thanks for the clue, I've just noticed that my super chinese power supply, digital readout, current controlled (price $70), doesn't control the current
with LEDs the history is different: I often see that the most innovative LEDs appear first on ebay, and after some months they are sold by retailers of the big brands
Hero,
when I have to do with a LED of unknown polarity I gently increase the voltage by starting at 1 V and keeping track of the current
I confess, if no light appears I reverse the polarity just for a fraction of time, but I'd like a rule to individuate the polarity
I've noticed that if I read the voltage between the anode and the cathode it is ≈ 70 mV, and that if I reverse the polarity the voltage is ≈ 15 mV: can this constitute a rule?
Hero,
when I have to do with a LED of unknown polarity I gently increase the voltage by starting at 1 V and keeping track of the current
I confess, if no light appears I reverse the polarity just for a fraction of time, but I'd like a rule to individuate the polarity
I've noticed that if I read the voltage between the anode and the cathode it is ≈ 70 mV, and that if I reverse the polarity the voltage is ≈ 15 mV: can this constitute a rule?
Shine a bright light on the diode. It will generate a small voltage in the same polarity as it needs to be connected. (The anode will show the positive voltage.)
A white or blue LED needs a very bright light containing blue or ultraviolet wavelengths (e.g. sunshine or fluorescent) and it will generate a few millivolts and a few microamps.
Hero, the maximum voltage I've applied is 22 V, without damages (current 0.7-0.8 A); at 15 V this LED only starts to glow
sure about the need of resistors? strangely, I've tried the LED from 1 to 22 V by increasing gradually the voltage without current limiters, and it never showed signs of extra current nor of overheating