Design Support

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When a PFC is in discontinuous conduction mode, the inductor current will resonant between the boost inductor and MOSFET parasite capacitance. The resonant current can be big enough to distort the PFC current significantly. This application note introduces a digital control scheme based on UCD3XXX to predict the position at which the resonant current first time rises back from negative to zero, and turning on the MOSFET at this position to minimize PFC current distortion. Since the switch node is either zero voltage or valley voltage at this position, the efficiency is also improved.