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WorksheetsPower Electronics Quiz 1
Total questions: 20
Worksheet time: 11mins
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
The dv/dt capability of an SCR can be improved by:
Increasing gate current
Using RC snubber circuit
Reducing load inductance
Operating at higher temperature
What happens if a MOSFET is operated in the linear region for extended periods?
Device efficiency improves
Switching speed increases
Excessive power dissipation and heating
Voltage rating increases
In IGBT switching characteristics, the turn-on delay time is primarily due to:
Gate capacitance charging
Minority carrier injection
Channel formation time
Parasitic inductance
In natural commutation of SCR:
External circuit forces the current to zero
Load current naturally becomes zero
Gate signal is removed
Supply voltage is reversed
Which of the following is a unidirectional current, unidirectional voltage device?
TRIAC
SCR (Thyristor)
DIAC
GTO
IGCT differs from conventional GTO mainly in:
Turn-on capability
Integrated gate drive unit for improved turn-off
Voltage blocking capability
Current rating
The main limitation of BJT in high-power switching applications is:
Low voltage rating
Current driven device requiring continuous base current
Poor thermal characteristics
High switching losses only
A snubber circuit across a switching device primarily protects against:
Overcurrent during turn-on
Overvoltage during turn-off
Both voltage and current transients
Thermal runaway
In a thyristor family, the device that can be turned on by light and turned off by reverse gate current is __________, while the device that can conduct in both directions and be triggered by either polarity gate signal is __________. (use short forms)
(a)
The __________ time of a power MOSFET is the time interval between the gate voltage reaching 10% of its final value and the drain current reaching 90% of its final value, while the __________ effect causes the gate drive current to temporarily reverse during switching transitions.
(a)
