# 2n 3904 NPN Info Please???

Discussion in 'The Projects Forum' started by dyeraaron, Jan 20, 2010.

1. ### dyeraaron Thread Starter Active Member

Oct 27, 2008
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Good morning....I was wondering if somebody could help me out with a little info..I'd appreciate it.....so I working on a circuit at home that deals with a lighting sequence and I'm using 3904 NPN transistors to make the LEDs brighter....I've noticed that all 3904's are not the same....The only one I had that actually worked how I wanted it to ( which I only had one of) the writing on it said 2N 3904 730 below it.......what does this 730 mean? I've seen others that say like 2n 3904 with a 415 or something like that under the 3904 as well.

Jan 18, 2008
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3. ### Jack_K Active Member

May 13, 2009
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There are two different lead configurations for the 2N3904. Maybe you have some of each?

Jack

4. ### SgtWookie Expert

Jul 17, 2007
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Actually, all 2N3904 transistors in a TO-92 plastic case should have the same lead configuration.
With the flat face towards you, pins down, from left to right:
1: Emitter
2: Base
3: Collector

I would connect them like this:

Just two shown to keep the schematic simple.

R1-R3 calculated for Vcc/Vdd=5v, Vf(LED) = 2v @ 20mA
Since I'm using the transistors as saturated switches, Ib=Ic/10; since desired Ic=20mA, Ib=2mA
Rbase = (Vcc-Vbe)/2mA = (5v-0.7v)/0.002 = 4.3/0.002 = 2150 Ohms. You could use 2.1k or 2.2k.
Rled >= (Vcc-Vf(LED))/20mA = (5v-2v)/0.02 = 3/0.02 = 150 Ohms.

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5. ### beenthere Retired Moderator

Apr 20, 2004
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They should be EBC for new ones, but older manufactured ones are probably BCE. There was some real confusion until the TO-92 pinout got standardized. Just wait until you realize you have both pinouts in the same drawer.

Dec 20, 2007
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