SLUSD37E October 2017 – November 2019 UCC28056
The input rectifier and capacitor form an analog peak detector that accumulates the peak Line voltage applied to the input. This peak Line voltage appears across the Boost MOSFET. The controller observes peak Line voltage via the external divider network attached to the ZCD/CS pin. The Line voltage start comparator does not allow the controller to exit the Stopb state until the ZCD/CS pin voltage rises above the VZCBoRise threshold. This behavior ensures that switching operation does not start until the Line voltage is high enough (85 VRMS) to deliver full output power. During switching operation, the controller continues to operate regardless of the Line voltage, until a fault causes it to enter a Stopb state.