45 V, 500 mA — the switching ceiling
The BCW71 is an NPN transistor rated for 45 V collector-emitter breakdown and 500 mA continuous collector current. That combination covers low-side switching for relays, solenoids, and indicator loads in 12 V and 24 V industrial logic circuits, where the 45 V Vce gives margin above the rail for inductive flyback.
330 MHz ft — bandwidth for signal conditioning
A transition frequency of 330 MHz makes the BCW71 usable as a preamplifier or buffer up into the VHF band. For a common-emitter stage with a gain of 10, the closed-loop bandwidth lands around 33 MHz — enough for video line drivers, RF envelope detectors, or high-speed comparator front-ends. The 250 mV saturation voltage at 500 µA base, 10 mA collector keeps conduction losses low in saturated switching — the transistor drops under 0.25 V when fully on, which matters for 3.3 V logic where every millivolt of headroom counts.
SOT-23-3 — footprint and thermal budget
Housed in the industry-standard SOT-23-3 package (TO-236-3 / SC-59 variant), the BCW71 shares the same 2.9 mm × 1.3 mm footprint as thousands of other small-signal transistors. Surface-mount assembly with Tape & Reel or Cut Tape packaging; the SOT-23-3 lands on a standard 0.95 mm pitch pad layout and reflows with any lead-free profile that peaks below 260 °C.
No pin-compatible second-source is published by onsemi, but the SOT-23-3 footprint accepts many functionally equivalent NPN types if a cross-reference is needed.