Driving LEDs from 12V

Discussion in 'LEDs and Optoelectronics' started by yoyom, Mar 7, 2013.

1. yoyom

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Jan 1, 2013
I need a little help in making a circuit. I have 7 1 WAtt LED and I want to light them up all together from a 12v source. If I connect them in series, 4 will make 12V as they are rated @ 12V 350mA. Cannot series all. And if I make two arrays, one LED will be missing from second array 4+3

If I configure them in parallel and control them with a LM350 @ 2.3A and from a 12V source, will it work without burning the LEDs?

2. BobK

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Jan 5, 2010
I would suggest using two strings and two current sources based on LM317, each providing 350mA.

Are you sure the forward voltage for 4 add up to less then 12V? What color are the LEDs? And what are their specs?

Bob

3. yoyom

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Jan 1, 2013

Ok here in the circuit, we have two CAPS and one end connected to GND, which mean negative terminal of battery, right?

And R2 is again connected to GND. So this means, as per the circuit image, both positive and negative must be connected to these points if I Want to run a LED?

4. yoyom

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Jan 1, 2013
I am using these, as per the spec, its min 3 and max 3.6 v

Like you said 350mA each, but adding 4 leds in a string (series) make around 1.4A current?

5. BobK

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Jan 5, 2010
No, things in series all get the same current, in this case 350mA.

You cannot put 4 in series and drive with 12V since they will take anywhere from 12 to 14.4volts and you will need about 2V extra for the LM317 to operate.

You can buy constant current drivers that will driver all 7 of your LEDs in series.

Bob

6. BobK

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Jan 5, 2010
You said earlier that you got it working. So why are you asking this now?

Also, why do you keep ignoring my advice that you want a current regulator and not a voltage regulator to drive LEDs?

I do not understand your question. The LED would go between the ground and the Out+, but you will need a resistor to limit the current if you insist on using a voltage source instead of a current source.

Bob

Last edited by a moderator: Mar 8, 2013

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Jan 21, 2010
8. yoyom

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Jan 1, 2013
That thread which I posted is just for the sake of my knowledge and not for the LED I am trying to run.

9. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Well, perhaps you can take the opportunity now to tell us *exactly* what you want to achieve.

10. yoyom

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Jan 1, 2013
In the new thread, I just wanted to understand the circuit diagram, I had no intention of making it. But in the original thread, I want to know how do I drive my LEDs. SImple.

So I guess its clear now. Now, please tell me, like Bob said, I should go for Constant Currnt rather Constant Voltage, if I assemble my LEDs in series and configure LM317 for 350mA, does it mean, to drive all the LEDs it will ONLY draw 350mA or it will draw 7(LEDs) x 350mA = 2.45A?

11. BobK

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Jan 5, 2010
As I stated before, with 12V you can only put a max of 3 in series. This string would use 350mA. For seven all together, you only choce is 3 regulators with 3, 2, and 2 LEDs. Each one would be regulated at 350mA. Or, if you could go to a higher voltage, say 28V, you could put all 7 is series and have one regulator at 350mA.

Bob

12. yoyom

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Jan 1, 2013
Alrito. Thanx ! This means if I use a battery of say 50Ah, that battery should die after approx 142hrs at total 100% drain?

(50/.35)

13. BobK

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Jan 5, 2010
Not if you are using 3 strings at 350mA, that would be 1/3 what you have calculated.

Bob

14. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
You didn't start a new thread. I have moved all the posts that I think are about something new to this new thread from here.

15. yoyom

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Jan 1, 2013
You mean 47 hours?

16. BobK

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Jan 5, 2010
Yep. The currents in a parallel circuit add. 3 strings of LEDs drawing 350 mA is drawing 1005 mA altogether.

Bob

17. yoyom

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Jan 1, 2013
I m sorry for my little knowledge. You said I should configure LM317 to allow on 350mA in constant current mode, then how will it will be able to provide 1050mA?

18. BobK

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Jan 5, 2010
I said to use 3 of them, one for each string of LEDs.

Bob