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Got a question about driving LEDs? (Another work in progress)

CocaCola

Apr 7, 2012
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Im still a little confused about one thing though. I need to run and LED off 120v wall power.

Can you elaborate further, how many LEDs the purpose and so on?

As always when working with mains you have to understand you are dealing with potentially lethal power levels... With that said most of the time you will find the best way to run LEDs off of the mains is to use a wall wart (aka power adapter) to drop the voltage down to a much lower and safe level to play with... But, that is not to say it's the only way to do it...
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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You should be able to drive each one at 20mA. Yes a resistor in each cathode.
 

donkey

Feb 26, 2011
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trying to get specs or data sheet of the seller. but at 12v is that the recommended resistor value?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Around 500 ohms. Say 470 for blue and 560 for red and green.
 

donkey

Feb 26, 2011
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Ok so what voltage and resistor? am on phone so spelling may be off. am looking at max 9v but min wil be 3.3v or less if i use a diode
 

Discofmj

Aug 17, 2012
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Would it be possible to have input from a stereo system connected to a digital color organ so the variation of the intensity of the music will correspond to a different array of LED's?
 

virtual1

Mar 29, 2012
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fyi high current drivers cheap on ebay

I just picked up 10 of these for playing with. I wanted to attach a 2 D cell light to my bicycle, and run it off the 12v battery in the pack. The light is probably just using the cell resistance to limit current, so 12v source would be bad. I didn't want to use a linear regulator since there was going to be a very large voltage drop required (12v down to about 2.7v) that would not only heat up the regulator but also severely shorten my battery life.

I found these "buck-down" regulators on ebay. There are several variations on them, some that are voltage regulators, some that are current, some that do both. This one just does current, which is really what you need to power a higher output LED like those in the 1-3 watt range.

http://www.ebay.com/itm/251066005460

He's selling them for a buck sixty (+free ship) which is hard to beat for what it does. I've installed the regulator in where the D batteries were and it's working really well. Buck-down regulation is a very efficient way to limit current to LEDs, so the regulator doesn't get past skin temp warm when passing an amp at 2.7 volts. There's a multiturn pot on the board to dial up the current. It's well-regulated as long as the output resistance doesn't change, which shouldn't be an issue for driving an LED. The only problem I've ran into is there's a good deal of switching noise. This regulator ships with a 220uF on the input and output, but nothing smaller. There are pads on both ends however where a SMC could go, I will try adding 0.01uF on both ends and see if that keeps the noise out of the 2m radio that's also on the bike. (running on the same 12v battery, but the noise is NOT coming in through the DC, it's radiating and picking up on the antenna)
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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If a comparison chart exists it would be nice to have a link in the categories section in post 1. I'm referring to a link maintaining a running chart of available LEDs containing basic specs like Vfd, Ifd (Cont), Lumens, etc.

Chris
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Sure, if you can put something together or find a link to the available information, I will add it.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Unfortunately I don't know of any. I think Digikey's product filters come close though.

Chris
 

ektel

Jan 12, 2013
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a concise book on led, it would take hours to find this type of short and important info
 

farhan007

Jan 19, 2013
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steve

Awesome bit of information steve. Thanks a lot for such a detailed explanation. It will surely go a long way for me to understand the concept and its application in a much better way......
 

morphingstar

Mar 1, 2012
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LED rotating lights current load definition

Hi, I found a current driver for LED. In the specifications I found a 10% load calculation which I do not truly understand.
Here is the extract of vendor's definition:
Revolving light current: constant current value * (1% -100%), Revolving light current value Linkage with the constant current value, such as the constant current value is 3A, Revolving light current is set to constant current of 0.1 times (0.1 * 3A = 0.3A) when adjusted to the constant current value when the 2A, then Revolving light current is 0.2A (0.1 * 2A = 0.2A). Default 0.1 times

Here is what I asked the vendor, not getting an answer so far.
please clarify for me the term "revolving light current". To what sort of light does this refer? Is it an intermittent pulsed load or what. Give example link. I want to make sure not ordering what I can not use.
There seems to be a "10% of a value". Does this mean the maximum (peak) current may not be more than the specified current for the LED, even if the average current is much lower, e.g. 10%. (10% load time, 90 % pause time. Is this what it is?


My search for Revolving Lights brought no answers as to load behavior.

There are several LED driver supplier stating similar specifications for their LED drivers. Among them this Revolving Light seems to be a standard definition. Buck convertor term shows up often.

links:
[LED driver]
http://www.aliexpress.com/item/20-P...Step-Down-Converter-LED-Driver/718018498.html
http://www.aliexpress.com/item/free...-constant-current-power-supply/662994428.html
http://www.aliexpress.com/item/DC-D...module-with-charging-indicator/538637674.html
http://www.aliexpress.com/item/Free...rter-LED-Driver-Module-Charger/615480671.html
http://www.aliexpress.com/item/Free...rrent-Power-Supply-Module-with/651705774.html
http://www.aliexpress.com/item/Adju...power-supply-module-with-CC-CV/697586932.html
http://www.aliexpress.com/item/DC-D...Battery-Charger-Module-4-5-35V/553413307.html
http://www.aliexpress.com/item/5-PC...7-35V-Output-1-25-25V-0-3A-LED/730918140.html
 
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