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Power-Factor-Slide16

The control function for the boost converter shows the relationship between Vout and Vin with respect to the duty cycle. Keep in mind that while the voltage regulation loop senses the output voltage and is normally crossed over below 10 Hz, a separate current control loop varies the duty cycle following the AC input waveform. So for traditional architecture controllers, input voltage and input current sensing is required. A multiplier is used in the IC to program the MOSFET duty cycle to draw current in a resistive fashion as a function of the input voltage, this will occur even if the input voltage is not a clean sinusoid. In principle, the MOSFET VDS rating must be at least equal to the output voltage. However, in practice due to switching di/dt and stray inductance in the power circuits overshoots will occur typically as much as 15% above V-out. So MOSFET ratings of 600V are often advised for higher power PFC applications or where component de-rating is desired.

PTM Published on: 2011-09-02