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Power-Factor-Slide13

The boost converter can be designed and optimized for different modes of operation depending on the output power requirements. In the lower power ranges, operating in Critical Conduction Mode (CrCM) is favored for several reasons. While there is no gap in inductor excitation, the diode is never commutated with load current across it, so Qrr losses don’t occur. Additionally in critical conduction mode, Quasi zero voltage turn-on of the MOSFET is possible and turn on losses are near zero as load current is also zero. This relaxes the turn-on performance requirement for the MOSFET. Peak current limitation is inherent in this design due to the fundamental control mode. On the downside, the switching frequency is inversely proportional to the output load, so this is better for fixed load applications. At light load and high line, the switching frequency rises to a high value. Also, the peak switch current is always twice the average input current, which places higher stress on the MOSFET and the EMI filter.

PTM Published on: 2011-09-02