PNDS / Marking codes / U1

Identify an unknown SMD part: marking code “U1”

Packages rarely print the full part number. The marking below is shared by several part numbers — use the package, pin count and the manufacturer family together to narrow it down, then confirm against the datasheet.

17 candidates 9 with manufacturer source-traceable

Candidate part numbers

Part number	Manufacturer	Package	Mapping source
3SK283	TOS	SOT-143	Public marking directory
BCX19	FSC	SOT-23	Public marking directory
BD45391G	ROHM ^*	SSOP-5	Public marking directory
BGX50A	INFINEON	SOT143	Public marking directory
MMSZ3V9	ON ^*	SOD-123	Public marking directory
R3111Q111C	RICOH ^*	SC-82AB	Public marking directory
R3116Q381C	RICOH ^*	SC-82AB	Public marking directory
RN2102FS	TOS	—	Public marking directory
TC74A1-5.0VCT	TOS ^*	SOT-23-5	Public marking directory
ELM7621LCB	—	SOT-23 16vdc VD7 3d Elm	Public marking directory
FES1A	—	DO-214AC	Public marking directory
R1131D311D	—	—	Public marking directory
R1163D311B	—	—	Public marking directory
R5323N032B	—	SOT-23-6	Public marking directory
RP104Q211C	—	SC-82AB	Public marking directory
UDZ56B	—	SOD-323	Public marking directory
XC6215B322NR	—	SSOT-24	Public marking directory

How we narrow this down

Package first — SOT-23 vs SOD-123 vs SC-59 eliminates most candidates immediately.
Pin count and body size — a 3-pin SOT-23 LDO cannot be a 6-pin dual transistor.
Marking style — laser-marked parts are usually newer production; ink marking often indicates older or second-source vendors.
Circuits around it — a part sitting on a rail with an inductor is a regulator, not a diode.
Datasheet check — every credible candidate lists its marking scheme in the “marking information” section.

FAQ

Same code, several parts — which one do I actually have? Compare package + pin count + surrounding circuit; if it still fits two parts, request a sample verification before production.
Can I substitute between the candidates? No — the same marking may sit on electrically different parts. Always match the electrical spec sheet, not just the marking.
Where do these mappings come from? Public SMD marking directories and historical stock tables; each row keeps its source so you can trace it.

Other codes starting with “U”

UD UB U2 U3 U4 U6 UC UE UF U5

Still not sure what the part is?

Send the code, package and a photo through the BOM hub — our engineers cross-check it against datasheets and sourcing records.

How these mappings are compiled: public SMD marking directories plus our own stock records. Each row keeps its original reference internally, so any mapping can be traced on request. ^* Manufacturer derived from the part-number family (some directory entries carry no manufacturer) — treat it as a lead, not a datasheet fact. Markings are indicative only — confirm with the physical batch marking and the original datasheet before ordering.