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Testing LED's

spike1947

Feb 4, 2016
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Feb 4, 2016
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Hi
I am trying to replace some dead LED's on a couple of strips from a LED TV, tested a row of 4 using 12.2 v dc and it shows 2 working, now I am trying test a single LED using 3.23 v dc ( 2xAAA Bats ) , but even the good ones are not lighting with that voltage, what am I doing wrong here !.
attached pics showing 2 LED's lit with a supply to the strip of 12.2 v dc.
 

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Harald Kapp

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Nov 17, 2011
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I wouldn't know what size resistor to use !
Depends on the voltage source, the LED and the current.
Use 3 × 1.5 V batteries = 4.5 V. Assume ~ 3 V for the white LED and 10 mA then R = (4.5 V - 3 V) / 0.01 A = 150 Ω.
The exact value is not critical. anything between 100 Ω and 220 Ω will work, even 300 Ω should work.
2 × 1.5 V batteries may not be enough to power the LEDs. White LEDs can have > 3 V pass voltage (the good point here is that you will not have destroyed these LEDs with the 3 V from the batteries :)).

You also need to observe the polarity. LEDs light up only with anode to '+' and cathode to '-'. But of course you are aware of this, aren't you?
 
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