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Online Electronics and Communication Engineering Test - Power Electronics Test

Instruction:
  • This is a FREE online test. Beware of scammers who ask for money to attend this test.
  • Total number of questions: 20.
  • Time allotted: 30 minutes.
  • Each question carries 1 mark; there are no negative marks.
  • DO NOT refresh the page.
  • All the best!

Marks : 2/20

Total number of questions
20
Number of answered questions
0
Number of unanswered questions
20
Test Review : View answers and explanation for this test.
1.
For a BJT a = 0.98, then β =
0.02
0.5
4.9
49
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

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2.
The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes
about 100 times
about 10 times
about 3 times
about twice
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

v ∝ (i)1/4 ∝ (100)1/4 ≈ 3.

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3.
The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode)
limits charging current
limits discharging current
limits both charging and discharging currents
none of the above
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

Discharge current flows through Re .

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4.
The rated current of a thyristor is 40 A. The holding current will be about :
20 A
1 A
100 mA
10 mA
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

The holding current is much less then 1% of rated current.

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5.
A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a. During one cycle of input voltage, the total duration of conduction of freewheeling diode is
a
2 a
4 a
0.5 a
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

Freewheeling diode conducts for a° in each half cycle.

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6.
An SCR has a turn on time of 4 μs. The gate pulse should have a duration of about
2 μs
5 μs
20 μs
50 μs
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

Duration of gate pulse should be slightly more than turn time of SCR.

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7.
A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ωt. The thyristor will conduct
from 0 to 180°
when v > 50 V
from 0 to 90°
When v < 50 V
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

Thyristor can conduct only when it is forward biased. This occurs only when v > 50 V.

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8.

Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V.

Reason (R): When an SCR is conducting, the junction temperature is about 200°C.

Both A and R are correct and R is correct explanation of A
Both A and R correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Your Answer: Option
(Not Answered)
Correct Answer: Option
Explanation:

Junction temperature is about 120°C. Hence R is wrong.

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9.
If 4 quadrant operation is required we need
dual converter
full converter
semi converter
none of the above
Your Answer: Option
(Not Answered)
Correct Answer: Option
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10.
A chopper cannot be line commutated.
True
False
Your Answer: Option
(Not Answered)
Correct Answer: Option
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11.
In a parallel inverter
each thyristor is turned on twice during each cycle
each thyristor is turned on once during each cycle
each thyristor is turned on either once or twice in each load cycle
each thyristor may be turned on upto four times in each load cycle
Your Answer: Option
(Not Answered)
Correct Answer: Option
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12.
In thermal ohm's law, temperature and power loss are analogous to
V and I respectively of ohm's law
I and V respectively of ohm's law
R and V respectively of ohm's law
I and R respectively of ohm's law
Your Answer: Option
(Not Answered)
Correct Answer: Option
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13.
The output frequency of a cycloconverter can be changed by changing the firing angle.
True
False
Your Answer: Option
(Not Answered)
Correct Answer: Option
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14.
The difference between resonant commutation and self commutation is
both these methods are based on entirely different principles
in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current
resonant commutation uses L and C but self commutation uses only capacitor
none of the above
Your Answer: Option
(Not Answered)
Correct Answer: Option
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15.
A TRIAC can be turned on :
by applying a positive signal to gate
by applying a negative signal to gate
by applying either positive or negative signal to gate
none of the above
Your Answer: Option
(Not Answered)
Correct Answer: Option
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16.
In auxiliary commutated chopper, the peak value of thyristor current is
equal to peak value of load current
equal to peak value of capacitor current
sum of peak value of load current and capacitor current
none of the above
Your Answer: Option
(Not Answered)
Correct Answer: Option
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17.
Which chopper circuit operates in quadrants 1 and 4?
A
B
D
E
Your Answer: Option
(Not Answered)
Correct Answer: Option
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18.

Assertion (A): A fully controlled bridge converter can operate in first and fourth quadrant.

Reason (R): A semi converter is cheaper than a full converter.

Both A and R are correct and R is correct explanation of A
Both A and R correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Your Answer: Option
(Not Answered)
Correct Answer: Option
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19.
The output wave of a cycloconverter consists of a number of segments derived from the input wave.
True
False
Your Answer: Option
(Not Answered)
Correct Answer: Option
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20.
A single phase cycloconverter with centre tapped input transformer requires
2 thyristors
4 thyristors
8 thyristors
either 2 or 4 thyristors
Your Answer: Option
(Not Answered)
Correct Answer: Option
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