800 V switching MOSFET in a thermally isolated package
The STF25N80K5: The 800 V drain-to-source rating suits flyback converters, PFC stages, and two-switch forward topologies. The 19.5 A continuous drain current is the package-limited figure in the TO-220FP full-pack isolation.
Gate drive and switching loss budget
The 5 V gate threshold at 100 µA drain current is the maximum — typical units turn on closer to 3–4 V, but the datasheet guarantees full enhancement only at 10 V drive.
The 150°C maximum junction temperature is the hard limit for the silicon — the TO-220FP package's thermal resistance will be the bottleneck in practice, so the 40 W dissipation rating assumes an infinite heatsink. In a real chassis mount, derate aggressively above 100°C case temperature.
That is the expected lifecycle for a mainstream SuperMESH5™ part — the series is current-generation technology, not a phase-out line.