Why use 2N3904 vs 2N2222?

[FriedMule]

Just a short and hopefully simple question.
2N3904 = max 200mA
2N2222 = max 1A
Rest looks about the same

I am thinking why is the 2N3904 so populare, why not just use 2N2222 all the time or even maybe a max=5A all the time?
I do also wonder the same about other components, why 1/4 w instead of 1w or why 10V caps instead of 60V?

I know that the price can differ but its about a few cents and to home use, it do not kill the budget. :-)

[exe]

Afaik they have different gains at different currents. Compare at what current they have maximum gain (10mA for 2n3904 vs 150mA, I used on semi datasheet).

[windsmurf]

Price.

[ledtester]

I do also wonder the same about other components, why 1/4 w instead of 1w or why 10V caps instead of 60V?

Size can matter -- 1W resistors are bigger (and more expensive) than 1/4 W. 60V caps are larger for the same capacitance than 10V caps.

[bd139]

There's not much in it apart from price and collector current. I tend to use 2n3904 for most things though. It's cheaper.

[exe]

I use 2n3904 because it was my first bjt and I have plenty of them. So, emotional attachment.

[mariush]

I do also wonder the same about other components, why 1/4 w instead of 1w or why 10V caps instead of 60V?

1/4w resistors will probably be cheaper, and use less surface on a circuit board.  Also, there's surface mount 0805 resistors which are rated for 0.1w and can be more convenient to use (for example value printed on them, big enough to solder by hand on pads, just the right size to fit between two through holes 0.1" apart, so great to use on prototyping boards)



^ The above are 1206, pins are 0.1" apart... 0805 are not much smaller so you can see how they'd fit right between two holes.

As for capacitors, sometimes you need specific characteristics. For example you may want to use a cheap *1117 linear regulator to get 3.3v out of 5v, and these particular linear regulators need an output capacitor on the output with ESR between 0.1 ohm and 1 ohm. In this case, a 47uF 10v-16v electrolytic capacitor would have just the right ESR while a 47uF 50v electrolytic may have less than 0.1 ohm ESR (depends on series)

Sometimes you want higher voltage, for example if you absolutely have to use tantalum capacitors, it's often recommended to use 1.5-2x the voltage rating, as they tend to burn or explode on overvoltage.

With ceramic capacitors there's the issue of voltage bias, and you may have use higher voltage rating capacitors just to guarantee some minimum capacitance ... see : https://pdfserv.maximintegrated.com/en/an/TUT5527.pdf

Sometimes you would pick a higher voltage rating than you need just because the capacitor would be a bigger volume and the cost savings are minimal or non-existent, and there's benefits to having a bigger volume capacitor.

For example, a lot of computer switching power supplies will use 10v or 16v rated electrolytic capacitor on the 5v stand-by circuit, even though a 6.3v rated electrolytic capacitor could be used - as this 5v stand-by portion is running 24/7, even when the computer is shut down, even when the power supply has the fan turned off, it makes sense to have a bigger capacitor that can handle better the heat produced by this 5v stand-by circuit, and have a higher lifetime rating.

[FriedMule]

Okay thank a lot for all your answers, that make it a lot easier to understand.
Take what you have unless some specific situation including money, so it is good to have some to choose between:-)

[Zero999]

The 2N2222 won't last long at 1A. It's rated for a maximum of 800mA continuously. No doubt you can run it at higher currents, if the case is soldered to a piece of copper to act as a heat spreader and fixed to a heatsink, but it's easier to use a more higher powered transistor.

[Howardlong]

I use 2n3904 because it was my first bjt and I have plenty of them. So, emotional attachment.

My first was an OC71. Frankly, I’m not quite so emotional about them. Sentimental maybe. 

[netdudeuk]

I use 2n3904 because it was my first bjt and I have plenty of them. So, emotional attachment.

My first was an OC71. Frankly, I’m not quite so emotional about them. Sentimental maybe. 

Ladybird book radio project ?  I had to use salvaged AC125 / AC128 IIRC.

[mikerj]

I use 2n3904 because it was my first bjt and I have plenty of them. So, emotional attachment.

My first was an OC71. Frankly, I’m not quite so emotional about them. Sentimental maybe. 

Ladybird book radio project ?  I had to use salvaged AC125 / AC128 IIRC.

That book was my first introduction to transistors.  We had an little shop in town that sold electronic components from a huge wall of those little plastic drawers, and a proprietor that was knowledgable and helpful.  Some things definitely were better in the past.

[Alex Nikitin]

Compared to the 2N3904 the 2N2222 is a larger (higher capacitance and maximum currents, lower saturation voltage at high currents), slower, considerably lower noise device.

Cheers

Alex

[exe]

Interestingly enough, both parts have same noise figure in onsemi datasheets. Although, I'd expect bigger part to have less noise.

[schmitt trigger]

The 2N2222 is the metal can version (TO39).
The plastic version, is called PN2222 (TO92), and is nowdays the most ubiquitous one, for cost reasons.

[bd139]

Interestingly enough, both parts have same noise figure in onsemi datasheets. Although, I'd expect bigger part to have less noise.

Depends on the manufacturer.

The 2N2222 is the metal can version (TO39).
The plastic version, is called PN2222 (TO92), and is nowdays the most ubiquitous one, for cost reasons.

There are two versions of the PN2222 as well with different pinouts 

[boffin]

2N4401 offers a pretty nice in-between the two (at a similar price to the 3904), it's the generic NPN that my project drawer is filled with.

[T3sl4co1l]

4401 is generally better specified than 2222.  I never use 2222.

2222 is in the same class for me as 3055 and such.  Old, old part, specs looser than a street corner hooker.  You never know what you're going to get.  Floor sweepings?  RF power transistors?

I default to 3904 for a general purpose, low current transistor.  It's faster than 4401 at the same currents.

Higher currents are handily served by low-Vce(sat) types like PBSS303NX/PX, which have a number of other nice features.

Higher speeds are disappearing quickly, but for the time being, MMBTH10 and MMBTH81 are still around.  BFT92 is gonski.

Tim

[schmitt trigger]

I do also wonder the same about other components, why 1/4 w instead of 1w or why 10V caps instead of 60V?

Another excellent reason is size. Have you compared the size of a 10V, 1000 uF cap vs. a 63V, 1000 uf one?

[jackthomson41]

I think it's just the price. If you are designing a product and you want like 50k pieces then you can save money by using 2N3904 instead of 2N2222, provided it matches your current requirement.

You can also use BC547, which is even cheaper then above two.

[Giuss]

I use in most cases BC547 or 557 (pnp)

For higher currents BC337 is a good and cheap choice

[kosine]

I've always referred to them as a "quad-2", because it's quicker to say.

Officially though, they're a "twenty two" - "twenty two" since they're part of the 2N22- range.

[Whales]

There are two versions of the PN2222 as well with different pinouts 

I had a bad day when I encountered this.  Old ones had C & E swapped compared to new ones.  They still "work" (BJTs are somewhat symmetric) but very poorly and often go pop. 

I now ignore the datasheets for all TO-92 BJT parts and use a transistor tester to tell me the pinout instead.   It also doesn't help when the odd datasheet doesn't tell you if it's a top or bottom view of the pinout

[Berni]

I think part of the 2N2222 popularity is the catchy part number like the NE555.

But 2N3904 or 2N2222 or BC847 or BC547... etc it usually doesn't matter. If you use this jellybean part then you probably don't have high requirements for it. You probably just needed a small signal transistor to do something with a signal, like invert a signal or turn on a LED or something. The sort of application that any general purpose NPN would work for, so you just take one of these very common jellybean NPNs because they are dirt cheep and you probably have a pile of them inside your parts drawers.

If you need to switch lots of power there are lots of better modern transistors that are also in a package better suited for dissipating the heat. If you need a fast switching high frequency transistor there are again lots of better modern parts. If you need something with a ton of gain, there are better modern parts. So if you are being picky about the performance specs of a 2N3904 then that is a sign that you should probably be looking for a more modern specialized transistor.

These transistors are like the "ducktape" of advesives. Everyone has it, works good enough for most use cases and so people will use it unless they have a reason to use something else more specialized.

[StuartA]

Back in 2008, a guy called Chris Task published a paper called "Evaluation of Bipolar Transistors Suitable for Active Antenna Amplifiers". A key characteristic which he was looking for was linearity, but other factors such as noise factor and frequency response came in. Of all the really cheap transistors, he seemed to think that the 2222 came out top and beat the 3904. Indeed, the 2222 has been used in some popular designs for magloop amps. See http://webcache.googleusercontent.com/search?q=cache:CRTLZ7XP8mQJ:www.ok1rr.com/dwnld/Bipolar%2520Transistor%2520Evaluation.pdf+&cd=1&hl=en&ct=clnk&gl=uk