Power Electronics & Drives.pdf - POWER ELECTRONICS...

POWER ELECTRONICS
INTERVIEW QUESTIONS
Engineering Funda YouTube Channel
By. Prof. Hitesh Dholakiya
SSASIT, Surat

ENGINEERING FUNDA YOUTUBE CHANNEL BY PROF. HITESH DHOLAKIYA
POWER ELECTRONICS INTERVIEW QUESTIONS
Q-1 Why IGBT is very popular nowadays?
Ans a. Lower hate requirements
b. Lower switching losses
c. Smaller snubber circuit requirements
Q-2 What are the different methods to turn on the thyristor?
Ans a. Forward voltage triggering
b. Gate triggering
c. dv/dt triggering
d. Temperature triggering
e. Light triggering
Q-3 What is the difference between power diode and signal diode?
Ans Power diode
1. Constructed with n-layer, called drift region between p+ layer and n+ layer.
2. The voltage, current and power ratings are higher.
3. Power diodes operate at high speeds.
Signal diode
1. Drift region is not present.
2. Lower
3. Operates at higher switching speed.
Q-4 IGBT is a voltage controlled device. Why?
Ans Because the controlling parameter is gate-emitter voltage.
Q-5
Power MOSFET is a voltage controlled device. Why?
Ans Because the output (drain) current can be controlled by gate-source voltage.
Q-6 Power BJT is a current controlled device. Why?
Ans Because the output (collector) current can be controlled by base current.
Q-7 What are the different types of power MOSFET?
Ans a. N-channel MOSFET
b. P-channel MOSFET
Q-8 How can a thyristor turned off?
Ans A thyristor can be turned off by making the current flowing through it to zero.
Q-9
Define latching current.
Ans The latching current is defined as the minimum value of anode current which it
must attain during turn on process to maintain conduction when gate signal is
removed.
Q-10 Define holding current.
Ans The holding current is defined as the minimum value of anode current below
which it must fall to for turning off the thyristor.
Q-11
What is a snubber circuit?
Ans It consists of a series combination of a resistor and a capacitor in parallel with
the thyristors. It is mainly used for dv / dt protection
Q-12
What losses occur in a thyristor during working conditions?
Ans a. Forward conduction losses
b. Loss due to leakage current during forward and reverse blocking.
c. Switching losses at turn-on and turn-off.
d. Gate triggering loss.
Q-13 Define hard-driving or over-driving.

ENGINEERING FUNDA YOUTUBE CHANNEL BY PROF. HITESH DHOLAKIYA
POWER ELECTRONICS INTERVIEW QUESTIONS
Ans When gate current is several times higher than the minimum gate current
required, a thyristor is said to be hard-fired or over-driven. Hard-firing of a
thyristor reduces its turn-on time and enhances its di/dt capability.
Q-14 Define circuit turn off time.
Ans It is defined as the time during which a reverse voltage is applied across the
thyristor during its commutation process.
Q-15 Why circuit turn off time should be greater than the thyristor turn-off
time?