I found this circuit in a schematic I'm reviewing, which supposedly provides a regulated +5 V supply. The primary side of the transformer includes a flyback controller that switches ~340 VDC on the primary coil. The secondary coil is labeled as '5V @ 0.1A.'
What kind of IC is U1? At first I thought it was some sort of in-rush current limiter given the large amount of bulk capacitance (C2 – C10) but I don't see a way of the IC measuring current. Maybe an ideal diode? The 'TON' and 'TOFF' labels throw me off, though.
Not shown: the +5 V is fed back to the primary-side controller via an optoisolator and bias circuitry (voltage reference and some passives). This circuitry can be provided but does not seem relevant to the question.
(Also, apologies for the sub-par schematic layout. I only have access to the PDF, else I would have laid it out so that it's easier to read.)
Best Answer
Probably a Synchronous Rectifier Controller chip.
For example, the UCC24610 (which appears to match your pinout).
The chip controls the MOSFET gate so it acts as a more efficient rectifier than a Schottky diode would be.