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Power-Factor-Slide14

In applications above 250 watts, Continuous Conduction Mode, or CCM, as it is called, is the preferred choice. In this mode, the switching frequency is fixed and regulation is achieved by varying the Ton to Toff ratio. Depending on the inductor value, the ripple current and peak MOSFET current is much lower for the same output power. At lighter loads, the PFC converter transitions to fixed frequency Discontinuous Conduction Mode (DCM) mode, which can deliver a lower switching frequency than critical conduction mode at light load and high line. However, the overall control concept is relatively complex. The greatest disadvantage of the CCM mode is that it requires hard commutation of the body diode and requires a low QRR specification to minimize MOSFET turn-on stress and losses. Zero QRR diodes like Silicon Carbide work best in this regard. Also, both turn-on and turn-off performance of the MOSFETs must be optimized as much as possible to get the best efficiency.

PTM Published on: 2011-09-02