NPN Darlington — 60 V, 5 A, TO-220
The STMicroelectronics TIP120 is an NPN Darlington transistor in a TO-220-3 through-hole package, rated for 60 V collector-emitter breakdown and 5 A continuous collector current. The Darlington pair gives a minimum DC current gain (hFE) of 1000 at 3 A, 3 V — so a microcontroller pin driving 20 mA into the base can switch a 5 A load without a second driver stage.
Gain and saturation — what the numbers mean for the circuit
Vce saturation is specified at 4 V maximum with 20 mA base current and 5 A collector current. That 4 V drop at 5 A means 20 W dissipation during saturation — well above the 2 W package limit — so the transistor must be switched fully on or off, not operated in the linear region at high current. The 1000× minimum gain at 3 A means a base drive of only 3 mA saturates the output at that current, keeping the base-drive circuit simple. The 500 µA maximum collector cutoff current at 150°C junction temperature sets the off-state leakage floor. In a high-impedance load, that leakage can bias the next stage; a pull-down resistor on the output is worth budgeting.
TO-220 package — mounting and thermal path
The TO-220-3 package (supplier device package TO-220) is a through-hole tabbed package. The metal tab is the collector — it must be electrically isolated or connected to the collector rail. For any continuous current above a few hundred milliamps, the tab should be bolted to a heatsink; the 2 W maximum power assumes adequate heatsinking. The junction temperature limit is 150°C.
Lifecycle and sourcing — obsolete, ROHS3 compliant
The TIP120 is classified as Obsolete by STMicroelectronics. It remains ROHS3 compliant. Sourcing is through independent distribution — quoted to order against the BOM quantity; availability and current pricing confirmed at RFQ.