[TriEmbed] A little help

Kevin McClaning mcckevin at mcclaning.com
Wed Jul 29 11:03:28 CDT 2020


I use Brian's method all the time when driving LEDs or electromagnets. 
The current limit feature on most power supplies is often overlooked, 
but very useful.

K

On 7/29/20 10:05 AM, Brian via TriEmbed 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
>
>
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