Power Supply related Interview Questions with Answers -Set10

Power Supply related Interview Questions with Answers

In this post we have shared some of simple interview questions related to power supply.
Before proceeding further it is good to refresh about Power Supply Terminology.

[1] Draw the block diagram of the general power supply?

This is most general interview question related to power supply.
This is starting question and the interviewer will go in depth in each section.

[2] How to provide Over current protection in a power supply?
Using Fuse we can protect the power supply against over current.
We have to insert the fuse in the phase line.

[3] How to protect power supply against applying reverse voltage?
By including diode in the phase line we can protect the circuit against applying reverse voltage.
If we use schottky diode we can reduce power dissipation across the diode as the power dissipation = Vf x I

[4 ] Why schottky diodes are used in reverse voltage protection section? Why the rectifier diodes are not used in those places?
For the same load current, the forward voltage drop Vf is less in schottky diode compare to normal rectifier grade diodes.
It gives low power loss. [Power dissipation = Vf x I]

[5 ] What are the advantages of schottky diode?

• They are having low forward voltage drop (Vf).
So the power dissipation is less compared to that of rectifier diodes.
• They are having low reverse recovery time (Trr).
So they can be truned ON/OFF at very speed. ie, They are having high switching speed.
So they are used in high frequency applications like SMPS.

[6] How to protect the power supply against over voltages or surge voltages?
By using MOV (Metal Oxide Varistor) we can suppress the surge voltages.
The MOV is connected across the phase and neutral lines.

[7 ] What is load regulation and line regulation?
Line Regulation:
The line regulation is defined as the change in output voltage for a change in line supply voltage keeping the load current and temperature constant.
ie, Line Regulation = Change in Output Voltage / Change in Input Voltage
= ΔVO / ΔVIN

The load Regulation is expressed as follows
Here

These are very fundamental questions related to power supply topic.

2 Responses

1. Abhishek says:

Effort appreciated
Well done...we look fwd for more and willing to contribute as well

2. Sam Ochi says:

How about the use of synchronous rectifiers (in 1 under Rectifier) for reducing power dissipation during rectification of the AC to DC? It is well known that a bridge rectifier will drop ~4* 0.6V=2.4V (for Schottky diodes..) or ~4*1V (for standard PN silicon diodes.). This loss is very significant if one wants to build >90% efficient power supplies off AC.
Also, regarding overcurrent protection, in (2), have one used a current limiting device? This current limiting device will instantly limit, say 20A or so and keep it at 20A. Once the overcurrent condition drops below 20A -- say 19A, the device will drop out. This device, if designed properly can limit within ns of the overcurrent event, unlike a fuse. It also resets automatically as soon as the overcurrent condition is gone.