# Power Electronics Technical Interview Questions: Set-2

Power Electronics Technical Interview Questions and Answers:

Some of the Power electronics technical interview questions with answers are given in this post. These questions were asked in various power electronics company interviews to some of our friends. We collected the questions from our friends and answer them in detail. We are confident that these Power Electronics Technical Interview Questions will be helpful for you, while preparing for interviews...

[Q-1]  Draw the buck topology?
In most of the power electronics interview questions, you are going to face this basic question. Not only buck converter, the interviewer may ask you to draw other fundamental topologies too...

So you should be familiar with other basic topologies like Flyback, Boost , Buck-boost....

[Q-2]  Which is the good choice among the 2 options mentioned below to get the 12V as an output? why?
Option I: Input voltage = 48V,
Option II: Input voltage = 24V

Duty cycle D = Vout / VInput

For case I
D = 12/48 = 0.25

For case II
D = 12/24 = 0.5

So for case II, the duty cycle is more than case I.
It means device is turned ON more time in the second case. while designing SMPS we have to consider the principle mentioned in Q-3.

[Q-3] What is effect of having more duty cycle and less duty cycle? ( continuation of above question)
If the duty cycle D is greater than 0.5, the core would not be completely demagnetized at the end of the off-period, and a DC magnetization of the core would build up, resulting in core saturation.
Relate this answer the previous question....

[Q-4] To design the buck converter, what are basic & essential information (parameters) we need to get from the Customer?
We need the following inputs from the customer,
Output Voltage VOUT
Input Voltage VIN
Maximum Ripple voltage allowed at the output side
Efficiency of the converter

[Q-5] How to select the inductor for the buck converter?
Once the topology is finalized in the process of power supply design, the next step is selecting the Inductor.
We know the following basic equation
Voltage across Inductor VL = L di/dt
Rewriting the above equation as follows
L = VL.dt/di
VL = Maximum voltage appears across the Inductor
dt= The time during which the maximum voltage appears across the inductor
di = Ripple current
VL The maximum voltage appears across the inductor when the power switch is turned on. During that time the voltage will be
VL = VOUT - VIN
dt = The time during which the maximum voltage appears across the inductor
= D/FS
= Duty cycle/Switching frequency
di = Ripple current
= Generally it is assumed in between 10% to 30% of the load current
By knowing all these values we can get the required inductor value for the buck converter.

[Q-6] What are the various parameters we have to consider, while selecting IGBT?
In IGBT datasheet, we have to focus on following parameters
Collector to emitter voltage VCES
Collector Current IC
Collector Dissipation PC
Junction Temperature Tj

[Q-6] For Selecting MOSFET, what are the major parameters we have to consider in the datasheet?
In MOSFET datasheet, we have to focus on following parameters:

Drain to Source Voltage VDSS
On state Drain to Source Resistance RDS(ON)
Reverse Recovery Current IRR
Reverse Recovery Charge QRR
Gate Charge QG
Body Diode Characteristics

ID at ambient temperature
Channel power dissipation
Channel temperature

We believe that these power electronics technical interview questions might have stimulated your technical knowledge... If you have questions why don't you share with our subscribers?

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### 4 Responses

1. ajaz ahmed k says:

thanks for giving good information

2. sara says:

very useful

3. jagannath says:

Is good