Abstract

Advanced telecommunication and computer systems demand high efficiency and high power density, distributed power supplies. Both the flyback and forward converter topologies are good candidates for these applications, owing to their simple circuitry. These topologies, however, require practical performance improvements. Improved zero voltage switching (ZVS) flyback and forward dc/dc converter topologies are developed in this thesis. They employ an auxiliary circuit, with only a few small components and switching devices, to achieve ZVS of the main switch. Steady state analyses are performed and show that the proposed topologies have the following merits: lossless switching of the main switch independent of the line and load conditions, no increase in conduction losses, simple power and control circuitry, and capability of operating in either voltage or current mode control. The small signal analysis and closed loop stability of the proposed topologies are also derived. The resulting compensation required for stable operation is obtained and shown to be straightforward. The steady state and small signal analyses are verified on a 50W prototype flyback converter switching at 200 kHz, and on a 100 W prototype forward converter switching at 300 kHz, respectively. Experimental results show that both the flyback and forward converters have about 5 to 7% higher efficiencies than the conventional hard switching converters for typical efficiencies of 70% and 85%, respectively. These topologies can therefore advantageously replace existing power supplies in advanced telecommunications and computer applications.