Beware the P2N2222A!

I was working on a simple 16MHz Pierce oscillator recently, built around a 2N2222 transistor. Nothing special, should work without any trouble, right?

Nope. The darn thing just wouldn’t oscillate! I found that it would oscillate below about 10MHz, but not above that. After some testing of the transistor, I found that it only had a beta of about 3, and its base-collector breakdown voltage was 8 or 9 volts!

Not only that, but I had 5 such transistors, all exhibiting the same behavior, and all with the same part markings:

P2N2222A E02

P2N2222A E02

Now I’ve bought a lot of 2N2222 transistors, so I wasn’t sure who the actual manufacturer was, but I was sure that somehow I’d gotten a bad batch of transistors. I was just about to Widlarize them all, when I decided to put it to the EEVBlog forums.

Several of the commenters asked if I was sure that I didn’t have the transistor in backwards. Well I’m quite familiar with the standard 2N2222 pin out, so I hadn’t even considered that to be an issue, and I was sure that wasn’t the problem. That is, until Kevin.D pointed out that what I was seeing was in fact indicative of swapping the collector and emitter pins: low beta, and low base-collector (which, if swapped, is actually the base-emitter) breakdown voltage.

Doh!! That was exactly the problem, and had I bothered to look it up, Wikipedia would have told me that too:

2N2222 pinout variants; note the “PN2” vs “P2N” part prefixes

You’d think by this point in my life I would have learned to stop making assumptions… 😛

The Art of Electronics Rant

The Art of Electronics (AoE) is perhaps the most popular electronics book of all time, often referred to as “the bible”. But while many people, myself included, have found it illuminating, many others deride it for its apparent disorganization and lack of theory. For this reason, there are often heated debates regarding its usefulness as a beginner’s electronics book.

Certainly AoE isn’t “the book” for everyone interested in electronics; I don’t know of a single text that is. But AoE is the book that finally helped me start understanding electronic circuits, something that many other electronics books before it failed to do. So I think it would be beneficial to address the two most common criticisms of AoE that I’ve seen, and discuss why AoE was a great help to me.

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