A buck converter is operated from the rectified 230 V ac mains,such that the converter de input voltage
IS
V8 = 325 v ± 20%
A control circuit automatically adjusts the converter duty cycleD,to maintain a constant de output voltage
of V = 240 V de. The de load current I can vary over a 10: 1range:
lOA::;J:s;lA
The MOSFET has an on-resistance ofO.S Q. The diode conduction losscan be modeled by a 0.7 V
source in series with a 0.2 Q resistor. All other losses can beneglected.
(a) Derive an equivalent circuit that models the converter inputand output ports, as well as the loss
elements described above.
(b) Given the range of variation of V8 and I described above, overwhat range will the duty cycle
vary?
(c) At what operating point (i.e., at what value of V8 and I) isthe converter power loss the largest?
What is the value of the efficiency at this operating point?
