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Old 9th December 2004, 05:32 AM   (permalink)
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Hi Ms,
You like using a 60 ohm current-limiting resistor for a LED with a 9V supply, dontcha?
A common red LED has about a 2V drop and a 30mA to 50mA absolute maximum continuous current rating. With a 60 ohm current-limiting resistor and a 9V supply, it would draw 117mA and will melt or surely burn-out!
Even an "ultra-bright" blue or white LED with a 3.5V drop would draw 92mA! For a few milliseconds it would look like a searchlight before it burned-out. But you would be blinded and won't see the smoke.
For an indicator light only about 10mA is needed which would use a 700 ohm (use a standard 680 ohm) current-limiting resistor (for a common red LED) with a 9V supply.
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