The LT®1509 is a complete solution for universal off-line switching power supplies utilising active power factor correction. The PFC section is identical to the LT1248 PFC controller except the EN/SYNC pin is removed because PFC and PWM are synchronized internally. The current mode PWM section (the LT1508 is the volt-age-mode counterpart) contains all the primary side functions to convert the PFC preregulated high voltage output to an isolated low voltage output. The PWM duty cycle is internally limited to 47% (maximum 50%) to prevent transformer saturation. PWM soft start begins when PFC output reaches the preset voltage. In the event of brief line loss,the PWM will be shut off when the PFC output voltage drops below 73% of the preset value.
