1200 V N-channel — the high-voltage workhorse
The STP8N120K5 is a 1200 V N-channel power MOSFET from ST's MDmesh™ K5 series, designed for high-voltage switching applications where conduction losses and switching speed both matter. The 13.7 nC typical gate charge keeps the driver stage light, which matters when you're pushing the switching frequency above 50 kHz in a flyback or PFC stage.
The 1200 V Vdss is the headline: this part lives in offline converters where the bulk rail can hit 800 V in a universal-input power supply, leaving 400 V of margin for ringing and transients. The 2 Ohm Rds(on) at 10 V gate drive sets the conduction loss at 2.5 A — roughly 12.5 W at full current, which the 130 W package dissipation can handle with a decent heatsink. The 13.7 nC gate charge means a standard gate driver IC can switch it without excessive cross-conduction; compare that to older 1200 V planar MOSFETs that often needed 30–40 nC.
No last-time-buy clock is ticking.