Power Electronics Quiz 1

An SCR is conducting with anode current of 50 A. If the gate signal is suddenly removed, the SCR will:

• Turn off immediately

• Continue conducting if anode current > holding current

• Turn off after the storage time

• Conduct only for one more cycle

For an SCR with latching current IL = 40 mA and holding current IH = 30 mA, which statement is correct?

• Gate pulse width must ensure anode current ≥ 40 mA before gate is removed

• Anode current must be maintained above 30 mA to keep SCR conducting

• Both statements are correct

• Neither statement is correct

A MOSFET is preferred over BJT in high-frequency switching because:

• MOSFET has lower on-state voltage drop

• MOSFET has no minority carrier storage time

• MOSFET has higher current gain

• MOSFET has better thermal stability

In a TRIAC, if MT2 is positive and gate receives a negative pulse, the device will:

• Not turn on

• Turn on in quadrant I operation

• Turn on in quadrant II operation

• Turn on in quadrant III operation

The main reason for current tail in IGBT during turn-off is:

• Gate capacitance discharge

• Parasitic BJT cannot turn off instantly

• High dv/dt across the device

• Inductive load current

If an SCR has a holding current of 20 mA and the load current is 15 mA, what will happen?

• SCR will turn on normally

• SCR will not turn on even with gate trigger

• SCR will turn on but immediately turn off

• SCR will conduct with reduced efficiency

Which statement about GTO is correct?

• It can be turned on by positive gate current only

• It can be turned off by removing gate current

• It requires negative gate current for turn-off

• It has the same structure as SCR

The switching speed of a power MOSFET is primarily limited by:

• Channel resistance

• Gate drive circuit and internal capacitances

• Drain-source voltage

• Temperature variations

In forced commutation of SCR, the commutating capacitor is initially charged to:

• Zero voltage

• Supply voltage with same polarity

• Supply voltage with reverse polarity

• Half the supply voltage

IGBT combines the advantages of:

• High input impedance of MOSFET and low on-state drop of BJT

• Fast switching of BJT and high voltage capability of MOSFET

• Low cost of BJT and high frequency operation of MOSFET

• High current capability of SCR and voltage control of MOSFET