K is the Boltzmann constant
e is the charge on the electron
T is the absolute temperature.
12. Device with highest d(i)÷d(t) and d(v)÷d(t) capability is _____________
A. GTO
B. BJT
C. SCR
D. SITH
Answer: D
SITH stands for static induction thyristor. It has a buried gate structure in which the gate electrode is placed in the n-base region. They have high d(i)÷d(t) and d(v)÷d(t) capability.
13. ____________ is the switching frequency of SITH.
A. 55 kHz
B. 100 kHz
C. 91 kHz
D. 105 kHz
Answer: B
100 kHz is the switching frequency of the static induction thyristor. Static Induction Thyristor has a low frequency because of lower turn-off current gain.
14. Calculate the value of the Crest factor if Vpeak=1.5 V and Vr.m.s=2.5 V.
A. .4
B. .6
C. .5
D. .7
Answer: B
The value of the crest factor is
Vpeak÷Vr.m.s=1.5÷2.5=.6 V.
It signifies the peak value is .6 times than the r.m.s value.
15. Calculate the output voltage of the Boost converter if the supply voltage is 1 V and the duty cycle value is .9.
A. 10 V
B. 20 V
C. 40 V
D. 60 V
Answer: A
The output voltage of the buck converter is
Vo = Vin×(D)
The value of the duty cycle is less than one which makes the Vo < Vin. Vo = Vin×(1-D)=10 V.
16. Calculate the value of the safety factor using the data: tc=12 msec, tq=6 msec.
A. 4
B. 2
C. 3
D. 6
Answer: B
The value of the safety factor is the ratio of the circuit turn-off time and device turn-off time.
S.F=tc÷tq=12÷6=2.
17. For successful commutation circuit turn-off time ______ device turn-off time.
A. <
B. >
C. =
D. ~
Answer: B
For a successful commutation circuit, the turn-off time must be greater than the device turn-off time. The excess stored charged carriers should be removed from the gate junction in order to avoid false triggering.
18. SCR is a __________ device.
A. Uncontrolled
B. Semi-controlled
C. Fully controlled
D. Voltage
Answer: B
The SCR is a semi-controlled device. Turn-on time can be controlled by using a gate pulse but a commutation circuit is required to turn off the device.
19. Holding current of the SCR is ___________
A. > than latching current
B. < than latching current
C. = to latching current
D. ≥ than latching current
Answer: B
The holding current of the SCR is less than the latching current. The value of latching current is 2-3 times that of holding current.
20. If the holding current of an SCR is 6 mA then its latching current should be ___________
A. 4 mA
B. 5 mA
C. 12 mA
D. 6 mA
Answer: C
If the holding current of an SCR is 6 mA then its latching current should be 12 mA. The latching current is 2-3 times more than the holding current.