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 > _______________________________________________ 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
