2n222 vs 2n3904

Thread Starter

DT tech

Joined Nov 4, 2022
1
I'm trying to make the following circuit which specs a 2n222, I've got stock of 2n3904's which I was hoping to substitute. Am I barking up the wrong tree?
 

WBahn

Joined Mar 31, 2012
27,933
Whether it's wrong depends on what transistor the video is actually using. If they are using a P2N2222A, then the it is correct. But if they are using a 2N2222A or a PN2222A, then it is wrong.

1667571396113.png

Gotta love it.

https://media.digikey.com/pdf/Data Sheets/ON Semiconductor PDFs/P2N2222A Rev3.pdf

As for whether using the 2n3904 should work, I think it will likely work better. The 3904 has it's current gain peak right around 10 mA, which is about where you will be operating with a 470 Ω current-limiting resistor. The 2n2222 peaks closer to 100 mA. It's probably not going to be enough to be really noticeable, however. But since the base current has to flow through (or along) your skin resistance, you want all the current gain you can get.
 

dl324

Joined Mar 30, 2015
15,475
I'm trying to make the following circuit which specs a 2n222, I've got stock of 2n3904's which I was hoping to substitute. Am I barking up the wrong tree?
Are you certain they didn't specify PN2222? 2N2222 is in a metal can.

That circuit would work if it was using something like BC547.

2N+BCpinout.jpg
Note that BCX has a reversed pinout that makes it match 2N devices.

The other pin order for TO-92 (for 2SC devices) is:
1667572667017.png
 

wraujr

Joined Jun 28, 2022
40
I think he needs a resistor in the base path as protection if someone were to use metal to short contacts.
With Ic at 10mA and Beta=100, the base current typically needs to 0.1mA.
Assume a 10:1, limit base current to 1mA with (9V-0.7V)/1ma = 8.2K approx.
 
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