Thursday, September 13, 2012

Power Electronics Objective Questions with Answers: Part-3

[1] The breakdown mechanism in a lightly doped p-n junction under reverse biased condition is called
(a) Avalanche breakdown
(b) Zener breakdown
(c) Breakdown by tunneling
(d) High voltage breakdown

[2] For a large values of |VDS|, a FET behave as
(a) Voltage controlled resistor
(b) Current controlled current source
(c) Voltage controlled current source
(d) Current controlled resistor

[3] In a full wave rectifier without filter, the ripple factor is
(a) 0.482
(b) 1.21
(c) 1.79
(d) 2.05

[4] Space charge region around a P-N junction
a. Does not contain mobile carries
b. Contains both free electrons and holes
c. Contains one type of mobile carriers depending on the level of doping of the P or N regions
d. Contains electrons only as free carriers

[5] In a JFET, at pinch-off voltage applied on the gate
a. The drain current becomes almost zero
b. The drain current begins to decrease
c. The drain current is almost at saturation value
d. The drain to source voltage is close to zero volts

[6] The value of ripple factor of a half wave rectifier without filter is approximately
a. 1.2
b. 0.2
c. 2.2
d. 2.0

[7] In an intrinsic semiconductor, the Fermi-level is
a. Closer to the valence band
b. Midway between conduction and valence band
c. Closer to the conduction band
d. Within the valence band

[8] The transformer utilization factor of a half wave rectifier is approximately
a. 0.6
b. 0.3
c. 0.9
d. 1.1

[9] Transistor is a 
a. Current controlled current device
b. Current controlled voltage device
c. Voltage controlled current device
d. Voltage controlled voltage device

For ex, the output current Ic depends on the input current Ib
[10] If the output voltage of a bridge rectifier is 100V, the PIV of diode will be
a. 100√2 V
b. 200/π V
c. 100π V
d. 100/2 V

Peak Inverse Voltage = Max  Secondary Voltage = Vdc= 2Vm/π = 100
Vm = 100π/2
[11] The thyristor can be brought to forward conducting state with gate-circuit open when the applied voltage exceeds
(a) The forward breakover voltage
(b) Reverse breakdown voltage
(c) 1.5V
(d) Peak non-repetitive off-state voltage

[12] In a SCR, the holding current is

(a) More than latching current 
(b) Less than latching current 
(c) Equal to latching current 
(d) Very small

[13] When a SCR gets turned on, the gate drive

(a) Should not be removed as it will turn off the SCR
(b) May or may not be removed
(c) Should be removed
(d) Should be removed in order to avoid increased losses and higher junction temperature.

[14] For the normal SCR, the turn on time is

(a) Less than turn-off time 
(b) More than turn-off time 
(c) Equal to turn-off time 
(d) Half of turn-off time

[15] The forward voltage drop during SCR ON state is 1.5V. This voltage drop

(a) Remains constant and is independent of load current
(b) Increases slightly with load current
(c) Decrease slightly with load current
(d) Varies linearly with load current

4:32 PM

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