ECE 481/523 Homework #3 - Due 9/19/2007 (Wed) Fall 2007
1. Problem 5.1 in Mohan
2. Problem 5.11 in Mohan
3. Problem 5.23 in Mohan
4. The circuit shown below resembles one that we studied in class to demonstrate the basic
principles of power electronics. However, the relative positions of the diode, inductor, and
switch are different from the class example. Assume the ideal inductor is very large such
that its current is continuous. The ideal capacitor is also very large so that its voltage is
essentially constant. Assume the diode is an ideal diode with zero forward voltage drop. The
ideal switch closes for 25 µsec and opens for 75 µsec during each cycle. The circuit has
achieved steady state conditions and the output voltage v
o
is assumed constant.
200 V R
+
-
v
L
i
o
v
D
v
C
v
o
-
-
-
-
++
++
C
L
i
C
i
D
D
v
S
i
S
i
L
(a) Calculate the duty cycle d for this circuit.
(b) Calculate the average value of the inductor voltage, V
L
.
(c) Calculate the average value of the capacitor current, I
C
.
(d) Determine the value of the inductor voltage when the switch is closed (ON).
(e) Determine the value of v
L
when the switch is open (OFF)
(Hint: Use answer to part b).
(f) Sketch v
L
(t) for at least one complete cycle.
(g) Determine the value of the output voltage v
o
when the switch is open (OFF).