A thyristor has maximum allowable junction temperature of 110° C and the ambient temperature is 40°C, If the maximum internal power dissipation is 50 W, the thermal resistance is
Options
A. 2° C/W
B. 1.4° C/W
C. 0.7°C/W
D. 2.2° C/W
Correct Answer
1.4° C/W
Explanation
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Power Electronics problems
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1. Assertion (A): A high dv/dt may cause triggering of a thyristor.
Reason (R): A high dv/dt results in charging current in the thyristor.
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
Correct Answer: Both A and R are correct and R is correct explanation of A
Explanation:
Since voltage across capacitor cannot change instantaneously it protects SCR against high .
6. A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be
In this case synchronous speed at 50 Hz is 1500 rpm. Therefore synchronous speed at 25 Hz is 750 rpm. Since slip is about 3 - 5%, speed is about 720 rpm.
7. To protect an SCR against high di/dt we connect
Regulation is possible only in positive half cycle.
9. A thyristor has internal power dissipation of 40W and is operated at an ambient temperature of 20°C. If thermal resistance is 1.6° C/W, the junction temperature is
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