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terça-feira, 19 de outubro de 2010

Switch Mode Power Supply Topologies, a Comparative Study

Switch Mode Power Supply Topologies, a Comparative Study
Khoo Ghim Wee

School of Science and Technology
A thesis submitted to SIM University in partial fulfillment of the requirements for the degree of Bachelor of Engineering
2009

Abstract
In the experiment, two isolated single-switch rectifiers are compared: one is based on the forward topology with third reset winding, the other is a flyback rectifier with a passive snubber. These rectifiers were both designed for universal input voltage range (90 - 260 VRMS) and 75 W nominal output power. The current mode control technique is adopted to provide over-power protection and provide feedback compensation to maintain stable output voltage. The comparison is based both on theoretical analysis and measurements on simulations and takes into account the following aspects: power losses on the main devices, overall efficiency, power factor and output ripple. This work highlights the advantages and drawbacks of both the selected topologies.
According to the IEC61000-3-2 standard, there is a need of an active circuitry to improve the Total Harmonic Distortion with a sacrifice of 5-10% of the overall efficiency and an improved PF of up to 0.99. In the simulation test results, the flyback converter adopting this active PFC circuit (NCP1653) shows to have a drop of about 3% of overall efficiency while the forward converter has a drop of about 6%. However, by using passive PFC, a LC filter idea is adopted to slightly improve both converters with a PF of 0.7-0.8 with lesser efficiency drop. In the efficiency tests, it is obvious forward converter has a better overall efficiency over flyback converter except during low output power. The power loss of both converters’ active devices such as the switching MOSFET and diode, can help to understand the root of the cause of the drop in the efficiency. The most power loss of the forward converter is the MOSFET while for the flyback converter is the snubber and transformer wire loss.

FULL THESIS HERE:http://www.4shared.com/document/Q_oE7xY4/Khoo_Ghim_Wee.html