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- Question
A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is
Options- A. 20 W
- B. 50 W
- C. 92 W
- D. 128 W
- Correct Answer
- 50 W
Explanation
.
Power Electronics problems
Search Results
- 1. Assertion (A): An ideal rectifier should have unity harmonic factor
Reason (R): An ideal rectifier should have unity displacement factor.
Options- A. Both A and R are correct and R is correct explanation of A
- B. Both A and R correct but R is not correct explanation of A
- C. A is correct but R is wrong
- D. A is wrong but R is correct Discuss
Correct Answer: A is wrong but R is correct
Explanation:
Ideal rectifier should have zero harmonic factor and unity displacement factor.- 2. In a thyristor the gate current is increased, then
Options- A. anode current will increase
- B. anode current will decrease
- C. anode current will remain constant
- D. anode current may increase or decrease Discuss
Correct Answer: anode current will remain constant
Explanation:
Gate current does not affect the magnitude of anode current.- 3. Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous
Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.
Options- A. Both A and R are correct and R is correct explanation of A
- B. Both A and R correct but R is not correct explanation of A
- C. A is correct but R is wrong
- D. A is wrong but R is correct Discuss
Correct Answer: A is correct but R is wrong
Explanation:
If duty cycle is low, current may become discontinuous.- 4. A chopper
Options- A. converts constant voltage dc into ac and then into variable voltage dc
- B. converts constant voltage dc into variable voltage dc directly
- C. converts ac of one frequency into ac of another frequency
- D. converts ac to dc Discuss
Correct Answer: converts constant voltage dc into variable voltage dc directly
Explanation:
A chopper is a dc-ac converter. It converts a fixed dc voltage into a variable dc voltage.- 5. Figure shows a chopper feeding RLE load, The free wheeling diode conducts when
Options- A. thyristor is on
- B. thyristor is off
- C. both when thyristor is on and thyristor is off
- D. partly when thyristor is off and partly when thyristor is on Discuss
Correct Answer: thyristor is off
Explanation:
FD is forward biased only when thyristor is off.- 6. The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes
Options- A. about 100 times
- B. about 10 times
- C. about 3 times
- D. about twice Discuss
Correct Answer: about 3 times
Explanation:
v ? (i)1/4 ? (100)1/4 ? 3.- 7. The number of leads in an SCR are :
Options- A. 2
- B. 3
- C. 4
- D. 5 Discuss
Correct Answer: 3
Explanation:
Anode, cathode and gate.- 8. Thyristors are not suitable for logic circuits.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Thyristors can be used for logic circuits.- 9. A cycloconverter can be
Options- A. step down
- B. step up
- C. step down or step up
- D. none of the above Discuss
Correct Answer: step down or step up
Explanation:
The output frequency can be more or less than input frequency.- 10. For a 12 pulse operation, the two 6 pulse units are fed by
Options- A. Y - Y and Y - Y transformers
- B. ? - ? and ? - ? transformers
- C. Y - Y and Y - ? transformers
- D. Y - ? and Y - ? transformers Discuss
Correct Answer: Y - Y and Y - ? transformers
Explanation:
30° phase difference is necessary.
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- 1. Assertion (A): An ideal rectifier should have unity harmonic factor