=3V.

5. In the circuit below V_{B} = 2V, V_{in} = 5V. The voltage V across resistor R is ________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 0V

b) 2.5V

c) 1.5V

d) 3V

View Answer

Explanation: The diode is in reverse bias and voltage across diode is -3V. Hence the voltage across the resistor is V

_{in}+V

_{D}-V

_{B}=5-3-2=0V.

6. In the circuit V_{in} = 4V, V_{B} = 3V, R = 5K. The voltage across diode V is _________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 0V

b) 0.5V

c) 1V

d) 1.5V

View Answer

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. The diode here is in reverse bias and may be considered as an open circuit. Hence, the voltage across the diode is 4-3=1V.

7. In the circuit below V_{in} = 4V, R = 2K and V_{B} = 2V. In these conditions the voltage across diode V is _________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 2.5

b) 4.5

c) 0.5

d) 1.5

View Answer

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 diode is forward biased it will produce a voltage drop of V

_{D}.

8. In the circuit shown in below I = 2mA, V_{B} = 2V and R = 2K. The voltage V will be ________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 0V

b) 2.5V

c) 6V

d) 3.5V

View Answer

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 current source forward bases the diode voltage drop across diode is V

_{D}. So net voltage output is V

_{D}+V

_{B}.

9. In the circuit shown in below I = 2mA, V_{B} = 2V and R = 2K. The voltage V will be ________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 4V

b) 3V

c) 6V

d) 5.5V

View Answer

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 current source reverse biases diode, all current pass through resistor R. So voltage across resistor is 4V. Since voltage source cannot produce current due to lack of closed circuit total voltage at the output is 6V.

10. For circuit shown below V_{in} = 3V, R_{1} = 6K, R_{2} = 2K. The voltage V will be ________

(Use constant voltage drop model assumption and take V_{D} = 0.5V)

a) 2V

b) 3V

c) 3.5V

d) 2.5V

View Answer

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 diode is forward biased and parallel to resistor R

_{1}voltage drop across diode is V

_{D}. So net voltage equals to V

_{in}–V

_{D}.

**Sanfoundry Global Education & Learning Series – Analog Circuits.**

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