Texas Instruments' UCC24650 is an easy-to-use, secondary-side voltage monitor that periodically measures its own V_DD voltage. A relative droop of 3% from the previous reading triggers an alert signal to a receiving primary-side regulation (PSR) controller. Its low-power consumption helps achieve <5 mW standby loss in many applications.

An internal 200 V MOSFET switch is applied across a ground-referenced rectifier to provide a current-limited pulse to the flyback transformer secondary winding, which couples the signal to the primary-side controller. This signal is repeated at 33 kHz until controller-driven switching activity is detected.