Rectifier Viva Questions and Answers

1. Mention the difference of AC and DC power supply. Give the advantages of both?

The alternating current supply (Ac supply) is sinusoidal function and is a function of time (t). That is as time changes, the value of the AC supply also changes. But the DC supply is always constant for every time (t).That is the value of dc current is constant with irrespective of time. The dc current can be storable but the Ac current cannot be stored. For long distance transfer, AC supply is suitable; the dc supply cannot be used for long distances.

2. Explain in detail about regulation and the need of regulation?

Basically we can say that regulation is the measure of change in the magnitude between the sending and receiving end of a component. The use of a voltage regulator is to keep the power level in a stabilized manner. The main use of voltage regulation is to keep the voltages within the required range of a electrical equipment. In other words, in order to keep an electrical equipment work in its prescribed voltage levels, regulation circuit is used  

3. Explain the process of converting AC to DC?

The process of converting an AC voltage to DC voltage requires 4 steps. First the AC voltage is fed to a step down transformer. The 230V, 50Hz input AC voltage is step down to 10-30 V AC voltage. This reduced voltage passes through a rectifier circuit. The heart of a rectifier circuit is a diode. After the rectifier, the voltage is passed to filter circuit. Capacitor is the base of a filter circuit. Filter is used to remove the unwanted components in the circuit. After the filter circuit, a regulator is used to maintain a constant voltage level.

4. Mention the need of a Linear mode power supply?

To drop the excess voltage in a series dissipative component for regulating the output voltage, a linear regulated power supply is used. The linear power supply should be capable of giving minimum operable DC voltage at rated current. The power supply should be capable of over voltage protection, short circuit protection, reduce the ripples and should be independent of changes in temperature.

5. Discuss in detail about transformer and its types?

To increase or decrease the given input AC voltage, a transformer is used. Transformer works based on the principle of Induction. When two coils are closely placed, the voltage transferring process takes place. Transformer has two coils, primary and secondary coils. When an AC voltage is applied to the primary coil, due to induction, a voltage is induced in the secondary terminal. The two types of transformers are:
Step down transformer – To decrease the input voltage
Step up Transformer – To increase the input voltage.

6. Give the need of rectifier, filter and regulator circuits?

The use of a rectifier circuit is to convert the input AC signal to pulsating DC output signal.
The filter circuit converts the pulsating DC to a fluctuating DC signal.
In order to convert the fluctuating DC signal to the exact DC, regulator circuit is used.

7. Discuss in detail about different types of rectifiers and its features?
 
Half Wave Rectifier
There are mainly 3 different types of rectifiers namely: Half wave, full wave and Bridge rectifiers. Out of these three, Bridge rectifier is the best one among these because Bridge rectifier has more efficiency, less ripple factor, more TUF, less peak factor, less PIV and less transformer cost.

8. Define the following terms: ripple factor, efficiency, transformer utilization factor, form factor, peak factor?

The ripple factor can be defined as:

Ripple factor= RMS value of ac component/Average value

The efficiency of a transformer can be defined as:

Efficiency= dc output power / ac input power

The transformer utilization factor (TUF) can be defined as:

TUF= dc power delivered to load/ac rating of transformer secondary

The form factor can be calculated by:

Form factor = RMS value/ average value

The peak factor can be calculated as:

Peak factor= peak value/ rms value

9. Discuss the following terms: average value, RMS value, mention the significance of each?

Average value can be defined as the sum per count, i.e the mean. It can be also defined as the area of one cycle per time period.
Root Mean Square (RMS) value is defined as the Root of Mean (average) of squares.
If the data contains both the positive and negative values, it is difficult to find the average value. Here RMS value is used for identifying the data.

10. Compare all types of rectifiers?

Features
Type of rectifier
Half wave
Full wave
Bridge
Number of Diodes
1
2
4
Max efficiency
40.6%
81.2%
81.2%
Vdc (no load)
Vm
2Vm
2Vm
Average current
Idc
Idc/2
Idc/2
Ripple factor
1.21
0.48
0.48
PIV
Vm
2Vm
Vm
fout
f
2f
2f
TUF
0.287
0.693
0.812
Form factor
1.57
1.11
1.11
Peak factor
2
√2
√2


11. What is the use of ripple factor and regulation in a rectifer.

The fluctuations in signal can be calculated by ripple factor. If the value is less, then the ripples are less. For a DC signal, the ripple factor is Zero.

The variation of DC output voltage as a function of DC load current can be calculated by regulation.

% regulation = [(VNL-VFL)/VFL] x 100% [ideal power supply is 0]

Where, VNL is the no-load voltage and VFL is the full load voltage.


12. Why LC filter is used in FWR circuit?

We know that, in inductor (L) filter, the ripple factor is inversely proportional to load. That is as load increases, the ripple factor decreases. In capacitor (C) filter, the ripple factor is directly proportional to load. That is as load increases, the ripple factor also increases. Thus if we use a LC circuit then in LC filter, the ripple factor will be independent of load.

13. Mention the different filters used in AC to DC converters?

The different filters used in AC to DC converter are:
L, C, LC(L-section), π-section, RC filters.
Out of these filters, L-section is mostly used because its ripple factor is independent of load.

14. Give the comparison of different types of filters?

Features
Type of Filter
None
L
C
L-Section
π-Section
Vdc at no load
0.636 Vm
0.636 Vm
Vm
Vm
Vm
Vdc at load Idc
0.636 Vm
0.636 Vm
Vm - 4170Idc/C
0.636 Vm
Vm - 4170Idc/C
Ripple Factor
0.48
RL/16000 L
2410/CRL
0.83/LC

Peak inverse voltage (PIV)
2 Vm
2 Vm
2 Vm
2 Vm
2 Vm

15. Differentiate between line regulation and load regulation?

The line regulation can be defined as:

Line regulation = change in output voltage/ change in input voltage

The load regulation can be defined as:

Load regulation = (no load voltage- full load voltage)/ no load voltage

16. Explain knee voltage?

Knee voltage can be defined as the minimum amount of voltage which is required to operate a Diode

17. Explain knee current?

Knee current is the minimum current through Zener diode in reverse bias condition.

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