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I am repairing a "wall-wart" charger for a Black and Decker battery powered edger which uses a 12 volt/7 amp hour battery. It has ceased to deliver charge current to the battery but the half wave rectified current is present at what I think is the emitter of a TO92 cased device labelled "S8550". I have found confusing information trying to identify this device. I found a reference to an "SC8550" that is listed as a PNP silicon transistor but I have never seen an SC designation without the preceding "2". It does not check as a "good" PNP transistor using the DVM and I don't have access to a curve tracer.

Does anyone have experience with this "transistor"? If the info I found is correct then I guess I can search using the max ratings to find a sub. It is the only transistor on the small circuit board which also contains a quad op-amp.

I don't have a circuit diagram/schematic and I am unable to determine the purpose of this device except maybe it is a switch to supply charge to the battery until it reaches a specific charge level? Is it likely that a TO92 cased device would control current to charge a 7 amp hour battery or might this be a voltage reference?

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  • \$\begingroup\$ Note that you say "C8550" in the title but "S8550" in the text. I made the assumption that it was the latter in my answer. \$\endgroup\$
    – Edward
    Commented Aug 12, 2014 at 2:53

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This is a really common cheap and generic PNP power/switching transistor in mainland China. It's inspired by the 2SC8550, but specs and pinouts vary (usually Japanese or US pinout, IME).

Other similar part numbers are SS8550, SC8550 etc.

It is often quoted with a silly high power dissipation intended for audio output type ratings.

Example datasheet of a similar part here.

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  • \$\begingroup\$ As the original question/post says, there doesn't seem to exist a Japanese 2SC8550... \$\endgroup\$
    – got trolled too much this week
    Commented Dec 10, 2014 at 11:12
  • \$\begingroup\$ Also there's a book page listing common 2SCxxxx transistors on which the 8550 appears last but without the 2SC prefix, so I'm pretty sure there never was a Japanese 2SC8550. \$\endgroup\$
    – got trolled too much this week
    Commented Dec 10, 2014 at 14:33
  • \$\begingroup\$ Thanks, my Japanese reference does not go as far as that number. It would be interesting to get a definitive answer on the origins of this popular part. There are SMT versions with similar numbers (I have not looked to see if they're claiming 2W from an SOT-23!) \$\endgroup\$
    – Spehro Pefhany
    Commented Dec 10, 2014 at 14:47
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    \$\begingroup\$ I discovered that Samsung also makes this part as well as SS9011, so it might be them. I'm going to ask this as a separate question. \$\endgroup\$
    – got trolled too much this week
    Commented Dec 10, 2014 at 15:04
  • \$\begingroup\$ Samsung makes more sense to me than an Indian company. Also would explain the adoption in Asia and pseudo-Japanese numbering. Good luck with your question. \$\endgroup\$
    – Spehro Pefhany
    Commented Dec 10, 2014 at 15:17
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Looks like this PNP transistor which is spec'd at \$V_{CEO}=20\text V\$ and \$I_C = 700\text {mA}\$.

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  • \$\begingroup\$ Quite possibly, but beware there are devices from other manufacturers with higher current and/or higher voltage rating but the same label. I attempted to survey the alternatives in my answer. Alas we were not given a photo to work with here... \$\endgroup\$
    – got trolled too much this week
    Commented Dec 30, 2014 at 10:39
  • \$\begingroup\$ Since some future reader (with <10K rep) might be confused by the above comment and the absence of my answer on this page: I've deleted it after all I got for my troubles was a downvote with no comment. Apparently such answers aren't a positive contribution to this site, so you'd better do your (thorough) parts research elsewhere. \$\endgroup\$
    – got trolled too much this week
    Commented Jan 20, 2015 at 19:06

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