# Electricity? 25x 3.3 volt diodes connected to a 12volt rail.. how?



## Fapguy (Oct 2, 2008)

The title says it all, i got 25x 3.3volt diodes, and i need to connect them to my PC's 12v psu, hows that?  what resistance do i need and how would i put it together?


thanks alot, pictures describing how would be ALOT of help, haha, im planning on putting them in a long row in the side of my pc.


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## Fapguy (Oct 2, 2008)

Size: 10m
Intensity max: 16000mcd
Spread angle: 17~23°
Voltage: 3,0-3,6V
Power: 25mA
Wavelength? (peak): 528nm
Material: GaInN
Temperature: -20°C - 85°C
Solder: 260°C in 5 seconds max.


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## Done_Fishin (Oct 10, 2006)

you say that they are 3,3V and use 25mA. You will feed from 12V.

best thing to do is place them in series 

they have polarity so you will need to ensure that they are polarised correctly to each other and the voltage rail.

since they are 3.3V each you can only use 3 at a time & you would need to make 8 banks if you want to use most of them I would protect them against reverse polarity (accidentally connecting the voltage in reverse) with a protection diode 1N4001 is a very easy Diode to find and is good for 1Amp and protects up to 50V reverse Voltage.
LED's do not like being connected in reverse polarity, whilst you might be lucky at low voltages (equal to it's own voltage) higher voltages than the forward drop are likely to fry them. Hence the protection diode.

*3 * 3.3 = 9.9 *( 3 diodes, voltage drop approx 10V)
*12-9.9=2.1* (difference in voltage between source and load)
*2.1 - 0,7=1.4 *(voltage after drop through 1N4001)

we now need to drop that 1.4V through a resistor at 25mA.

1.4V divided by (25/1000) = (1.4 * 1000)/25

rule of thumb
if instead of 1.4 we had 1.6 the the answer would be 400
if instead of 1.4 we had 1.2 the the answer would be 300

so with 1.4 we would have 350 .. (split the difference between 400 & 300)

resistors that could be used are 330Ω, 360Ω or 390Ω

resistor rating in power P=I*V OR P=(V*V)/R
25mA * 1.4V = (25 * 1.4)/1000 or approx 350mW

so your resistor would need to be approx 0.5W or 500 mW.

so for each bank of LED's

one diode 1n4001
one resistor 390Ω 0.5W
3 LED's.
Yellow and Black cable 
method of connecting to 12V supply


> Positive rail ----- (yellow +12V) 1Ν4001 (Anode) ----|>---- (cathode) ----390Ω----- LED1-(Anode) ----|>---- (cathode) - -LED2-(Anode) ----|>---- (cathode) - -LED3-(Anode) ----|>---- (cathode) - negative rail (black wire)


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