Hermetic N-channel HEXFET in a TO-3 can
The IRF323 is an N-channel hermetic MOS HEXFET designed for high-voltage switching in military, aerospace, and industrial power systems where the TO-3 package's metal can provides a sealed environment and a low-thermal-resistance path to the heatsink. Rated for 350 V drain-source and 2.8 A continuous drain current.
50 W power dissipation — the thermal budget anchor
For a 2.8 A load at 350 V bus, the conduction loss (Id² × Rds(on)) must stay under this ceiling; a 1.5 A load at 50 % duty cycle leaves about 20 W margin for switching losses in a hard-switched converter. The TO-3 package's metal baseplate conducts heat directly to the chassis or heatsink — no plastic interface. The mounting screw torque and thermal compound application directly set the junction-to-case thermal resistance; a dry joint or under-torqued screw can cut the usable Pd by half.
Active status does not guarantee infinite availability; the hermetic TO-3 market has consolidated over the years. Sourcing through independent distribution provides a secondary channel that can cover allocation gaps or end-of-life transitions when they eventually come.