We are using the UCC3817AD in a PFC with Vac range from 80-264V. At max rated load (130W in) the AC line current breaks up into chaotic noise with an extreme amplitude of ripple (roughly 17 - 20KHz). This noise starts near the crest of the Vac and continues down to the zero crossing where it becomes clean until the next crest of the rectified Vac. We have verified that it is not the pin 2 cycle-cycle current limiting. Any ideas what could be causing this?
A low bandwidth compensated Current Amplifier can clean it up but then has poor line current harmonics (15th and 21st triplens) because the current can't keep up with the fast cusp of the rectified Vac.
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