TIP120 NPN Power Darlington Transistor (TO-220)

A single small-signal transistor like the BC547 can only switch milliamps directly from a microcontroller pin, which falls far short of what a real motor or high-current relay coil needs. The TIP120 solves this by internally combining two transistors into a Darlington pair, multiplying the current gain so a weak microcontroller signal on its base pin can still switch several amps on its collector, all without needing a separate driver transistor stage in between. That makes it a practical, low-parts-count way to switch DC motors, solenoids, heating elements, and other higher-current loads directly from a digital logic pin, in the gap between a tiny signal transistor and a full power MOSFET.