SMT Equivalent of 2N3904 Transistor?

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damien_d
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Posted by damien_d: Sat. Dec 29, 2012 - 03:09 AM
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Dear all,

I'm looking for a SMT NPN transistor about the equivalent of the 2N3904, say in a SOT-23 package or similar? Normally I'm a software guy, but I am trying to create a really cheap design for my Dad's model train club :)

The original in a TO-92 package looks to go for under 10c in 1K volumes, which would be rather nice :)

Ideas?

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Learning and Information, General Electronics
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damien_d
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Posted by damien_d: Sat. Dec 29, 2012 - 03:12 AM
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Oops... I feel like a dill... the MMBT3904 is the ticket, but I'm still open to suggestions :)

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jgmdesign
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Posted by jgmdesign: Sat. Dec 29, 2012 - 05:15 AM
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2N2222A, 2N4124?

Google "General purpose NPN transistor" and see what happens.

I entered "NPN transistor" in one of digikeys searches and got 16,000+ possibilities :shock:

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damien_d
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Posted by damien_d: Sat. Dec 29, 2012 - 05:35 AM
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jgmdesign wrote:
I entered "NPN transistor" in one of digikeys searches and got 16,000+ possibilities :shock:

... which is precisely the problem :)

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mckeemj
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Posted by mckeemj: Sat. Dec 29, 2012 - 06:56 AM
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I actually like Digikey's search ( as distributor parametric searches go ). Drill down through it by adding requirements and sort by most important factor. The MMBT2222ALT3G from ON Semiconductors looks nice. It's got a 600mA rating, minimum gain of 100, comes in SOT-23 and is $0.10/25. Time to find... thirty seconds ( Discrete Semiconductors->Transistors (BJT) - Single, search for In-Stock, NPN, hfe > 100, surface mount - sort price ascending ).

Martin Jay McKee

As with most things in engineering, the answer is an unabashed, "It depends."

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damien_d
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Posted by damien_d: Sat. Dec 29, 2012 - 07:31 AM
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Any other particularly common ones that "everyone" uses?

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Plons
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Posted by Plons: Sat. Dec 29, 2012 - 12:42 PM
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BC547/548/549. In smd these are called BC847 etc. Their max Ic=100mA though.

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damien_d
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Posted by damien_d: Sat. Dec 29, 2012 - 10:46 PM
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Plons wrote:
BC547/548/549. In smd these are called BC847 etc. Their max Ic=100mA though.

I was wondering what they were called in SMT :)

-- Damien

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Plons
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Posted by Plons: Sat. Dec 29, 2012 - 11:03 PM
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Lovely huh ? Just add 300 to the partnumber.

BC847 in package SOT23 for the single ones, but there are also duals: BC847BPN in SC-88 (or SOT363)

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alexan_e
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Posted by alexan_e: Sat. Dec 29, 2012 - 11:25 PM
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I like these two (NPN/PNP), rated to 30v/700mA with high gain

http://www.unisonic.com.tw/datas...
http://www.unisonic.com.tw/datas...

Alex

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damien_d
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Posted by damien_d: Sat. Dec 29, 2012 - 11:45 PM
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alexan_e wrote:
I like these two (NPN/PNP), rated to 30v/700mA with high gain

Fortunately, the design (bi-colour LED driver, with latch) is rather tolerant of low (and variable) gain :)

-- Damien

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alexan_e
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Posted by alexan_e: Sun. Dec 30, 2012 - 12:20 AM
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Basically you can use a higher base resistor and limit the current that the AVR pin has to provide.
This can be useful in some cases or maybe to reduce the consumption.

I find these transistor especially useful for some ARM mcu that can provide only 3mA per pin.

Alex

"For every effect there is a root cause. Find and address the root cause rather than try to fix the effect, as there is no end to the latter."
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