The STP3NK90ZFP is an N-channel MOSFET from ST's SuperMESH series, built for offline power supplies, flyback converters, and industrial auxiliary supplies where the DC bus sits at 380 V or higher. The 900 V drain-source rating gives you a solid 2× derating margin on a typical 400 V rail, which matters when the line rings during a surge.
Conduction and switching costs
Rds(on) is 4.8 Ohms maximum at 1.5 A with 10 V gate drive. That is not a low-Rds(on) part — it is a high-voltage device where the die is sized for breakdown, not for minimal resistance.
The TO-220 Full Pack package (TO-220FP) has a fully isolated metal tab — no extra insulating washer needed, which speeds up assembly and reduces thermal interface variability. The through-hole mounting suits point-to-point wiring on prototype boards and production runs where vibration resistance matters.
The base product number is STP3NK90, and the 'Z' suffix designates the SuperMESH generation.