Surface-mount NPN small-signal bipolar junction transistor in a SOT-23 package, the SMD counterpart of the 2N3904. Rated for 40 V collector-emitter, 200 mA collector current, with a DC current gain of 100-300 at 10 mA and a 300 MHz transition frequency. Suited to general-purpose amplification and switching. Package marking is K1N.

Pinout

Pin	Name	Type	Function
1	B	input	Base terminal of the NPN BJT. Controls collector current via base drive; VBE(sat) = 0.65-0.95V at IC = 10-50mA. Emitter-Base breakdown voltage BVEBO = 6.0V.
2	E	passive	Emitter terminal of the NPN BJT. Typically tied to circuit common or emitter-degeneration network. Emitter-Base breakdown voltage BVEBO = 6.0V.
3	C	passive	Collector terminal of the NPN BJT. Collector-Emitter breakdown BVCEO = 40V, Collector-Base breakdown BVCBO = 60V, max collector current IC = 200mA.

Key specifications

Parameter	Value
Type	NPN small-signal BJT
Collector-emitter voltage (VCEO)	40 V
Collector-base voltage (VCBO)	60 V
Emitter-base voltage (VEBO)	6 V
Collector current (IC)	200 mA
DC current gain (hFE)	100-300 @ IC = 10 mA
Transition frequency (fT)	300 MHz
Package	SOT-23
Body (L×W×H)	2.9 × 1.3 × 1.1 mm

Ordering variants

Same part, different packaging or reel option.

MMBT3904-7-F
MMBT3904-13-F

CAD (KiCad official)

Symbol: Transistor_BJT:MMBT3904
Footprint: Package_TO_SOT_SMD:SOT-23
3D model: SOT-23 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Diodes Incorporated datasheet (7 pp, sha256 483284b10e2a58c8, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude) — every pin and dimension is cited to a datasheet page; refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF