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Topic: Led resistor calculator help (Read 3 times) previous topic - next topic

liudr


The 0.5w power rating is a maximum allowable value.  You wouldn't want to operate at that value.

Don

Yes, yes, my point was also "only ~= 0.5W and stop" (that's when the OP trusts the 0.5W so maybe while ramping voltage the LED pops at a lower value then good luck trying to be a QC/testing engineer) :)

floresta

You really don't have to 'test' anything.  You just keep the current below it's maximum rated value and the power will automatically be less than the maximum rated value.  The only reason to be at all concerned with the forward voltage is (1) to make sure your supply is greater than this value, and (2) to have a ballpark value from which to start calculating the series resistor.

Don

liudr

The OP doesn't have either the current rating or forward voltage and a 0.5w was all that the OP knows. So to make an estimate of both forward voltage and current rating from the 0.5W, I suggest the ramping voltage.

Grumpy_Mike

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and (2) to have a ballpark value from which to start calculating the series resistor.

It's a high power LED you DON'T use a resistor with these.

adilmalik

got them working,with a resistor ,and they dont heat up, the problem was that the two same type of led ,were different but they looked same; one type required 145ma and the other type 30-40ma, so i fixed a pot and got the 30-40ma one working perfectly, the voltage drop i measured was 3.10v and the current was 35ma,with a resistor of around 81 ohm.

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