Maker Pro
Got a question about driving LEDs?

Got a question about driving LEDs?

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
(*steve*) submitted a new resource:

Got a question about driving LEDs? - A list of common answers and links to useful documentation on driving LEDs.

OK, lots of people ask questions about driving LEDs. So here's a list of common answers and pointers to documentation that is useful.

Here's what I'm covering:

0) Why LEDs are different from light bulbs
0.5) Voltage and current sources
1) Driving a single low power LED
2) Driving a large array of low power LEDs (Including a practical example)
3) Driving a single high power LED <-- Constant current sources are discussed here!
4) Driving an array of high power LEDs
5) LED Lifetime <-- new
6)...

Read more about this resource...
 
Last edited by a moderator:

chopnhack

Apr 28, 2014
1,576
Joined
Apr 28, 2014
Messages
1,576
Awesome Steve!! Typo under caption of 1.1 : I think you meant it's <<This uses Vs and Vl instead of V and Vf, but it'd just alternative labelling.>>
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
That's a resource from the old version of Electronics Point (with different software). It was converted over but some formatting didn't quite come across.

I have been promising myself to get in and fix it for some time. Perhaps you have given me extra incentive :)
 

chopnhack

Apr 28, 2014
1,576
Joined
Apr 28, 2014
Messages
1,576
That's a resource from the old version of Electronics Point (with different software). It was converted over but some formatting didn't quite come across.

I have been promising myself to get in and fix it for some time. Perhaps you have given me extra incentive :)

Old or not, I found it most enlightening ;-) It may raise more questions and I am more than happy to proof read it. Thanks for taking the time to upload it and continuing to answer questions.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
It looks like that's in better shape than I thought it was (perhaps Ian fixed it for me?)

Anyway, I've incorporated the fix for the typo you spotted and a couple of other very minor issues.
 

Jeff Nevil

Sep 15, 2015
4
Joined
Sep 15, 2015
Messages
4
This is excellent, thanks for posting, answered the questions I had and ones that I hadn't even thought of yet!

Jeff
 

JoeM

Sep 5, 2014
33
Joined
Sep 5, 2014
Messages
33
Loved it.

One comment on LED Christmas lights. They do fail over time, but the reasons vary according to the manufacturer, and the quality of the lights. We got tired of replacing our lights every year, so we researched commercial LED Christmas lights. So far the lights we bought have worked for three years with no failures. One reason is that the LED bulbs are sealed, and not removable. They are water proof, and not being in a socket, there is no possibility of corrosion. Standard LED Christmas lights almost always fail because of corrosion in the socket. Water intrusion speeds that process considerably, but even without water, the corrosion sets in and eventually leads to failure. So to get good LED Christmas lights, fist the design has to be a good one, then the parts used need to be of high quality, then the construction has to be sealed from outside contaminants.
LED's would be really expensive if the leads were made from solid copper, as suh, the leads are made of steal, and have a very thin copper plating. It only takes a little moisture to start the corrosion process, and that happens at a different rate for each bulb. So that explains how we can take bulbs out of the socket, wipe it off and possibly get our lights from last year to work for another year. Each year it gets harder and harder to fix the lights until we get frustrated and buy new. Then the process starts over.

That all ended when we bought the commercial LED lights, we can't unplug the bulbs, but because of that, there is no reason to unplug the bulbs.

This year, I needed some twinkle LED'S for a 4 foot star that I put up on a 40 foot tower on my house. We got the trickle LED'S at Home Depot, and they failed before the end of the first season. The box they came in said they had a warranty on them, so they went back to Home Depot and we got a full refund.

I hope some of this will enlighten someone who is getting tired of buying new lights every year.

Joe
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
That is an interesting circuit. It seems to have a relatively low impedance for a constant current source. But given that it can operate from a very low supply rail I'm pretty impressed.

I am actually looking for a constant current source (or a voltage regulator) which can run from one or two AA cells to provide between 1 and 1.4V or 11 and 14mA to a load. (note that I want to adjust it in that range, not merely keep it within those limits).
 

bertus

Moderator
Nov 8, 2019
3,348
Joined
Nov 8, 2019
Messages
3,348
Hello,

Perhaps a little addition to your resource.
The different colors of leds will have different forward voltages:

IV-curves-all-colours.png

Led_color_chart.png

Also a note on the different ciruits for leds in the attached PDF.

Bertus
 

Attachments

  • Comparison_of_LED_circuits.pdf
    87.1 KB · Views: 8
Top