Japanese part numbering

[mobyd]

With comp pairs,why is the NPN number always bigger than the PNP ?.
i.e. 2SA1943 - 2SC5200
2SA1302 - 2SC3281
2SA1673 - 2SC4388 etc etc
M

[godfrey]

As opposed to:
BC547 - BC557
BD139 - BD140
Hmm...

For that matter, how come the "complimentary" part numbers are completely unrelated? Doesn't make it any easier to remember.

[sregor]

I'm sure there is a more complete explanation, but my experience is: They don't assign numbers by complements, but by the order in which companies apply for registration, which means that the reason the 2SC numbers are higher are that there are more types of NPN transistors than PNP transistors. If you go back far enough, the 2SA numbers were originally larger than 2SC numbers (germanium PNP is more common than NPN). Orignally 2SA and 2SC were high frequency, and 2SB and 2SD were power types, but the lines are very blurred these days.

[Steve Dunlap]

You didn't mention the 2SD555 and 2SB600.

[event horizon]

How about MJ802 & MJ4502 In this case the 802 is NPN..

I think it might have something to do with the wider use on N channel devices in the Japanese case (as mentioned by sregor), that's a guess though

[satoru]

sregor is right. Once upon a time, the numbering of Japanese transistors was handled by an independent organization, which assigned numbers (registration number) as they came in. There were more NPN registration than PNP so generally NPN number was higher for complementary pairs. Individual companies didn't have control over the number so PNP and NPN numbers got totally unrelated (any exceptions?? Someone, please pitch int your knowledge to correct me!).

The organization is no longer there and each vendors are now free to number theirs. New Toshiba parts will be TTAxxxx (PNP high freq), TTCxxxx (NPN high freq), TTBxxxx (PNP low freq), TTDxxxx (PNP low freq), etc. The well known pair 2SA1943/2SC5200 is now replaced by TTA1943/TTC5200 (with some improvement on spec), for example.

Satoru