MCQs on Power Electronics

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01․ Leakage current flows through the thyristor in
forward blocking mode.
reverse blocking mode.
both forward and reverse blocking mode.
forward conduction mode.

In forward blocking mode junction J2 and in reverse blocking mode junction J1 and J3 act as a capacitor hence leakage current present in both mode.

02․ Which triggering is the most reliable?
Forward voltage triggering.
Gate triggering.
dV / dt triggering.
Thermal triggering.

Gate triggering process is the most reliable as junction temperature does not rise to high value in this process.

03․ Light triggering mainly used in
low - voltage direct current transmission.
medium voltage direct current transmission.
high voltage direct current transmission.
all of these.

Light triggering combined with gate triggering mainly used in HVDC as this combination is very powerful triggering process.

04․ In a P1N1P2N2 thyristor which layer is less doped ? width=176

H2 ⇒ Highly doped. P2 ⇒ Less highly doped. N1 ⇒ Less doped. P1 ⇒ Same as P2.

05․ If a latching current for the circuit shown in figure is 2 mA. Obtain the value of minimum width of the property turn ON the SCR? mcq-power-electronics-8
3 µs.
3.1 µs
3.2 µs
3.3 µs


06․ Let of a thyristor Vc1, Vc2, Vc3 are forward break over voltage for gate current Ig1, Ig2, Ig3 respectively. Then
Vc1 > Vc2 > Vc3 when Ig1 >
Vc1 > Vc2 > Vc3 when Ig1 < Ig2 < Ig3.
Vc1 = Vc2 = Vc3 any value of Ig.
Vc1 > Vc2 > Vc3 when Ig1= Ig2

If gate current is increased then thyristor will shift from forward blocking mode to forward conducting mode at a lower voltage.

07․ SCR will be turned off when anode current is
< latching current but greater than holding current and gate signal is 0.
less than holding current.
< latching current but greater than holding current and gate signal is present.
both (A) and (B).

When anode current is in between holding current and latching current then SCR is off only if gate signal is absent. When anode current is below holding current then it is properly turned off.

08․ After proper turn on of thyristor
gate signal is always present.
gate signal must be removed.
gate signal should present but can be removed.
none of the above.

After proper turn on of thyristor gate signal must be removed to reduce the loss in gate circuit.

09․ Gate circuit or triggering circuit of a thyristor is
lower power circuit.
high power circuit.
may be low power or high power circuit.

Thyristor circuit is high power circuit. But its triggering circuit is low power circuit.

10․ A thyristor will be triggered when Vg = 1.5 volt and Ig = 100 mA in the given figure. Calculate the value of R in ohm is mcq-power-electronics-9