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Based on a single-stage isolated power-factor-corrected power supply (SSIPP or S 2 IP 2) employing a boost powerfactor-correction (PFC) cell, the relationship between the input line voltage and line current of such switching regulators is studied. The conditions for unity power factor are derived. A control scheme to reduce the switch voltage stress while maintaining unity power factor is proposed. Practical implementation of the proposed control scheme is discussed. It is found that, by adding a simple input voltage feedforward to a conventional PWM controller, the switch voltage stress can be much reduced, while keeping the power factor very close to unity. Analysis and experimental results indicate that such a scheme is effective and feasible.

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