Obsolete — plan your BOM move now
The STMicroelectronics TIP122FP is an NPN Darlington transistor in the TO-220-3 Full Pack (TO-220FP) package, rated for 100 V collector-emitter breakdown and 5 A continuous collector current. It offers a minimum DC current gain of 1000 at 3 A collector current and 3 V Vce, with a saturation voltage of 4 V max at 20 mA base drive and 5 A collector current. The junction temperature limit is 150°C, and the package dissipates up to 2 W. This part is officially listed as Obsolete by STMicroelectronics.
The 100 V Vce(max) and 5 A Ic(max) define the safe operating area for switching inductive loads like relays, solenoids, motors, and lamp drivers. The 4 V saturation voltage at 5 A means the on-state power dissipation is significant — at full current, expect roughly 20 W of conduction loss, which exceeds the 2 W package limit. In practice, this part is used for medium-current switching with adequate heatsinking or pulsed duty cycles where average dissipation stays under 2 W. The minimum hFE of 1000 at 3 A means a microcontroller pin can drive it directly through a series base resistor — a 5 V logic output sourcing 5 mA can switch up to 5 A of collector current. That high gain is the Darlington pair's advantage over a single BJT.
TO-220FP full-pack — no heatsink tab isolation worries
The TO-220-3 Full Pack (TO-220FP) is a fully isolated package — the metal tab is encapsulated, so no insulating washer or pad is needed when bolting it to a chassis or heatsink. The 2 W power rating is for the package without an external heatsink; with a proper heatsink and thermal compound, the effective dissipation can increase, but the junction temperature must stay under 150°C. The through-hole mounting suits point-to-point wiring, perfboard, or PCB layouts with 0.1-inch pitch.