High Efficiency, High Power Factor Preregulator

The UCC3858 provides all of the control functions necessary for active power factor corrected preregulators which require high efficiency at low power operation. The controller achieves near unity power factor by shaping the AC input line current waveform to correspond to the AC input line voltage using average current mode control. The operation of the UCC3858 closely resembles that of previously de- signed Unitrode PFC parts with additional features to allow higher effi- ciency boost converter operation at light loads. This is accomplished by linearly scaling back the PWM frequency when the output of the voltage error Amplifier drops below a predetermined user programmable level in- dicating a light load condition. The frequency is scaled back by reducing the charging current for the CT ramp (in proportion to the output power), and increasing the dead time. There is also an instantaneous reset input to pull the IC out of foldback mode quickly when the load comes back up. The PWM technique used in the UCC3858 is leading edge modulation. When combined with the more conventional trailing edge modulation on the downstream converter, this scheme offers the benefit of reduced rip- ple current on the bulk storage capacitor. The Oscillator is designed for easy synchronization to the downstream converter. A simple synchroni- zation scheme CAN be implemented by connecting the PWM output of the downstream converter to the SYNC pin. By Texas Instruments
UCC1858 's PackagesUCC1858 's pdf datasheet

UCC1858 Pinout, Pinouts
UCC1858 pinout,Pin out
This is one package pinout of UCC1858,If you need more pinouts please download UCC1858's pdf datasheet.

UCC1858 Application circuits
UCC1858 circuits
This is one application circuit of UCC1858,If you need more circuits,please download UCC1858's pdf datasheet.

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