800 V N-channel in a fully isolated TO-220FP
The STF2N80K5 is an 800 V, 2 A N-channel MOSFET from ST's SuperMESH5™ series, built for off-line power conversion and auxiliary supply stages where high-voltage margin and low gate charge matter. The TO-220FP full-pack package isolates the back tab electrically, so you skip the mica washer and bushings when bolting to a chassis heatsink — one less assembly step and a lower thermal resistance path to ground.
The 3 nC typical gate charge at 10 V keeps the driver stage small; a 100 mA gate-drive source charges it in 30 ns, which suits flyback converters switching in the 65–100 kHz range. Input capacitance is 95 pF at 100 V drain-source, so the switching node rings less than with higher-Ciss parts, and the driver sees a light capacitive load. The 5 V maximum gate threshold at 100 µA drain means logic-level drive (5 V logic) will barely turn it on — plan for a 10 V gate rail to get the rated Rds(on).
The TO-220FP package is a through-hole, fully moulded case — no exposed metal tab, so the mounting screw does not need an insulating shoulder washer. Power dissipation is 20 W at case temperature; derate above 25 °C per the datasheet curve.