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problem with 5mm leds Answered

i make a 5mm(3.3v) white  6 led series and run it by 5v adapter without any resistor but after running feu hours 1 or 2 leds slowly lost it's brightness and then it's off
i can't understand what is the problem
please help.....

Tags:leds

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iceng

Best Answer 10 months ago

five leds in series will need a resistor in series and 18v DC..

When 5v is put on a single 3.3v led you are destroying your leds with 1.7 too much voltage that pushes too much current through led and hurts the semiconductor..

You need to put a 68 ohm resistor in series with each led across 5v !

Click the pic to see the whole image..

18 VOLTsolution.png
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neelpaliceng

Answer 10 months ago

there is defiant (watt like 1/4,1,2,5) what i use????

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neelpalneelpal

Answer 10 months ago

is 68 ohm and 68kilo ohm is (=)

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icengneelpal

Answer 10 months ago

68 ohm if you want 25 milliamp to light your LED

68Kilo ohm if == 68,000 ohm. Kilo means x 1000

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icengneelpal

Answer 10 months ago

Resistor power = resistor volt x amperes = 1.7 x .025 = .0425 watt.

You can use an 1/8 watt resistor or a 1/4 watt if that is all you have on hand.

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rickharris

10 months ago

Limit the current with a resistor.

look up the data sheet for your LED if you can it will tell you the reccomended current.

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steveastrouk

10 months ago

You have to put a resistor in series with them.

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Downunder35m

10 months ago

With those specs there is no chance the LED's would turn on on 5V if connected in series.
I guess you connected them in parallel.
This would explain them going dim and dead as they burnt out from the overload.
It is always advised to use the right resistors to limit the current the LED(s) can get.