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Unformatted text preview: Spring 2011 EEE472/591 – Power Electronics and Power
Due: Tuesday, April 5 Raja Ayyanar Problem 1: (25 points)
A power supply manufacturer has a large stock of 500 V MOSFETs and would like to use them
in a forward converter (shown below) of the following specifications:
Vin : 100V 130 V ; Vo : 3.3V ; I o.max : 100 A . To provide sufficient safety margin, it is desired
to limit the maximum voltage across the above MOSFET to 400 V.
+ n pri Vin Vo nsec - - nreset + D (a) Calculate the turns ratio, n pri : n reset such that the above requirement on maximum MOSFET voltage is satisfied, while simultaneously maximizing the allowable duty ratio. What is the
maximum value of duty ratio?
(b) Calculate the turns ratio, n pri : n sec . (c) Neglecting the magnetizing current, what is the peak current rating for the MOSFET?
Problem 2 (25 points):
Corresponding to the flyback converter given below, sketch the waveforms of v pri , i pri and isec
indicating relevant magnitudes and slopes. Assume CCM. i pri +
Vo = 100V
_ 1: 0.5 isec I o = 10 A
_ Vo = 50V
L pri = 100 m H
f sw = 200 kHz Problem 3: (25 points)
Design a full-bridge dc-dc converter corresponding to the following specifications.
(Give transformer turns-ratios, RMS current rating of transformer primary winding, and output
inductance and maximum ESR values for both the outputs)
Vin : 200V to 400V
Vo,1 : 5V , I o,1 max 20 A, I o,1 min 4 A
Vo ,2 : 12V I o ,2 : 1A (constant load )
Vo,1 50mV , I L ,1 2 A Optional extra credit problem (25 points)
Simulate the flyback converter of Problem 2 using PLECS or PSpice and show the waveforms
required in Problem 2 from the simulation. Show the schematic also with all the parameter
values clearly shown. ...
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