PNDS / Marking codes / UD

Identify an unknown SMD part: marking code “UD”

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.

20 candidates 8 with manufacturer source-traceable

Candidate part numbers

Part number	Manufacturer	Package	Mapping source
2SC2821-D	TOS ^*	SOT-23 16ta - 3a Ren	Public marking directory
2SC3931-D	PANASONIC ^*	SC-70	Public marking directory
3SK127	TOS	SOT-143	Public marking directory
BCR151L3	INFINEON ^*	—	Public marking directory
BD45271G	ROHM ^*	SSOP-5	Public marking directory
R1114Q331D	RICOH ^*	SOT-143R	Public marking directory
SM4T18C	ST ^*	SOD-6	Public marking directory
US1D	GSI	DO-214AC	Public marking directory
2SC2404-D	—	SC-59	Public marking directory
2SC4627-D	—	SC-75	Public marking directory
FUES1D	—	DO-214AC	Public marking directory
KDS114	—	SOD-323	Public marking directory
KDS114E	—	SOD-523	Public marking directory
KDV175	—	SOD-323	Public marking directory
KDV175E	—	SOD-523	Public marking directory
P4SMAJ12C	—	DO-214AC	Public marking directory
R5323N024B	—	SOT-23-6	Public marking directory
XC6127C22JNR	—	SSOT-24	Public marking directory
XC6215B442NR	—	SSOT-24	Public marking directory
XC6223E23BNR-G	—	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”

UB U1 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.