Transistors.. wich pin is wich?

[theMACHINE]

Hi..

Stupid question!

I'm new to all this, and I need to know how to figure out my transistors... I just wonder how you know wich pin is wich..?
Guess they are called B, C and E? If so, how so I know which one is wich?

[The Tone God]

Without knowing which transistor you are referring to we are guessing just as much as you.

Did you check out the DIY FAQ as well ?

Andrew

[caress]

http://www.diystompboxes.com/smfforum/index.php?topic=53991.0

using the search function helps, too.   

[Meanderthal]

 Usually you can google the part number, get the datasheet, and that'll tell ya.

[theMACHINE]

ahm.. yeah right... AC187

[dxm1]

Google is your friend...

http://www.datasheetarchive.com/search.php?q=AC187

[Mark Hammer]

I could be flippant and say "Just get the damn datasheet!", but the sad and frustrating truth of the matter is that sometimes the illustrations on them are a little ambiguous, and you're no farther ahead if you end up downloading the "wrong" datasheet for that particular tranny.  Of course if the number is missing or hard to read, how do you get the datasheet in the first place?

All transistors are essentially a pair of diodes, with either the cathodes or the anodes constituting the emitter and collector pins.  While you can use your multimeter's diode test to identify which of the 3 is the base and whether it is PNP or NPN (something they outline in an old Sam's and HEP transistor cross-reference), there is still the question to resolve of which is the emitter and which the collector.

Which brings us to the easiest solution:  Make sure you have a DMM with transistor hfe test.  Usually, these meters will have a 4-pin socket, labelled something like E-C-B-E.  This will let you easily test trannies with an E-B-C pinout or an E-C-B pinout, without having to twist the leads around.  When I have an unmarked or poorly marked transistor, I simply set the meter to NPN, and try different configurations until a get a reading of some reasonable or plausible hfe.  Then I switch to the PNP setting.  The component should show zero hfe in the "wrong" polarity-type.  If the readings don't make sense, I switch to the other pin configuration and the other polarity type.  Eventually you'll find an orientation and pinout where thereadings make perfect sense.  Note which pin is which, and away you go.

[theMACHINE]

Think i got it now... thanks.

[Papa_lazerous]

I just use one of these

http://www.maplin.co.uk/module.aspx?ModuleNo=31538&doy=27m2

[Papa_lazerous]

Ooops Silly John made it way HUGE, My Bad

that tool is great for matching FETS or Hfe on trannys quick

[MikeH]

That's awesome.  I was trying to decipher the pinout on an older tranny I had (The only data sheet I actually could find was from a different mfg. and the pinout was WRONG.  In fact, I couldn't even tell who the mfg. was) and I thought "They should make a device that you can plug a transistor into that tells you what the pinout is".  Apparently they do.

[Papa_lazerous]

They are great on some FETS they dont work though because it cant always determine the source and drain but knows which is the gate.  but then there is always R.G's JFET tester.....

It will test a Tranny tell you which leg is which and tell you the leakage and Hfe and the current used to test which is kinda important. it will tell you if it is PNP or NPN Si or Ge It will analyse Diodes too so its perfect for matching.

It knows if you hook it up to a darlington pair too. Its not cheap but has saved much time sorting through components plus its a dam cool gadget

[Mark Hammer]

That's a neat tool, but my sense is that it is not the sort of specialized equipment that someone who asks "which pin is which" is going to be springing for just yet.

Happily, it is pleasantly surprising just how many REALLY cheap DMMs (i.e., under $20) include transistor hfe testing as one of their features.

[Papa_lazerous]

Yeah you have a point there Mark its not the sort of thing you would just go and buy  just because you want to know the pinout of a tranny,

But its worth knowing what 'toys' are available me thinks. God knows boys like toys