No. of Pages: 2
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
SECOND SEMESTER M.TECH DEGREE EXAMINATION, MAY 208
Electrical and Electronics Engineering
(Power Control and DHives)

01 EE6502: Design Principles ofPower Converters

Max. Marks: 60 Duration: 3 Hours
Answer any two questionsfrom each part.
PARTA
1. Design an inductor for buck converter configuration with the following

specifications:

Output voltage, Vo > ۷

Output current, 10 = 5A

Switching frequency, fs = 20 kHz Input
voltage, Vi= |

Diode voltage drop, VF IV

Operating flux density, Bac=O.05T

Window utilization factor, Ku=C.29 9 marks
Current density, J=433 A/cm |

A dc chopper has a MOSFET switch that dissipates 40W and load free wheel
diode that dissipates 20W. Both devices are mounted on a common heat
sink. The MOSFET has junction to case thermal resistance of

0.7K]W and case to heat sink thermal resistance of 0.5K/W. The diode has
junction to case thermal resistance of 0.8K/W and case to heat sink thermal
resistance of 0.6K/W.

a) Determine the maximum heat sink thermal resistance that maintains

both junction temperatures below 90°C in an ambient of 30°C. (6 marks)

b) Semiconductor lifetime approximately doubles for every 0 © decrease in
junction temperature. If the heat sink in the previous case
is fan cooled, estimate the lifetime improvement if the heat sink
(3 marks) thermal impedance is halved with fan cooling.