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RSS >  problemwith led..., please help
journeyman68 #1 06/11/2010 - 21h22

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have problem with led...
power : 6v- 4 1.5v AA.
led- sfh485p
5mm.880nm
current forward if: 100ma
current if av:100ma
voltage vf typ:3v
resistor: 1/2 watt.5 % tolerance
but, not working. can some one help me please....
dewey1 #2 06/11/2010 - 22h21

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Need to know if series or parallel IR LED.
What resistor value in ohms for series?
What resistor value for each LED in parallel?

Do not run at 100mA, that is maximum continuous. 50 to 75 mA is typical.
journeyman68 #3 07/11/2010 - 03h35

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parallel.
journeyman68 #4 07/11/2010 - 03h37

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parallel,
its 33ohm,1/2 watt,5% tolerance..
dewey1 #5 07/11/2010 - 15h03

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You may have damaged the LEDS.

To drop 4.5 volts with 33 ohm resistor requires a current of 136 mA.
That is 36% more than its maximum rating of 100 mA.

The correct value for 4.5v drop for 50 mA to 75 mA is: 90 ohms to 60 ohms.

A 33 ohm resistor in a series wired LED circuit with a 6 v power supply would have been a current of 45 mA. This is what you probably wanted.

Posted Image
Edited by dewey1 on 07/11/2010 at 17h58.
journeyman68 #6 07/11/2010 - 19h45

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thank you for your help.
i tried still not working, as you say. i think i got bad led..
i order another led from other place. will try when i get new led..
thank you for your help. will let you know when my new led arrive.

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