620 V N-Channel MOSFET — the flyback primary switch
The STMicroelectronics STF3N62K3 is a 620 V N-channel power MOSFET from the SuperMESH3™ family, built with a metal-oxide gate structure. It is designed for offline flyback converters, PFC stages, and auxiliary power supplies where the primary switch sees a reflected voltage plus a safety margin.
Gate charge and switching — 13 nC keeps the driver happy
Input capacitance measures 385 pF at 25 V drain-source.
TO-220FP full pack — no insulating washer needed
The through-hole TO-220FP package has a fully molded plastic body with no exposed metal tab. That means the heatsink interface does not require an insulating pad or mica washer — the back of the package is already isolated. The trade-off is higher thermal resistance than a standard TO-220 with a metal tab; the 20 W maximum dissipation at the case assumes a good thermal bond to a heatsink. If the board runs in a confined enclosure, budget for a clip-on heatsink or a larger pad area on the PCB.
Active lifecycle — no LTB concern for production
ST lists the STF3N62K3 as Active.