I have several transistors, I understand that the last digits on the first line define what the transistor is.

There's a second code as well. I've added some photos. What does this code mean?

image of C1815 CR331 A42 B331 2N3904 H341


2 Answers 2


The numeric part is probably a date code.

The part before that is useful- it is the beta bin which indicates a range for hFE.

For example, for the Japanese 2SC1815:

hFE VCE=6.0V, IC=2.0mA (2SC1815) 70 700
hFE VCE=6.0V, IC=2.0mA (2SC1815-O) 70 140
hFE VCE=6.0V, IC=2.0mA (2SC1815-Y) 120 240
hFE VCE=6.0V, IC=2.0mA (2SC1815-GR) 200 400
hFE VCE=6.0V, IC=2.0mA (2SC1815-BL) 350 700 

The one you have has an hFE between 200 and 400 with Vce = 6V and Ic = 2mA.

Having a relatively narrow 2:1 range for hFE can allow more optimized designs, especially for non-trivial analog circuits, such as amplifiers and RF circuits.

You will probably find similar codes on the datasheets for the MPSA42 and the 2N3904. Also note that I'm supplying a missing prefix on two of the three transistors.

  • \$\begingroup\$ +1. Ah yes. Completely forgot about binning info. \$\endgroup\$ Jun 7, 2018 at 19:16
  • \$\begingroup\$ I've seen hFE written in places. I didn't know what it meant. I think some more reading is in order. \$\endgroup\$
    – BanksySan
    Jun 7, 2018 at 19:30

Generally it is manufacturer specific.

Usually it will be something like a:

  • Production Lot Number
  • Date Code
  • Binning Information (device performance characteristics)
  • Revision Number
  • Fab/Foundry Identifier
  • Packaging Info (e.g. RoHS, Pb Free, etc.)

Or it could be a mixture of more than one of those things.

There are also cases where the "bottom line" is the part number, and the "top line" is the extra info.

The number of lines isn't limited to just two either (as seen in the third image now I come to think of it).

  • \$\begingroup\$ Are they something I need to consider when I get a datasheet or is the first code the important bit? \$\endgroup\$
    – BanksySan
    Jun 7, 2018 at 19:02
  • \$\begingroup\$ Interesting that three different transistors have such similar "bottom lines." There's the number 331 on all of them, and either H or B. \$\endgroup\$
    – JRE
    Jun 7, 2018 at 19:04
  • \$\begingroup\$ @BanksySan maybe. I can't really be more specific. There's no hard and fast rule. Generally probably not. \$\endgroup\$ Jun 7, 2018 at 19:05
  • \$\begingroup\$ @TomCarpenter I'll assume not unless I find otherwise then. Thanks. \$\endgroup\$
    – BanksySan
    Jun 7, 2018 at 19:09
  • \$\begingroup\$ @JRE Aye, they all have 331. B, GR, C, D, P, H, A or CR. \$\endgroup\$
    – BanksySan
    Jun 7, 2018 at 19:11

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