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2N3904 and 2N4401 appear to be very comparable parts in all specs. 2N4401 has a higher current rating, but otherwise they look to be about the same in price and everything else. Obviously it's difficult to give a 100% universal answer since both parts are made by multiple manufacturers. But insofar as it is possible to say, is there any reason one would use a 2N3904 instead of a 2N4401?

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  • \$\begingroup\$ If the specs of the part fit better to the specs for the part you need, then you chose it. \$\endgroup\$ – PlasmaHH May 2 '16 at 14:08
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    \$\begingroup\$ When you order thousands of parts, sometimes these few cent differences are becoming non-negligible.. \$\endgroup\$ – Eugene Sh. May 2 '16 at 14:19
  • \$\begingroup\$ It can also depend on the circuit you're using them in, in a properly designed circuit either transistor would work fine (since they have very similar specs.) but if the circuit would rely on for example, a certain value of Vbe, then the choice of transistor could be critical. In practice such a circuit would be unpractical and unreliable since Vbe is very unpredictable even for the same type of transistor. So in my opinion: there is no reason to choose one over the other. \$\endgroup\$ – Bimpelrekkie May 2 '16 at 14:21
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    \$\begingroup\$ Various non-technical reasons- Eg. your company already has 150,000 2N3904 in stock and they are used in multiple products. Or the price is $0.001 cheaper and they work the same. Or a combination of the two- your company is buying the 2N3904 in mass quantity for cheap and you would have to buy the 2N4401 in 100 quantity for 5x the price and it would be a new additional inventory item to keep track of. \$\endgroup\$ – Spehro Pefhany May 2 '16 at 14:43
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    \$\begingroup\$ Hmm I used a 2n3904 in a cap multiplier, and had some oscillation/ excess noise issues... cured with a bit of R and FB in the base. A 2N4401 showed no such problems, so I used it... and kept the R and FB. (belt and suspenders.) \$\endgroup\$ – George Herold May 2 '16 at 15:47
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I use the 4401/4403 as my jellybean go-to transistors when it doesn't matter, and most of the time it doesn't. As you say, the 4401 and 3904 have similar specs, but there are differences. The 3904 is better at really low currents, but the 4401 can handle higher currents.

Most of the time the 4401 is good enough, so I "standardized" on it since it's more robust and I run into 100 mA applications more than 100 µA applications.

Once you pick something as your jellybean part, you want to use it whenever it's good enough. You don't want purchasing and manufacturing to have to deal with more different parts than necessary. Personally I think the 4401 is a better choice for this since it will be a fit to a few more applications than the 3904, at least for the things I tend to do.

I therefore don't use a 3904 at all. In the relatively unusual case where I need a lot of gain at very low currents, I'll use something else even more suitable. The 3904 is just too close to the 4401 that I use in volume to be worth stocking.

If you decide on the 3904 as your jellybean NPN, then you might still use a 4401 when you need more current than the 3904 can handle, up to a few 100 mA. That's because the 4401 is a really cheap part in that current range. Beyond that, you're going to use something else, probably a power transistor, anyway.

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  • \$\begingroup\$ @Tut: Oops. Fixed. \$\endgroup\$ – Olin Lathrop May 2 '16 at 17:15
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There may be good reasons for choosing the 2N3904 when working at lower current. The 2N4401's higher current capability comes at a cost - higher capacitance and much longer turn off time at low current.

Emitter-Base Capacitance:-

  • 2N3904 = 8pF
  • 2N4401 = 30pF

Storage time:-

  • 2N3904 = 200ns @ 10mA
  • 2N4401 = 225ns @ 150mA

enter image description here

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I have used both. But for different applications. For any audio pre-amplifier type of application, 2N3904 tends work better to bring the mic level signal to line level. The 2N4401 I use for higher current amplifier where you want to drive some relay or opto-isolator.

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