ECE 481/523 Fall 2007
Homework #2 – Due Wednesday, September 12
1. A non-ideal power semiconductor switch is used in a switching dc power supply. The
switch’s leakage current is negligible. This unique switch has voltage and current waveforms as
shown below.
450 V
120 V
2 V
100 V
450 V
0.0 A
10 A
40 A
20 A
0.0 A
OFF ON OFF
Switching
ON
Switching
OFF
10 usec 20 usec
(a) The overall thermal resistance between the switch’s junction and ambient air is 0.25
°C/W. What is the maximum average power dissipation permissible in this switch if
the junction temperature cannot exceed 125°C for an ambient temperature of 50°C?
(b) If the switch has a duty factor of 0.5, what is the average conduction loss over a
complete switching period?
(c) What is the maximum switching frequency at which the switch can operate given the
constraints in part(a) and part (b) with the given voltage and current profiles shown in
the figure?
2. Problem 3.3 in Mohan text. Only for Figure P3-3 (a), (e).
3. Problem 3.4 in Mohan text. Only for Figure P3-3 (a), (e).
4. Problem 3.5 in Mohan text. Only for Figure P3-3 (a), (e).