800 V N-channel MOSFET in a fully isolated TO-220FP
Where the 800 V rating and 340 mΩ matter most
The 800 V Vdss rating gives the STF17N80K5 comfortable margin for universal-input flyback converters (typical bulk rail around 400 V) and PFC stages where the drain voltage can ring above the DC bus. The 340 mΩ Rds(on) at 10 V drive is a middle-ground figure — low enough to keep conduction losses reasonable in a 14 A part, but not so low that the gate charge penalty climbs. The 26 nC total gate charge means a small gate-drive transformer or a simple driver IC can switch it at 100 kHz without excessive drive losses.