250+ TOP MCQs on Voltage Regulators – 1 and Answers

Analog Circuits Multiple Choice Questions on “Voltage Regulators – 1”.

1. What is IC 723?
A. A voltage regulator
B. A full-wave rectifier
C. A half-wave rectifier
D. A clipper

Answer: A
Clarification: The IC 723 is a voltage regulator, which can act as both a low voltage regulator as well as a high voltage regulator. Output can be set between 7-37 volts. 7 volts is the reference starting voltage.

2. Consider the circuit shown below where the breakdown voltage of the diode is 5V. Source voltage varies between 6V to 12V.

Find the maximum current through the R2, given that R1=2kΩ and R2=5kΩ.
A. 3.5 mA
B. 1 mA
C. 1.4mA
D. 0.2 mA

Answer: C
Clarification: Source current is I = V_S-V_Z/R₂
Thus here I is maximum when V_S is maximum.
I = 12-5/5000 = 1.4 mA.

3. For a Zener diode shunt regulator, the source current is I_S, the Zener diode current is I_Z and the load current is I_L. The source voltage is V_S, Zener voltage is V_Z and load voltage is V_L. The load resistance is R_L. What is the correct option for the safe operation of the diode?
A. I_S = I_Z + I_L
B. I_S =< I_Zmax + I_L
C. I_S =< I_Zmin + I_L
D. V_L = V_Z

Answer: B
Clarification: For proper operation, the current through RS should be at least equal to the sum of I_Zmin a specified load current. I_S >= IZ_min + I_L
For safe operation of the diode, I_S =< I_Zmax + I_L.

4. What is line regulation?
A. The process of keeping Zener diode voltage constant inspite of changes in AC supply
B. The process of keeping load voltage constant irrespective of the fluctuation in AC supply or the line voltage
C. The process of keeping load voltage constant irrespective of fluctuation in load current
D. The process of keeping Zener current constant irrespective of fluctuation in AC supply

Answer: b
Clarification: Line regulation is the process of keeping the load voltage constant, irrespective of fluctuation in AC supply or the line voltage. In line regulation, the load current is considered constant.

5. What is load regulation?
A. The process of keeping the load voltage constant irrespective of any change in AC supply
B. The process of keeping the load voltage constant irrespective of variations in load current
C. The process of keeping load voltage constant irrespective of variations in source current
D. The process of keeping load current constant irrespective of variations in AC supply

Answer: B
Clarification: Load regulation is the process of keeping V_O constant irrespective of variations in load current. The line voltage is taken to be constant during load regulation.

6. Find the power rating of the diode in the given circuit. The breakdown voltage of the diode is 5V.

A. 200 mW
B. 125 mW
C. 250 mW
D. 300 mW

Answer: C
Clarification: Source current I_S = 15-5/200 = 0.05A = 50 mA
The power rating of the diode is the maximum power it can dissipate which occurs when the load is disconnected because then the whole current flows into the diode.
Hence maximum power rating is P = V_ZxI_Z = 5×50 = 250 mW.

7. The following circuit is provided.

Given that V1 varies from 20V to 50V, the diode breakdown voltage is 5V, the knee current is 1mA and the current is 9 mA across R1, find the maximum value of R2.
A. 4500Ω
B. 1500Ω
C. 2000Ω
D. 5000Ω

Answer: B
Clarification: I_S >= I_Zmin + I_L
I_S >= 10mA
V1-5/R2 >= 10mA
R2 =< V1-5/10^-2
Thus R2 =< 1500Ω when V1 = 20V
And R2 =< 4500Ω when V1 = 50V
Hence R2 =< 1500Ω.

8. In the figure below, the voltage V1 ranges from 15 to 35V. The load current is 20mA. The diode knee current is 2 mA, the breakdown voltage is 5V and power rating is 200 mW.

Calculate the range of R2 for the circuit to behave properly as a regulator.
A. 400Ω =< R2 =< 500Ω
B. 450Ω =< R2 =< 500Ω
C. 454Ω =< R2 =< 500Ω
D. 454Ω =< R2 =< 600Ω

Answer: C
Clarification: I_S >= I_L + I_Zmin
I_S >= 22mA
I_Zmax = 200mW/5 = 40 mA.
V1 is minimum, I_S >= I_Zmin + I_L
V1-5/R2 >= 22mA
R2 <= 454 Ω
I_S =< I_Zmax + I_L when V_S is maximum
V1-5/R2 =< 60mA
R2 >= 500 Ω
Hence 454Ω =< R2 =< 500Ω.

9. Which of these is a not drawback of Zener diode shunt regulator?
A. The output voltage is fixed
B. The output voltage can vary with temperature
C. Variation in load current needs to be minimal
D. It is difficult to design

Answer: D
Clarification: The Zener diode shunt regulator is a simple voltage regulator circuit that provides a fixed output voltage. However, due to the presence of the Zener diode, the output is temperature dependent because the breakdown voltage of Zener diode depends on temperature. When load current varies a lot, then Zener current also varies which causes a change in output voltage.