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Critical conduction mode boost power factor correction converters operating at the boundary of continuous conduction mode and discontinuous conduction mode have been widely used for power applications lower than 300W. This paper proposes an enhanced variable on-time control method for the critical conduction mode boost PFC converter to improve the total harmonic distortion characteristic. The inductor current, which varies according to the input voltage, is analyzed in detail and the optimal on-time is obtained to minimize the total harmonic distortion with a digital controller using a TMS320F28335. The switch on-time varies according to the input voltage based on the computed optimal on-time. The performance of the proposed control method is verified by a 100W PFC converter. It is shown that the optimized on-time reduces the total harmonic distortion about 52% (from 10.48% to 5.5%) at 220V when compared to the variable on-time control method.

A new half bridge converter with parallel-series connected four-transformer is proposed for an electric vehicle charger with wide range zero voltage switching operation. The proposed converter combines two sets of two-transformer half bridge converter as a parallel-series connection to accommodate an auxiliary battery charger in an automotive application. The circuit configuration and principles of operation are analyzed in detail and design equations are presented. To verify advantages of the proposed converter, 1.2 kW hardware prototype is built.

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