Power factor preregulators based on combined buck-flyback topologies

The limitation imposed on the achievable power level by the IEC 1000-3-2 standard in buck-derived power factor preregulators, is overcome by using a combined buck-flyback power stage. Two different step-down converters are proposed in this paper, which incorporate an auxiliary flyback stage. The auxiliary stage uses the same switch of the main converter, plus an additional power switch commutated at the line frequency. As compared to a simple buck rectifier, with this solution the harmonic content of the absorbed line current, at a given power level, can be reduced, thanks to the resulting increased conduction angle of the input rectifier bridge. Experimental results based on a 1 kW prototype are reported to validate the theoretical analysis of the proposed topologies.