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Improving the Low Power Operation of Full-Bridge Single-Stage Power Factor Correctors

Ribeiro, H.R. ; Borges, B.

Improving the Low Power Operation of Full-Bridge Single-Stage Power Factor Correctors, Proc IEEE Energy Conversion Congress and Exposition - ECCE, Raleigh, United States, Vol. -, pp. - - -, September, 2012.

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Full-Bridge Single Stage, FBSS, Switch Mode Power Supplies, SMPS, realize two conversion processes, in order to regulate the output voltage and the input current using only the four bridge transistors. This single stage characteristic introduces various limitations in the FBSS operation. The regulation of the output voltage implies the existence of a minimum conduction time of the bridge transistors, which inevitably will result in a minimum input power that must be surpassed in the output. Otherwise the input current and the DC bus voltage will remain incontrollable. This fact introduces some restrictions in the input and output inductors design: normally a high value input inductor is needed to avoid the operation of the output filter in DCM with high power. In order to solve this problem, a new solution consisting in a Free Wheeling Circuit, FWC, is proposed in this paper. The concept allows the operation with light load, without imposing any restriction to the input and output inductors. This is due to the fact that the FWC allows to discharge the DC bus capacitor avoiding therefore, the over voltage situations common in single stage topologies. The paper includes the operating principle and the design of the FWC in a high efficient bridgeless single stage converter. Experimental results to demonstrate the correct operation of the FWC are also presented.