MCQs on Power Electronics

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01․ Rise time is defined by the interval when
gate current rises from 90 % to 100 % of it final value.
anode voltage drops from 90 % to 10 % of its initial value.
anode current rises 10 % to 90 % of its final value.
both B and C.

Rise time is known as the time interval when anode voltage drops from 90 % to 10 % of its initial value. At the same time anode current rise 10 % to 90 % of its final value.
02․ Spread time is defined as the interval during which
anode voltage drops from 10 % of its initial value to zero.
anode current rises from 90 % to its final value.
both (A) and (B).
anode current rises from 10 % to 90 % of its final value.

Voltage across SCR never comes down to zero. There is always a ON state voltage drop present across SCR.
03․ Maximum power loss occurs during
delay time.
rise time.
spread time.
all.

Only during rising time anode voltage and current simultaneously high. So power loss (V X I) is maximum here.
04․ The typical time of rising time lies between
10 - 20 µs.
40 - 60 µs.
1 - 4 µs.
90 - 100 µs.

Generally rise time is very low around 1 - 4 µs.
05․ During which time maximum conduction spreading take place in the thyristor during turn ON?
Delay time.
Spread time.
Rise time.
Same for every case.

During spread time maximum charges spread across the thyristor.
06․ During reverse recovery time
charge carrier of junction J2 recombined.
charge carrier of junction J1 is swept out.
charge carrier of junction J3 is swept out.
both B and C.

During reverse recovery time free charge carriers swept out from the junction J1 and J3.
07․ During gate recovery time
charge carriers of J2 junction recombined.
charge carriers of J2 junction is swept out.
charge carrier of J1 junction removed.
charge carriers of J3 junction is removed.

Charges at J2 junction are trapped. So recombination is the only way to remove them.
08․ Typical range of thyristor turn OFF time is
3 - 10 µs.
3 - 50 µs.
3 - 100 µs.
3 - 500 µs.

Generally thyristor takes very short time to turn OFF in range 3 - 100 µs.
09․ Which statement is true ?
Reverse recovery time ( trr ) > gate recovery time (tgr).
Device turn OFF time ( tq ) > reverse recover time (trr).
Circuit turn OFF time > device turn OFF time ( tq ).
All of these.

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10․ ON state voltage drop across SCR lie between the range
0 - 0.5 V.
0.5 - 1 V.
1 - 1.5 V.
1.5 - 2 V.

ON-state voltage drop is very low around 1 - 1.5 V.
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