POWER ELECTRONICS QUIZ

A diac has ___________ pn junctions

None of these

Two

Four

Three

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The turn-on time of an SCR with inductive load is 20 µs. The puls train frequency is 2.5 KHz with a mark/space ratio of 1/10, then SCR will

Turn on if inductance is removed.

Turn on if pulse frequency us increased to two times.

Not turn on.

Turn on.

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To meet high current demand we use SCRs in

both B and C.

series connection.

parallel connection.

anti parallel connection.

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In reverse blocking mode of a thyristor

junction J1, J3 is in reverse bias and J2 is in forward bias.

junction J3 is in forward bias and J1, J2 in reverse bias.

junction J1 and J2 is in forward bias and J3 is in reverse bias.

junction J2 is in reverse bias and J1, J3 is in forward bias.

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When a large surge current of very short duration flows through a thyristor then which one of the following device will operate to protect the thyristor ?

Snubber circuit.

CB.

Voltage clamping device.

Fast acting current limiting device (FACL fuse).

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Anode current in an SCR consists of

electrons only.

either electron or holes.

holes only.

Both electron and holes.

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Thyristor can be protected from over voltages by using

heat sink.

fuse.

snubber circuit.

voltage clamping device.

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A UJT is sometimes called ___________ diode.

Single-base

Low resistance

Double-base

High resistance

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A single phase one pulse controlled circuit has a resistance R and counter emf E load 400 sin(314 t) as the source voltage. For a load counter emf of 200 V, the range of firing angle control is

30° to 180°.

60° to 180°.

30° to 150°.

60° to 120°.

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Between the peak point and the valley point of UJT emitter characteristics we have ___________ region

None of these

Negative resistance

Saturation

Cut-off

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