So my part is a 2n2222a331. I don't know who the exact manufacturer is since I can't find the datasheet. Both these datasheets I found say they are from On semi, but one says Fairchild now a part of On semi. The other one is just On semi data sheet.

Not sure which one to trust. I've read they can work both ways which I'm seeing happen. Swapping C and E I can pull current through both ways to turn on a high-side LED. Is there a voltage drop across the pins I can know which one is the correct direction? I assume one configuration will have a higher/lower voltage drop between C and E pins to dictate which is the correct way.

https://www.jameco.com/Jameco/Products/ProdDS/178511v1.pdf
https://www.onsemi.com/pdf/datasheet/p2n2222a-d.pdf

 

Ah nevermind I see the P2N2222a is the difference, which is why the pin layout is different.

 

So my part is a 2n2222a331. I don't know who the exact manufacturer is since I can't find the datasheet. Both these datasheets I found say they are from On semi, but one says Fairchild now a part of On semi. The other one is just On semi data sheet.

Not sure which one to trust. I've read they can work both ways which I'm seeing happen. Swapping C and E I can pull current through both ways to turn on a high-side LED. Is there a voltage drop across the pins I can know which one is the correct direction? I assume one configuration will have a higher/lower voltage drop between C and E pins to dictate which is the correct way.

https://www.jameco.com/Jameco/Products/ProdDS/178511v1.pdf
https://www.onsemi.com/pdf/datasheet/p2n2222a-d.pdf

Datasheets do not contain exact numbers. What they contain is a collection of random variables, each with it's own mean and standard deviation. It is a reasonably accurate description of the parts that come off the assembly line.

 

 

Ah nevermind I see the P2N2222a is the difference, which is why the pin layout is different.

Back in the day (70's), 2N2222A were in metal cans.

 

It's crazy because for the longest time I've been using this transistor in the "P"2n2222A configuration. At least I think that is what happened when building my circuit. Probably read the wrong datasheet. So I've had it backwards, though it works fine at voltages around 5V or less to have it backwards. Today I tried to use it at 12V and all of a sudden things went wrong. So I can't believe this whole time I had my circuits with backward NPN transistors. Fun.

 

View attachment 260891

Who's awful idea was that? How many poor folk used the wrong image??

 

This is one reason I keep one of these around. This particular one turned out to nbe pretty good, but I think you can find one that looks the same for a few dollars less.

​

 

So I've had it backwards, though it works fine at voltages around 5V or less to have it backwards. Today I tried to use it at 12V and all of a sudden things went wrong. So I can't believe this whole time I had my circuits with backward NPN transistors.

With the collector and emitter reversed, you were operating the transistor in inverted mode. Whether it will works depends on the beta the circuit needs to function. When you increased the emitter-base reverse bias to more than about 5V, the junction broke down. Beta may have been damaged if there was sufficient reverse current.

 

"2n2222a331" If you bought that recently, with that date code (331) it is probably an un-branded part that is something like the transistor you wanted.

As noted previously there is a lot of variation among '2222's and buying an unbranded part can lead to problems. The one in the picture is advertised to be rated at 800 ma -really? First time I have ever seen that kind of collector current associated with and '2222, and probably an inflated figure.

It is easy enough to buy from a reputable dealer and know for sure who the manufacturer is, and in my own opinion it is worth paying a little more to know what I am buying and have the correct datasheet on file.

 

I remember lots of confusion around BC182K and BC182L which have different pin configurations.

 

Back in the day (70's), 2N2222A were in metal cans.

You can still get the 2n2222A in the TO-18 case.

 

You can still get the 2n2222A in the TO-18 case.

2N2222A should always be in a metal can. The problem is that it appears that you can get 2N2222A in plastic. Those devices won't have the same power dissipation capabilities and should not be using the 2N part number. PN2222A is a more appropriate part number for the transistor in plastic.