## Rectifiers Interview Questions and Answers:

1. What is a dc power supply?

Ans. The part of the equipment that converts ac into dc is called the dc power supply.

2. What is meant by rectifier?

Ans. A rectifier is a device which converts alternating current (or voltage) into unidirectional current (or voltage).

3. Enumerate the properties that the junction diodes designed for use as rectifiers should possess.

Ans. Junction diodes designed for use in rectifiers should have the properties : (i) V-I characteristics as close as possible to that of an ideal diode (ii) Negligible forward resistance (iii) Negligible reverse current i.e., large reverse resistance (iv) Large reverse breakdown voltage and (v) Small offset voltage V0 in the forward direction.

4. Define peak inverse voltage (PIV) of a diode. What is the difference between PIV of a center tapped FWR and bridge rectifier?

Ans. Peak inverse voltage (PIV) is the maximum possible voltage that occurs across a diode when it is reverse biased. PIV of a center-tapped FWR is double of that of bridge rectifier.

5. What is the importance of peak inverse voltage?

Ans. If the applied voltage in reverse biased condition exceeds peak inverse voltage (PIV) rating of the diode, then the diode may get damaged.

6. What are the PIVs for full-wave center-tapped transformer and bridge rectifier respectively?

Ans. Peak inverse voltage of center-tapped transformer full-wave rectifier = 2VSmax, where VSmax represents the maximum voltage across each half of the secondary winding.

Peak-inverse voltage of bridge rectifier = VSmax, where VSmax is the maximum voltage across the transformer secondary.

7. What is PIV for half-wave and full-wave center-tapped transformer rectifier?

Ans. Peak inverse voltage (PIV) of half-wave rectifier is Vmax, where VSmax is maximum voltage of transformer secondary.

Peak inverse voltage of center-tapped transformer full-wave rectifier = 2 VSmax, where VSmax represents the maximum voltage across each half of the secondary winding.

8. Why half-wave rectifiers are generally not used in dc power supply?

Ans. The type of supply available from half-wave rectifier is not satisfactory for general power supply. That is why it is generally not used in dc power supply.

9. Why diodes are not operated in the breakdown region in rectifiers?

Ans. In breakdown region. a diode has a risk of getting damaged or burnt because the magnitude of current flowing through it increases in an uncontrollable manner. That is why diodes are not operated in the breakdown region in rectifiers.

10. What is ripple factor?

Ans. The pulsating output of a rectifier can be considered to contain a dc component and ac components called the ripples. The ripple current is undesirable and its value should be the smallest possible in order to make the rectifier effective.

The ripple voltage or current is measured in terms of the ripple factor which is defined as the ratio of the effective value of the ac components of voltage (or current) present in the output from the rectifier to the direct or average value of the output voltage (or current).

11. What is ripple factor for full-wave rectifier?

Ans. Ripple factor for full-wave rectifier is 0.482.

12. What is transformer utilization factor?

Ans. Transformer utilization factor is defined as the ratio of power delivered to the load and ac rating of secondary of supply power transformer.

13. The output of a 60 Hz full-wave bridge rectifier has a 60 Hz ripple. Is the circuit working properly?

Ans. A full-wave rectifier with 60 Hz input must have lowest ripple frequency equal to twice the input frequency i.e., 120 Hz. If the ripple frequency is 60 Hz, it means some diodes in the circuit are not working.

14. What is meant by filter?

Ans. Filter is a device that converts pulsating output of rectifier into a steady dc level.

15. Explain why a capacitor and an inductor can act as filtering components?

Ans. The filtering action of L and C depends upon the facts that an inductor allows dc only and capacitor allow ac only to pass i.e. the filtering action of an inductor filter depends upon its property of opposing any change in current flowing through it where as the action of capacitor filter depends upon its property of opposing any change in the voltage applied across its ends.

16. Why series inductor and L-section filters cannot be used with half-wave rectifiers?

Ans. Series inductor and L-section filters cannot be used with half-wave rectifiers because operation of series inductor depends upon the current through it and needs a minimum current to flow at all times.

17. Why capacitor input filter is preferred to choke input filter?

Ans. In capacitor input filter, the dc output is much larger and ripples are less in comparison to those in choke input filter. So capacitor input filter is preferred to choke input filter.

18. Why π-filters are not suitable for varying loads?

Ans. Voltage regulation in case of π-filters is very poor and, therefore, π-filters are not suitable for varying loads.

19. Why R-C filters are suitable only for light loads?

Ans. R-C filters have poor voltage regulation and need adequate ventilation to dissipate the heat developed in the resistor R. Thus R-C filters are suitable only for light loads.

20. Why is bleeder resistance employed in a filter circuit?

Ans. A resistance, called the bleeder resistance, is placed across the filter output, as shown is Fig. 9.25, to provide flow of necessary minimum current through the choke at all times.

21. What is the purpose of bleeder resistance in a rectifier circuit using L-C filter?

Ans. Bleeder resistance RB is placed in parallel with the load so as to maintain a certain minimum current through the choke, even the load resistor gets open circuited, and improves filtering action.

22. What is meant by voltage regulation of a dc power supply?

Ans. The change in voltage from no-load to full-load condition is known as voltage regulation.

23. Why is it necessary to include voltage stabilizer in a power supply?

Ans. The magnitude of output dc voltage may vary with the variation of either the input ac voltage or the magnitude of load current. So at the output of a rectifier-filter combination (a voltage stabilizer) is required.

24. What is the drawback of a full-wave voltage doubler?

Ans. The drawback of a full-wave voltage doubler is that a common ground between input and output is not available.

25. What is voltage multiplier?

Ans. Voltage multiplier is a modified capacitor filter circuit that delivers a dc voltage twice or more times of the peak value (amplitude) of the input ac voltage.

Scroll to Top