SOT-23 marking codes

Identifying a part in SOT-23

SOT-23 is the three-lead plastic body about 2.9 by 1.3 mm. JEDEC calls it TO-236AB, SC-59 (SOT-346) is a near-identical outline, and ROHM names it SMT3. The five- and six-lead SOT-23-5 and SOT-23-6 are packages of their own, listed separately.

One body holds bipolar transistors, MOSFETs, single and dual diodes, Zeners and voltage references, so the code alone rarely settles what a part is. The diode range narrows it: a MOSFET shows a body diode between drain and source and an open gate, while a transistor and a diode pair with a common pin both read two junctions from one pin, which only the pinout or the circuit separates.