The STMicroelectronics STFI9N80K5 is an N-channel MOSFET from the MDmesh™ series, designed for high-voltage switching applications such as power supplies, adapters, and lighting ballasts. The STFI9N80K5 is listed as obsolete. For existing BOM lines, sourcing is limited to the surplus and broker market.
The 800 V Vdss rating gives you headroom for universal-input AC-DC converters (up to 400 VDC bus) and flyback topologies with reflected voltage spikes. The 12 nC gate charge is low, which keeps switching losses manageable and simplifies the gate drive circuit — a standard 10 V supply can drive it without a dedicated booster. Input capacitance is 340 pF at 100 V drain-source, so the driver sees a light capacitive load. The ±30 V maximum gate-source voltage gives good margin against overshoot on the gate node. The 5 V gate threshold maximum at 100 µA drain current means the device is fully enhanced with a 10 V drive, but it will not turn on cleanly with 5 V logic — you need a 10 V rail or a gate driver that swings to 10 V.
Package and mounting — through-hole I2PAKFP
The supplier device package is I2PAKFP (TO-281). The three through-hole leads are sized for standard 1.6 mm PCB holes. The full-pack construction means the metal tab is electrically isolated from the drain, simplifying assembly and reducing creepage concerns in high-voltage designs.