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I have a SOT-23 SMD component marked \$\underset{\bullet}{\vert}3\bar{\textrm{S}}\;\bar{4}\$ as shown in the following images

Marking code pic 1

Marking code pic 2

I managed to find out that \$\textrm{3S}\$ stands for MMBT5551 NPN transistor. But I couldn't find the meaning of the prefix \$\underset{\bullet}{\vert}\$ and of the \$\bar{4}\$. I appreciate any help you can give me with it.

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  • \$\begingroup\$ BTW, +1 for the excellent markup \$\endgroup\$
    – Huisman
    Apr 19, 2019 at 12:19

1 Answer 1

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The bars on the top of the S and 4 mean "Non Lead-Free Marking".
Production year is 2005, week 4.

The dot of the \$\underset{\bullet}{\vert}\$ mark is the pin 1 marking (do check the datasheet, it has a pin numbering as well).

The combination of \$\underset{\bullet}{\vert}\$ means it was manufactured by a Philippine Subcontractor.

RoHS- Compliant Product Identification

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    \$\begingroup\$ I knew the bars had to do with RoHS-Compliance (non compiance in this case). That's the way how I found the linked document. \$\endgroup\$
    – Huisman
    Apr 19, 2019 at 11:58

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