Electronics and Communication Engineering - Power Electronics


In a semi converter feeding a resistive load, the firing angle is a. Each thyristor conducts for

A. p radians
B. (p - a) radians
C. (p + a) radians
D. (p - 0.5 a) radians

Answer: Option B


The conduction is from a to p.


Between which points does UJT exhibit negative resistance characteristics

A. between peak and valley points
B. before peak point
C. after peak point
D. after valley point

Answer: Option A


No answer description available for this question. Let us discuss.


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

A. 2° C/W
B. 1.4° C/W
C. 0.7°C/W
D. 2.2° C/W

Answer: Option B




A single phase electric heater uses phase controlled thyristors. The firing angle is 90°. The degree of heating is

A. 25% of maximum
B. 50% of maximum
C. 75% of maximum
D. none of the above

Answer: Option B


Conduction occurs only during 50% of wave.


Which of these commutation methods is used in AC-DC converters?

A. Class A
B. Class C
C. Class D
D. Class F

Answer: Option D


Class F is natural commutation AC = DC converter use natural (or line) commutation.