IC Voltage Regulator MCQ [Free PDF] - Objective Question Answer for IC Voltage Regulator Quiz

11. In the circuit given below, let V_EB(ON)=0.8v and ß=16. Calculate the output current coming from 7805 IC and collector current coming from transistor Q₁ for a load of 5Ω.

A. I_O =111mA, I_C= 808mA
B. I_O =111mA, I_C= 829mA
C. I_O =111mA, I_C= 881mA
D. I_O =111mA, I_C= 889mA

Answer: D

When load = 5Ω, I_L= 5v/5Ω =1A.

The voltage across R₁ is 7Ω × 1A=7v.

Since I_L is more than 100mA, the transistor Q₁ turns on and supplies the extra current required.

Therefore

I_L =(ß+1)I_O-[ß×(V_EB(ON)/R₁)

I_O = [I_L/(ß+1)]+ [ß×(V_EB(ON)/R₁)

= [1/(16+1)]+[16×(0.8/2Ω)] ≅111mA.

=> I_C=I_L-I_O=1A-111mA =889mA.

12. Calculate the output voltage for the LM314 regulator. The current I_ADJ is very small in the order of 100µA. (Assume V_REF=1.25v)

A. 17.17v
B. 34.25v
C. 89.34v
D. 23.12v

Answer: A

The output voltage

V_O =V_REF[1=(R₂/R₁)]+(I_ADJ×R₂)

=1.25V_in× [1+(3kΩ/240Ω)] +( 100µA×3kΩ )

= 16.875 +0.3.

=> V_O=17.17v.

13. Compute the input voltage of the 7805c voltage regulator with a current source that will deliver a 0.725A current to a 65Ω, 10w load. (Assume reference voltage =5v)

A. V_in = 84v
B. V_in = 34v
C. V_in = 54v
D. V_in = 64v

Answer: C

V_O=V_REF+V_L =V_REF+(I_L×R_L)

= 5v+(0.725A×65Ω) = 52.125v

=> Input voltage, V_in = V_O + dropout voltage = 52.125v+2v.

=> V_in ≅54v.

14. Which of the following is not a characteristic of adjustable voltage regulators?

A. Non-versatile
B. Better performance
C. Increased reliability
D. None of the mentioned

Answer: A

Adjustable voltage regulators are versatile; it has improved over-load protection allowing greater output current over an operating temperature range.

15. What is done in switching regulators to minimize their power dissipation during switching?

A. Uses external transistor
B. Uses 1mH choke
C. Uses external transistor and 1mH choke
D. None of the mentioned

Answer: C

To minimize power dissipation during switching, the external transistor must be a switching power transistor and a 1mH choke smooth out the current pulses delivered to the load.

16. Fixed voltage regulators and adjustable regulators are often called as
A. Series dissipative regulators
B. Shunt dissipative regulators
C. Stray dissipative regulators
D. All the mentioned

Answer: A

Series dissipative regulators simulate a variable resistance between the input voltage & the load and hence function in a linear mode.

16. Linear series regulators are suited for application with

A. High current
B. Medium current
C. Low current
D. None of the mentioned

Answer: B

In series dissipative regulators, conversion efficiency decreases as the input or output voltage differential increases and vice versa. So, linear series regulators are suited for medium current applications with a small voltage differential.

17. A series of switching regulators

A. Improves the efficiency of regulators
B. Improves the flexibility of switching
C. Enhance the response of regulators
D. All of the mentioned

Answer: A

A series of switching regulators are constructed such that, a series pass transistor is used as a switch rather than as a variable resistance in linear mode.

18. The switching regulators can operate in

A. Step up
B. Stepdown
C. Polarity inverting
D. All the mentioned

Answer: D

The switching regulators can operate in any one of the three modes depending on how the components are connected.

19. What are the conditions to be satisfied by a voltage source for using it in a switching regulator.

1. It must supply the required output power and the losses associated with the switching regulator

2. It must be large enough to supply sufficient dynamic range line and load variations

3. It must be sufficiently high to meet the minimum requirement of the regulator system to be designed

4. It may be required to store energy for a specified amount of time during power failure especially if the system is designed for a computer power supply.

A. 1 and 3
B. 1,2,3 and 4
C. 2,3 and 4
D. 1,3 and 4

Answer: B

A voltage source must satisfy the entire given requirement to be used in the switching regulator.

20. Which of the following act as a switch in the switching regulator?

A. Rectifiers
B. Diode
C. Transistors
D. Relays

Answer: C

A transistor is connected as a power switch and is operated in the saturated mode. Thus, the pulse generator output alternatively turns the switch ON and OFF in the switching regulator.

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