PNDS / Marking codes / 51

Identify an unknown SMD part: marking code “51”

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.

25 candidates 8 with manufacturer source-traceable

Candidate part numbers

Part number	Manufacturer	Package	Mapping source
BAT15-115R	INFINEON	SOT173	Public marking directory
BAT15-115S	INFINEON	SOT173	Public marking directory
BAV199	DIODES	—	Public marking directory
CMZ51	TOS	—	Public marking directory
P6SMBJ51	LITTLE ^*	DO-214AA	Public marking directory
R3111Q511B	RICOH ^*	SC-82AB	Public marking directory
RN5RF51AA	RICOH ^*	SOT-23-5	Public marking directory
RN5RZ51AA	RICOH ^*	SOT-23-5	Public marking directory
CHDTC114YMPT	—	SOT-723 18ta - 3a Chm	Public marking directory
ELM9851BB	—	SOT-23 16cg VR1 3d Elm	Public marking directory
GLZ51	—	SOD-80	Public marking directory
Gali-51	—	SOT-89	Public marking directory
HMSZ5251B	—	SOD-323	Public marking directory
HZC5.1	—	SOD-523	Public marking directory
HZU5.1G	—	SOD-323	Public marking directory
KDZ5.1EV	—	SOD-523	Public marking directory
KDZ5.1V	—	SOD-323	Public marking directory
MAZY510	—	NMiniP2	Public marking directory
R1223N322F	—	SOT-23-5	Public marking directory
SML4757	—	DO-214	Public marking directory
TCMM5Z2V7	—	SOD-523	Public marking directory
U1Z51	—	SOD-6	Public marking directory
U1ZB51	—	I-FLAT	Public marking directory
XC6221D391NR	—	SSOT-24	Public marking directory
ZD5251BS2	—	SOD-323	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 “5”

5A 5B 5C 5D 52 5H 55 56 5E 5F

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.