800 V N-channel SuperMESH™ MOSFET in the TO-220FP isolated package
The STMicroelectronics STF12NK80Z is an 800 V N-channel power MOSFET from the SuperMESH™ series, built with a strip-layout vertical DMOS process that delivers a favorable figure of merit between on-resistance and gate charge. It is designed for high-voltage switching applications such as offline flyback converters, power-factor-correction (PFC) stages, and auxiliary power supplies where 800 V breakdown margin is needed to handle reflected voltage and line surges.
Rds(on) at junction temperature — the real loss number
That figure is at 25°C junction temperature. At a typical operating junction of 125°C, the on-resistance roughly doubles — expect around 1.5 Ω. This matters for the conduction-loss line item in the SMPS loss budget: the 750 mΩ headline is the starting point, not the design value.
For a typical 100 kHz hard-switched flyback, the gate-drive power requirement is roughly Qg × Vgs × fsw = 87 nC × 10 V × 100 kHz ≈ 87 mW — comfortable for a standard MOSFET driver IC but worth checking if the driver is a low-current auxiliary winding supply. The gate threshold voltage (Vgs(th)) has a maximum of 4.5 V at 100 µA, which means the device starts to turn on near 3–4 V; ensure the gate-drive pull-down holds the gate below 3 V during off-time to avoid shoot-through or partial conduction.
Thermal derating and the TO-220FP package
The continuous drain current rating of 10.5 A at 25°C case derates with temperature. The through-hole mounting (TO-220-3) is straightforward for hand-assembly or wave-solder production.
For BOM continuity, the base product number STF12 covers the family; the suffix encodes the voltage and current grade.