Basic Power Electronics Interview Questions and Answers ( sai saikumar jn)

 Power Electronics Interview Questions: Set-1

Basic Power Electronics Interview Questions

This post consists of some of the frequently asked Power Electronics interview questions Considering that the Candidate is Fresher and has no hands on experience with him. But these basic power electronics interview questions will be useful for others too to refresh their basics…

   

[Q-1] What is holding current in SCR?
It is the minimum current required to hold the SCR in forward conduction state.
When the forward current  becomes less than holding current, SCR turns from forward conduction state to forward  blocking state.

[Q-2] What is latching current in SCR?
It is the minimum current required to latch(turn on) the SCR from forward blocking state to forward conduction state.

[Q-3] What are the different turn on methods of SCR?
Forward voltage triggering
Gate Triggering
dv/dt triggering
Temperature triggering
Light triggering

[Q-4] What is snubber circuit?
The snubber circuit is used for the dv/dt protection of the SCR. It is a series combination of a resistor and a capacitor in parallel with the SCR.

[Q-5] What is hard switching of the thyristor?
When gate current is several times higher than the required gate current, the SCR is said to be hard fired. It reduces the turn ON time and enhances the di/dt capability.

[Q-6] What is firing angle?
The angle between the zero crossing of the input voltage and the instant the SCR is fired is called as delay angle or firing angle.

[Q-7] What is meant by SOA?
SOA – Safe Operating Area determines the voltage and current boundary within which the Power Device can be operated without destructive failure.

[Q-8] What are the main components used for isolating the Power Circuits, Power Semiconductor from the low-power circuit?
Opto-Couplers, Transformers

[Q-9]  Name some of the current controlled (current driven) devices…
SCR,  GTO,  GTR 

[Q-10] Name some of the voltage driven ( Voltage controlled) devices
IGBT, MCT, IGCT, SIT 

[Q-11] What is duty cycle?
It is the ratio of the ON time of the chopper to total time period of the chopper.
D = Ton / [Ton + Toff]

[Q-12] Can fuses with an AC voltage rating be used in a DC applications?
Fuses must be rated for the voltage AC or DC in which they will be used.
Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating.

[Q-13] What are the characteristics of ideal Opamp?
Infinite open loop voltage gain
Infinite input impedance
Zero output impedance
Infinite Bandwidth
Zero offset voltage

[Q-14] For High voltage applications will you prefer MOSFET or IGBT?

• For High voltage applications we have to use IGBT.
• Because MOSFETs are low voltage devices. ie, Their voltage rating is lesser than IGBT.
• General rule is MOSFETs are suitable for applications which has breakdown voltage less than 250V.
• The IGBTs are suitable for applications which has breakdown voltage upto 1000V.

[Q-15] For High frequency applications will you prefer MOSFET or IGBT?  Why?

• For High frequency applications, MOSFET is the right choice of the device.
• Because MOSFET has low switching losses compare to that of IGBT.
• General rule of thumb is for low-frequency applications having frequency range upto 20kHz, we have to use IGBT.
• For high frequency applications having frequency range of more than 200kHz, we have to use MOSFET.

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                                                                                               -- Bellapuri saikumar
                                                                                                         ( sai saikumar jn)