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2022-09-24 23:33:15
UCC2858DW - Power Factor Controller
The UCC3858 provides all the necessary control functions for active power factor correction preregulators requiring high efficiency low power operation. A nearby power factor controller implementation shapes the AC input current waveform to correspond to the line voltage of the AC input using average current mode control. The operation of the UCC3858 is very similar to the previous design of Unitrode's PFC section with additional features that allow higher efficiency to improve converter operation at light loads. This is achieved by linearly scaling down the PWM frequency when the output voltage of the error amplifier drops below a predetermined user-programmable indicated level at light load conditions. Reduced CT ramp (proportional output power) for frequency scaling charge current and increased dead time. There is also a momentary reset input that pulls the IC into foldback mode very quickly when the load comes back. Leading edge modulation of UCC3858 PWM technology. When combined with a more conventional trailing-edge modulation downconverter, this scheme provides the benefit of lower ripple current on the bulk storage capacitor. The oscillator is designed for easy synchronization to downstream converters. A simple synchronization scheme can be implemented by connecting the PWM output to the SYNC pin of the downconverter.