Switching Regulator MCQ [Free PDF] – Objective Question Answer for Switching Regulator Quiz

11. Which are the most commonly used low voltage switching regulators?

A. Powdered Permalloy toroids
B. Fermite EI, U and toroid cores
C. Silicon steel EI butt stacks
D. None of the mentioned

The silicon steel EI butt stack exhibits high permeability high flux density and ease of construction and mounting therefore, it is most commonly used in low voltage switching regulators.

12. Find the value of Rsc, L, and Co for a µA7840 switching regulator to provide +5 v at 3A, using the following specifications: toff= 24µs, ripple voltage = 400mA, and ton=26µs.

A. Rsc = 55 mΩ , L = 25µH & Co = 750µF
B. Rsc = 550 mΩ , L = 25µH & Co = 75µF
C. Rsc = 650 mΩ , L = 25µH & Co = 65µF
D. Rsc = 720 mΩ , L = 25µH & Co = 250µF

Peak current

Ipk= 400mA× 1.5 (since Ipk = 1.5 A for peak current)

∴ Rsc = 0.33ohm/Ipk

= 0.33ohm/6 = 0.055ohm.

=> L= [(Vo +Vp) / I pk]×toff

=[(5+1.25) /6 ]× 24×10-6 =25µH.

=> Co = [Ipk (Ton +Toff)]/[8×Vripple]

∵T = [ton + toff] = 26µs + 24µs = 50µs

=> Co = [ (6×50µs)]/(8×50mA. = 7.5×10-4 = 750µF.

13. Calculate the efficiency of the step-down switching regulator has given the input voltage Vin= 13.5v and output voltage =6v. Assume the saturating Voltage Vs=1.1v and the forward voltage drop Vd = 1.257v

A. η = 75%
B. η = 48.5%
C. η = 63.9%
D. η = 80.5%

Efficiency of the step down switching regulator

η = {[(Vin-Vs+Vd)]/ [Vin]}×(Vo) / [(Vo+Vd)]

= {[(13.5v-1.1v+1.257v)/13.5v]} ×[(6/(6 ×1.257)]

=> Efficiency of switching regulator, η = (1.012×0.7955)×100 =

0.8051×100 = 80.5%.

14. Match the characteristics of various switching regulators.

 Switching regulator Characteristics 1. Inverting (i) [ton / toff ] = [ Vo + Vd] / [Vin -Vs -Vd]; Rsc = ( 0.33/ Ipk) 2. step down (ii) [ton / toff ] = [ Vo + Vd -Vin] / [Vin-Vs] ; Rsc = ( 0.33/ Ipk) 3. step up (iii) [ton / toff ] = [ Modulus Vo +Vd] / (Vin-Vs); Rsc = ( 0.33/ Ipk

A. 1- iii , 2- i , 3- ii
B. 1- i , 2- ii , 3- iii
C. 1- iii , 2- ii , 3- i
D. 1- iii , 2- ii , 3- i

Characteristics and design formula for step up, step down and converting mode of switching regulator.

15. What is the conversion ratio of the phase detector in 565 PLL?

A. 0.14
B. 0.35
C. 0.4458
D. 0.7

The conversion ratio of the phase detector of

565 PLL (Monolithic PLL) Kφ = 1.4/π = 0.4458.

16. Given fo = 1.2kHz and V = 13v, find the lock-in range of the monolithic Phase-Locked Loop.

A. ±575Hz
B. ±720Hz
C. ±150Hz
D. ±1kHz

The lock-in range of monolithic PLL,

△fL = ±(7.8×fo)/V = ±(7.8×1.2kHz)/13 = ±720Hz.

17.  A monolithic phase detector is preferred for critical applications as it is:

A. Independent of variation in amplitude
B. Independent of variation in the duty cycle of the input waveform
C. Independent of variation in response time
D. Both 1 and 2

Monolithic phase detectors are not sensitive to harmonics of the input signal and changes in the duty cycle of input and output frequency.

18. Determine the capture range of IC PLL 565 for a lock-in range of ± 1kHz.

A. △FC = ±31.453Hz
B. △fc = ±66.505Hz
C. △fc = ±87.653Hz
D. None of the mentioned

The capture range is

△fc = ±[△fL/ (2π×3.6×103×C]0.5

= ±[1kHz/(2π×3.6×kΩ×10µF)]0.5

= ±[1kHz/226.08×-6]0.5 = [4423]0.5 = ±66.505Hz.

19. Find the lock-in range of the monolithic Phase-Locked Loop from the given diagram.

A. -fo-△fL to fo-△fL
B. -fo-△fL to -fo-△fC
C. fo-△fL to fo-△fC
D. -fo-△fC to fo-△fC

Lock-in range of monolithic PLL is from -fo-△fL to fo-△fL.

20. At what range the PLL can maintain the lock in the circuit?

A. Lock in range
B. Input range
C. Feedback loop range
D. None of the mentioned

The change in frequency of the incoming signal can be tracked when the PLL is locked. So, the range of frequencies over which PLL maintains the lock with the incoming signal is called the lock-in range.

21. At which state the phase-locked loop tracks any change in input frequency?

A. Free running state
B. Capture state
C. Phase-locked state
D. All of the mentioned