Hi Power Group,
What parameters set the upper switch frequency of a Transitional Mode PFC or Single Stage Flyback PFC?
Normally I see switch frequencies in the 100K range. Can the PFC inductor or Flyback transformer size be reduced by operating at higher frequencies say in the 250K to 500K range?
Regards,
Stuart Linzer
Hi Stuart,
For Transition Mode, TM (or sometimes referred to as Critical Conduction Mode, CrM) PFC, the frequency will vary depending on the difference between Vin and Vout and also where you are within the input line cycle.
The maximum frequency is limited by the minimum on time of the controller as well as the demag time of the inductor. For the UCC28064A, on time can be reduced by increasing RT (thereby contributing to a higher frequency) . From the -064A datasheet:
However, as with most of engineering, there's no free lunch. You need to be mindful balancing peak currents and power delivery capability (and EMI) as you increase the frequency and reduce the inductor value.
Regards,
Ray
