Odd ST labeled transistor, what it may be? - Page 1
Forum section: electronics / projects

author: ceoxrad
author_rank: Regular Contributor
timestamp: October 01, 2020, 08:57:14 pm
content: Hello,I came across a little bunch of these strange transistors from surplus.They are simply marked POLY 3 and the manifacture seems to be ST.Using a transistor tester I determined they are NPN with a measly hfe of 3-4, also with a multimeter I can see junctions compatible with an NPN transistor (Vf be = 0.735V Vf bc =0.586V).I wasn't able to find a datasheet and even though they are simple parts I would like to know more and use them.Somebody has a clue? Custom part or part number for off the shelf silicon maybe?Thank you in advance!

author: bob91343
author_rank: Super Contributor
timestamp: October 01, 2020, 11:22:03 pm
content: Contact STMicroelectronics.

author: greenpossum
author_rank: Frequent Contributor
timestamp: October 01, 2020, 11:29:09 pm
content: Any chance you got C and E swapped which would lead to low hfe? Also which terminal is connected to the tab?

author: ceoxrad
author_rank: Regular Contributor
timestamp: October 02, 2020, 09:14:31 am
content: I used an automatic transistor tester, so the terminals were identified by it.The pinout reported makes sense because it's the usual one for power BJT in that package.Also the multmeter test agrees.The collector is connected to the tab and the pinout is from left to right B-C-E.

author: greenpossum
author_rank: Frequent Contributor
timestamp: October 02, 2020, 11:03:34 am
content: Maybe the low gain is why they ended up in surplus?

author: ceoxrad
author_rank: Regular Contributor
timestamp: October 02, 2020, 11:50:00 am
content: Yeah, that is possible, but it does not explain the wierd part number I guess.

author: razvan784
author_rank: Regular Contributor
timestamp: October 02, 2020, 12:25:23 pm
content: Some kind of engineering sample?Send it to Noopy to decap it and photograph the die.

author: Zero999
author_rank: Super Contributor
timestamp: October 02, 2020, 12:54:06 pm
content: Quote from: greenpossum on October 01, 2020, 11:29:09 pmNo, C & E must be correct, as VBE> VCB, because the base-collector junction is the larger.

author: brabus
author_rank: Frequent Contributor
timestamp: October 02, 2020, 01:31:46 pm
content: Have you bought them from a notorious surplus distributor based in Catania?

author: Labrat101
author_rank: Unknown
timestamp: October 02, 2020, 01:38:13 pm
content: The POLY 3 was use on some organic film transistors .that were manufactured have no idea if they have any advantage over regular transistors .

author: ceoxrad
author_rank: Regular Contributor
timestamp: October 02, 2020, 01:41:04 pm
content: Honestly this was many years ago (I dug out a lot of misc components I bought at the time to sort them out a bit).I think I know the dealer you mention, I bought something from him not sure if these came from them.They were in a bag with other old transistor, all standard parts.

author: ceoxrad
author_rank: Regular Contributor
timestamp: October 02, 2020, 01:43:50 pm
content: Quote from: Labrat101 on October 02, 2020, 01:38:13 pmI found some papers on the topic in my (vain) research of a datasheet, can those be it?I did not expect that kind of transistor in a power package like this one, and that should be a FET of some sort, do you think is that?

author: Labrat101
author_rank: Unknown
timestamp: October 02, 2020, 01:47:46 pm
content: The only thing I know is they were produced around 2005 .Do you have a transistor tracer . it would be interesting to see the trace on such a low Hfe .it should have a fairly fast switching speed .

author: ceoxrad
author_rank: Regular Contributor
timestamp: October 02, 2020, 02:05:03 pm
content: Sadly I don't, but probably I can find one, maybe at University in Physics dept. (where I'm currently studying) they have something.Or maybe I can trace the curves manually.

author: Zero999
author_rank: Super Contributor
timestamp: October 02, 2020, 02:29:57 pm
content: Quote from: ceoxrad on October 02, 2020, 01:43:50 pmIt appears to be the SOT-93, a common package for BJTs and probably pre-dates the power MOSFET. The TIP33 is another BJT commonly found in that package.https://www.mouser.com/datasheet/2/54/tip33-307823.pdfQuote from: ceoxrad on October 02, 2020, 02:05:03 pmYes, it's possible to trace the curves manually. It's fairly easy. I'd do it by connecting a resistor between the base and collector and another resistor from the collector, to a positive supply, with the emitter to 0V. You can easilly work out the base and colllector currents, using Ohm's law.

author: Labrat101
author_rank: Unknown
timestamp: October 02, 2020, 06:22:16 pm
content: I have a funny feeling that the Poly3 have a limited shelf life . The organic material degrades .Don't quote me on this one . bit like the OLED it just dies .If you have a few I would take them to your University and see if they all have the same properties under test .I am sure they have a good transistor tester with all the frills & tracesThere is a chance its a form of Darlington which registers as a single NPN on the new uni testers .Which might also account for the case size.