The UCC24650 is an easy-to-use secondary-side voltage monitor that periodically measures
its own VDD voltage. A relative droop of 3% from the previous reading triggers a
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.
Relative-droop detection allows scaling to any voltage between 5 and 28 V. The
alert function allows very-low standby frequency to
minimize switching loss and reduction of output capacitance needed to respond to a heavy load step.
This monitor is used with a controller capable of detecting the signal, such as the UCC28730 PSR flyback controller.
The UCC24650 also provides an enable and disable signal which can be used to control a
secondary-side circuit during no-load conditions to reduce standby power loss. Such a circuit may
be a synchronous rectifier controller or a relay driver, for example.
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