Primary-Side PWM Controller Facilitates Off-Line Power-Ups

The UCC3809 primary-side PWM controller delivers excellent regulation and facilitates efficient off-line power-up while providing advanced protection features. The controller is intended for use in systems where a secondary-side error signal is already available. Using typical PWM controllers with an isolated optocoupler feedback, a 431-type shunt regulator provides the error signal, with the error amplifier typically programmed for unity gain. As a primary-side controller, the UCC3809 does not include an on-board error amplifier. This reduces IC costs in most settings.The device includes all other control and drive circuits required for off-line and isolated dc/dc fixed-frequency, current-mode switching supplies.