40 V, 200 mA NPN in SOT-23 — the workhorse small-signal switch
The STMicroelectronics MMBT3904 is a general-purpose NPN transistor in the industry-standard SOT-23-3 package, rated for 40 V collector-emitter breakdown and 200 mA continuous collector current. With a 350 mW power dissipation limit and a 270 MHz transition frequency, it handles low-frequency switching and linear amplification in control logic, sensor interfaces, and signal conditioning stages on a mixed-signal board.
Parametric floor for the BOM line
Vce saturation is 200 mV max at Ib=5 mA, Ic=50 mA — the voltage drop across the collector-emitter junction stays low enough that the transistor does not steal headroom from the load in a saturated switch application. Junction temperature rating of 150 °C (TJ) means the die can tolerate brief thermal spikes during reflow or in a warm enclosure, but the 350 mW power limit governs steady-state operation — derate above 25 °C ambient per the datasheet curve.
Obsolete — plan the last-time-buy or cross-reference
STMicroelectronics lists the MMBT3904 as Obsolete. No official successor order code is recorded in the lifecycle data. The part is RoHS Compliant per, so any remaining stock or surplus lots carry the current environmental compliance — no end-of-life exemption expiry to track. For a BOM that still calls out this exact order code, sourcing runs through independent distribution and surplus channels. Availability and pricing are confirmed at RFQ time against the required quantity.
SOT-23-3 footprint and reel handling
The MMBT3904 ships in the SOT-23-3 package (TO-236-3 / SC-59 equivalent), a 3-lead surface-mount package with a 0.95 mm lead pitch and a 2.9 mm body width — standard for pick-and-place and reflow assembly. Available in Tape & Reel (TR) or Cut Tape (CT) formats. The reel quantity is not specified in the listing; confirm the reel count with the supplier at quote time. Store the reels in a dry environment — SOT-23 devices are not moisture-sensitive by default, but the carrier tape can absorb humidity in long-term storage.