The LED is a diode. It will "clamp" to a specific voltage, until its dissipation limits are exceeded. Use something in series to limit the current, and form a voltage divider. Else your high current power supply will be half of the divider :) Thanks, Josh
On Wed, Jul 29, 2020 at 11:23 AM Mauricio Tavares <[email protected]> wrote: > On Wed, Jul 29, 2020 at 11:11 AM Josh Wyatt via TriEmbed > <[email protected]> wrote: > > > > Take a little time and characterize the LED parameters a bit... > > > > I would use a high-ish voltage DC source, like a 12 volt supply, and put > a 100 ohm or so resistor in series with the LED. The resistor will limit > current to 90mA in the worst case (3 volt LED on 12 volt source), and will > allow you to measure the voltage drop across the LED. Once you have that, > use Ohm's law to calculate the current required for "full" rating in > wattage; this might require some guesswork by measuring heat dissipation > with a heatsink, etc. But a safe figure might be 1/2 watt or less for basic > testing. > > > What about those variable voltage power supplies? My crappy one > allows me to set the voltage and then shows how many amps are being > sucked by the circuit. > > > -j > > > > On Wed, Jul 29, 2020 at 10:12 AM Brian via TriEmbed < > [email protected]> wrote: > >> > >> Some tips and educated guesses: > >> > >> This would be a great job for an adjustable benchtop power supply. Set > >> the current limit to something relatively small, say, 100 mA, and start > >> bringing up the voltage until the current limit is hit. Many high-power > >> LEDs like to run at 750 mA, so 100 mA won't be nearly enough power > >> dissipation to worry about overheating them just in the process of > >> finding out the voltage and polarity. You should find a point where > >> current starts increasing rapidly with small increases in voltage, and > >> that'll get you in the ballpark. Then you can set your current limit to > >> 750 mA and turn the voltage all the way up; whatever voltage ends up > >> across the LED at 750 mA is the rated voltage. As others have said, do > >> NOT run these at full power for more than an instant without proper heat > >> sinking. > >> > >> Note that LEDs, being diodes, won't conduct at all until the potential > >> across them exceeds the junction voltage, and that these modules are > >> often individual chips wired in series. If you see 9 chips in there, my > >> guess is that the operational voltage is probably somewhere around 12 V > >> (1.something volts for each junction, which is very reasonable). > >> > >> If you wanted to take a 12-V power supply and just quickly tap the leads > >> one way and then the other, you probably wouldn't toast the module (but > >> you do have more than one, right? ;-) ). You could still put a few > >> hundred ohms in series as ballast if you wanted to be careful. > >> > >> Finally, the "tray" that the silicon sits in is always the cathode, but > >> it looks like you might not be able to see through the cover. It might > >> be a reasonable guess to assume the chassis is the cathode (one lead > >> would be clearly isolated from the rest of the chassis, while the other > >> is not). > >> > >> I take it there are no identifying markings on the device at all? No > >> numbers, codes, anything? > >> > >> HTH, > >> -B > >> > >> > >> _______________________________________________ > >> Triangle, NC Embedded Computing mailing list > >> > >> To post message: [email protected] > >> List info: > http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > >> TriEmbed web site: http://TriEmbed.org > >> To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > >> > > _______________________________________________ > > Triangle, NC Embedded Computing mailing list > > > > To post message: [email protected] > > List info: > http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > > TriEmbed web site: http://TriEmbed.org > > To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > > >
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