# Help understanding “unusually talked about” transistor code markings

I am a beginner trying to gain a better understanding of transistor codes. Before posting this, I searched the web looking for answers but I was unsuccessful.

Please take a moment to look at the transistors picture below:

Here are my questions:

1. Unless I am wrong, all of the transistors on the picture are supposed to represent the 2222 transistor. If this is the case, then why aren’t all those transistors specs identical? Isn't the 2222 supposed to exactly define the transistor properties construction, behavior etc? If yes, shouldn’t all have identical properties?

2. All of the transistor have a suffix. The first one has “A338”, the second “F42” and the third “B25”. What do those values stand for? If they are specified on the spec sheet could someone please point out to me where because I was not able to find them.

3. You will notice that the second transistor has a dot or dash before the “F42” and that the third transistor has a dot at the beginning and one at the end of its code. What do those dots / dashes represent?

4. The third transistor is specially weird (at least to me) because it seems to combine values that the other two do not. Specifically, its first line has the text "P2N2" when I would have have expected to only see the "P2N” text and on the second line the text "2222A". I am assuming they did this due to lack of space which makes me wonder if the dots around the text signify that the code should be read as a single line and not as a multiline?

1. The trasistor's complete identifier is not just 2222 but 2N2222A.
The A may be not unimportant depending on the application. It tells about ranges of the $h_{FE}$, $f_T$ and others parameters.
The 2N prefix is sometimes omitted because it is used only for transistors (another prefix 1N is used only for diodes as you may know from the famous 1N4148 diode) and it is assumed that is is clear that the device is a transistor.
BTW "spec" is not the right term. By "spec" I would rather understand the datasheet.

2.   3. and 4.: All the other characters have no general meaning.
I.e. it depends on the manufacturer what they are used for. They may indicate the manufacturing batch oder the date/week of manufacturing etc.

The markings on semiconductors are meaningless. They depend entirely on the manufacturer and their particular nomenclature. The fact that these transistors can even be identified at all is uncommon. Many components can't be identified from the markings at all. There is a chance that the nomenclature is listed in the components data sheet but it may not be.

The only way to compare components is from the manufacturers data sheets.

• I'd disagree that they are meaningless; they are very meaningful within the scope of that manufacturer. But the meaning is often hard to trace as the markings are rarely publically explained and if they are, it is only somewhere in a footnote in the datasheets. That being said, I have certainly reverse engineered entire random chinese PCBs down to exact manufacturer part numbers based partially on 'meaningless' markings! – user36129 Jul 30 '15 at 19:55
• Perhaps i should rephrase. The markings on a semiconductor are meaningless to us unless we are the manufacturer or the markings a listed in the data sheet. – vini_i Jul 30 '15 at 20:08