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I have the following in my circuit:

enter image description here

Am I right in understanding that the pins top to bottom are:

1/Emitter 2/Base 3/Collector

where the top square pin is Emitter, middle pin with red trace is the Base and the bottom pin would be the collector?

The datasheet is here: https://www.sparkfun.com/datasheets/Components/2N3904.pdf

Many thanks!

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  • \$\begingroup\$ Um, where's the link to the datasheet and what does it say? You have no pin numbers on the PCB so presumably 1 is the square pad but which order are the other two? \$\endgroup\$ – Transistor Jan 4 at 14:25
  • \$\begingroup\$ Added the datasheet \$\endgroup\$ – RenegadeAndy Jan 4 at 14:33
  • \$\begingroup\$ @RenegadeAndy you added the datasheet literally a few seconds before I posted my answer! I have linked a different datasheet, but it is the same component. \$\endgroup\$ – MCG Jan 4 at 14:35
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Yes, you are correct in your pinout. If you look at the DATASHEET, then you can see which pins are what.

enter image description here

Luckily, you have your silkscreen showing where the 'flat' side of the transistor should be facing. Using that, and the picture from the datasheet, you can see that the top of your screenshot), you have pin 1, then 2, then 3.

Checking this on the Datasheet, it is indeed Emitter, Base, Collector.

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  • 4
    \$\begingroup\$ Some folks erroneously assume that all flat-sided transistors have similar pinouts. A few are CBE, others (Asian?) are BCE. Haven't seen any such deviations on 3904 from various makers. (2222 types DO have variations). \$\endgroup\$ – glen_geek Jan 4 at 14:47
  • \$\begingroup\$ 2222 types may have variations (I didn't know that!) because the "real" 2N2222 calls out a metal package, not a TO-92, so any plastic "2222" is, at best, a 2222 die in a non-standard package. I have certainly seen variations on the usual pinouts -- at least in the case of a few RF types I've run across it's clearly been for layout considerations (putting the emitter in the middle gives better isolation for a common-emitter circuit, for example). \$\endgroup\$ – TimWescott Jan 4 at 17:13

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