Hermetic N-Channel HEXFET for High-Reliability Power Switching
The IRF225 is an N-Channel enhancement-mode power MOSFET built on the HEXFET structure, housed in a hermetic TO-3 package. It is rated for a drain-source voltage of 250 V, continuous drain current of 3.3 A, and power dissipation of 40 W. The hermetic TO-3 package seals the die against moisture and contamination, making this part suited for military, aerospace, and downhole environments where standard plastic-packaged MOSFETs would fail from corrosion or outgassing.
250 V / 3.3 A — Thermal and Load Budget
The 250 V drain-source rating provides headroom for a 170 VDC or 120 VAC rectified bus in motor drives, inverters, and switch-mode power supplies. The 3.3 A continuous current is the DC limit at case temperature; actual usable current derates with junction temperature per the datasheet's SOA curve. With a 40 W power dissipation ceiling, the thermal design must keep the case-to-ambient resistance low — a TO-3 bolted to a heatsink with thermal compound typically achieves 1–2 °C/W junction-to-case. Budget the heatsink area for the worst-case conduction loss at 3.3 A and the switching loss at the target frequency.
Through-Hole Mounting in the TO-3 Base
The through-hole mounting uses two 0.160-inch mounting holes on a 1.187-inch bolt circle, standard for TO-3. The collector (drain) tab is the case itself — the heatsink must be electrically isolated or the system ground must reference the drain potential.