Power Electronics Mid - I, September - 2014

1.An SCR is a
  • Three-layer three terminal device
  • Three-layer four terminal device
  • four-layer three terminal device
  • four-layer four terminal device
Answer: C
2.For an SCR, dv/dt protection is achieved by
  • RC in series with SCR
  • RC across SCR
  • RL in series with SCR
  • L in series with SCR
Answer: B
3.The SCR ratings di/dt in A/sec and dv/dt in V/sec may vary respectively between
  • 20 to 500, 10 to 100
  • both 20 to 500
  • both 10 to 100
  • 50 to 300, 20 to 500
Answer: B
4.In a thyristor ratio of holding current to latching current__________
  • 0.4
  • 2.5
  • 1
  • 0.25
Answer: A
5.For an UJT employed for the triggering of an SCR, Stand-off ratio  = 0.64 and dc source voltage VBB = 20V .The UJT would trigger when the emitter voltage is
  • 12.8v
  • 13.5v
  • 10v
  • 5v
Answer: B
6.When a thyristor is reverse biased the number of blocked p-n junction is ________
  • 1
  • 2
  • 3
  • 4
Answer: B
7.In a single phase semi converter for continuous conduction freewheeling diode conducts for
  • α
  • π- α
  • π
  • π - α
Answer: A
8.A 1-φ midpoint thyristor of full wave uses a 230/220v transformer with center tap on the secondary side. The PIV per thyristor is
  • 100v
  • 141.4v
  • 200v
  • 282.2v
Answer: D
9.In a single phase full converter, for continuous conduction, each pair of SCRs conduct for
  • α
  • π- α
  • π
  • π- α
Answer: C
10.Two transistors connected back to back is called
  • SCR
  • MOSFET
  • IGBT
  • ALL THE ABOVE.
Answer: A
11.In a thyristor anode current is made of ________ and ________
Answer: eletrons, holes
12.During forward blocking state, the thyristor is associated with __________
Answer: high voltage, less current
13.The most suitable device for high frequency inversion in SMPS is __________
Answer: MOSFET
14.The process of bringing an ON thyristor to its OFF state by another thyristor is called ______
Answer: forced commutation
15.The diode in a RL load full converter is used for ___________________
Answer: flow of freewheeling current
16.In case of series contribution SCR’s string efficiency is less due to ___________ distribution.
Answer: unequal voltage
17.Snubber circuit is used for ______ protection.
Answer: dv/dt
18.A1-φ half wave converter feeding with resistive load the average output voltage is ________
Answer:
19.A Thyristor may be turned as ________ swich.
Answer: DC
20.During the overlapping period, the output voltage of a 1-φ fully controlled Bridge rectifier is ________
Answer: Zero