800 V N-channel in a full-pack TO-220
The STF15N80K5 is an 800 V, 14 A N-channel power MOSFET from ST's SuperMESH5™ series, built on a strip-layout vertical DMOS process that targets low gate charge and fast switching in offline power supplies.
375 mOhm on-resistance — conduction loss anchor
That 10 V drive level is the design target — the part is optimised for a Vgs of 10 V, not 5 V logic-level drive. At 7 A the conduction loss works out to about 18 W, which sits within the 35 W power dissipation rating at the case, but the junction-to-case thermal resistance of the full-pack package means the heatsink selection is the real limiter.
Gate charge and input capacitance — switching speed budget
For a 100 kHz hard-switched flyback, the gate drive needs to source about 3.2 mA average current — a standard PWM controller's totem-pole output handles that without an external driver. The 1100 pF Ciss also sets the Miller plateau duration; expect a few tens of nanoseconds of plateau time, which keeps the switching loss reasonable in a QR or active-clamp topology.
Temperature envelope and threshold voltage
The maximum gate threshold voltage is 5 V at 100 µA drain current — a 10 V drive ensures the FET is fully enhanced across the full temperature range, because Vgs(th) drops roughly 4 mV/°C as the junction heats. At 150°C junction, a 5 V gate signal may not keep the device in the ohmic region; the 10 V drive voltage eliminates that risk.