500 V N-channel in the TO-220 footprint
The STP14NM50N is a 500 V, 12 A N-channel power MOSFET from ST's MDmesh™ II series, housed in the through-hole TO-220 package. It is a discrete switch for medium-voltage power conversion — think flyback and forward converters, PFC stages, and offline switch-mode power supplies up to about 150 W.
Rds(on) at operating temperature is the real number
The datasheet lists 320 mOhm maximum Rds(on) at 6 A, 10 V gate drive, but that's the 25 °C junction figure. At 125 °C junction — the realistic operating point in a TO-220 dissipating 90 W — the on-resistance roughly doubles. Budget 600 mOhm hot Rds(on) for the conduction loss calculation. Gate charge is 27 nC at 10 V. That is modest — a standard 1 A gate driver switches it in under 30 ns. The input capacitance of 816 pF at 50 V drain-source is low enough that the driver sees a manageable reactive load, but the Miller plateau still governs the switching transition time. Plan for a 10 V gate rail to hit the rated Rds(on); a 12 V rail gives margin for threshold variation across temperature.