UCC38500DW..

IC, PFC/PWM CONTROLLER 20-SOIC.

The UCC38500DW is a BiCMOS PFC/PWM Combination Controller provides all of the control functions necessary for an active power-factor-corrected pre-regulator and a second-stage DC to DC converter. 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 DC to DC converter uses peak current-mode control to perform the step-down power conversion. The PFC stage is leading-edge modulated while the second stage is trailing-edge synchronized to allow for minimum overlap between the boost and PWM switches. This reduces ripple current in the bulk-output capacitor. In order to operate with over three-to-one range of input-line voltages, a line feed-forward (VFF) is used to keep input power constant with varying input voltage. Generation of VFF is accomplished using IAC in conjunction with an external single-pole filter.