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200 LEDs

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watzmann

New Member
HI All ,

i'm going to connect about 200 red LEDs in parallel ,

so i'll write you here what i'm going to do and tell me please if i have something wrong .

i'll run this led matrix of 200 led with adapter 4 volt , and i'll put just one resistor of 470 ohm but with high power

power = I x V
= 0.25 mA * 4 = 1A

so i'll use resitor of 470 ohm and 1 watt.

please tell me if i wrote something wrong ,
 

ericgibbs

Well-Known Member
Most Helpful Member
watzmann said:
HI All ,

i'm going to connect about 200 red LEDs in parallel ,

so i'll write you here what i'm going to do and tell me please if i have something wrong .

i'll run this led matrix of 200 led with adapter 4 volt , and i'll put just one resistor of 470 ohm but with high power

power = I x V
= 0.25 mA * 4 = 1A

so i'll use resitor of 470 ohm and 1 watt.

please tell me if i wrote something wrong ,
hi,
Never connect LED's in parallel.!

Problem is, they are not perfectly matched in their forward voltages.

The LED with the least voltage drop will take all the current until burns out, then the next one will burn.... it will be a run away....

EDIT:
Also your sums are wrong.

200 diodes * 0.025A = 5Amps..

Assuming a LED Vfwd of say 2V, you have to drop 2V at 5A = 0.4R ... = 10Watts..
 
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ericgibbs

Well-Known Member
Most Helpful Member
watzmann said:
so what is better to do ?....... series ,

but in that case i'll put a resistor for each one , right ?
What is the forward voltage drop of the LED's and what power supplies do you have.?
 

ericgibbs

Well-Known Member
Most Helpful Member
watzmann said:
i'm using 5mm red Leds, so it has 3.3 volts and the power supply is adapter of 4 volts
That means a resistor for every LED.!

Resistor = (4V - 3.3V)/.025A= 280R ,, 0.125W

For explanation, if you had a 12Vdc power supply, you could connect 3 LED's in series with just one resistor.

R= (12-9.9)/0.025 = 84R,,, 0.125W

Is that clear.?

EDIT: Dont forget if use a resistor for each LED, if the are all ON, you need a 5Amp, 4V psu.!!!
 
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ericgibbs

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Most Helpful Member
watzmann said:
how long do you think ,will it stand if i connected it in parralel mode
About the same time it took you to type this post..:eek:
 

audioguru

Well-Known Member
Most Helpful Member
I bought a factory-sealed bag of 100 red LEDs from Fairchild. Their forward voltage is almost exactly the same and they could be connected in parallel with a very small difference in current and brightness between them.

But I would not connect them directly in parallel because if I ever needed to replace one then it wouldn't match the forward voltage of the others.

Many LED arrays have the matched LEDs connected directly in parallel.
 

watzmann

New Member
audioguru said:
Many LED arrays have the matched LEDs connected directly in parallel.

and i did that before many times , that was for about 150 LED connected together in parralel and they are working since 3 months !!!

i'll go on connecting them in parrallel.

more easier ..... less components., less voltage .
 

Torben

Well-Known Member
watzmann said:
more easier ..... less components., less voltage .
. . .less reliable, poor design. . .

You're safer to raise the supply voltage and put them in parallel strings of LEDs, with each LED having its own resistor. You can use a calculator like this one if you need help with the math.


Torben
 

blueroomelectronics

Well-Known Member
watzmann said:
and i did that before many times , that was for about 150 LED connected together in parralel and they are working since 3 months !!!

i'll go on connecting them in parrallel.

more easier ..... less components., less voltage .
Since you're just going to ignore good advice why did you bother asking?
 
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