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Super simple high power LED driver

Picture of Super simple high power LED driver
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This Instructable will show you how to built a Constant Current for high power LEDs, using only two components.

High power LEDs are getting cheaper and cheaper, however the constant current drivers, to drive them are pretty expensive.

Here, I'll show you how to built a simple and cheap, yet very effective constant current source.

The image shows the constant current driver hooked up to a 1W white Luxeon LED.

EDIT: This LED driver supports PWM, which means that you can control the brightness of the LED(s). Those fancy and expensive drivers doesn't support that. I'll post some schematics and applications as soon as i have time.
 
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Step 1: Get the Parts.

Picture of Get the Parts.
Here is a list of the the things you'll need.

a LM317 Regulator.
a Resistor (see next step).
a Heatsink for the LM317 (you don't need one as big as mine, I just took one i had laying around).
some Luxeon, or other brands of high power LEDs (see next step too).
some Wire to hook it up.
it will be a good idea to use a heatsink for the LED as well.
sbuchholz21 month ago

Hi, I'd like to dim this LED (http://www.leds24.com/XcelLED-high-Power-Star-LED-120-bis-160-Lumen-warmweiss) with my Arduino UNO via PWM. It has 350mA and should have 3.2 - 3.4 Volts. How can I do that with my Arduino? I think I'll use the LM350 and a 3.9 Ohm resistor. Or should I rather use the PQ12RD21 because of the 4th Pin? Thank you for your time! :)

shebbron1 month ago

Hi.

Great job. Nice and cheap and easy.
I do have a quick question if i may. If your still taking questions.

Or if anyone else here can help me.

If i was to use several star leds in series, all 1w leds, can they be different forward voltages? Say for instance, i wanted to put a red (2.2-2.6v) and a green (3.2-3.7v) in series, same 1w, 350ma, could you do that? Or would one appear dim from low voltage, or the other burn out from over voltage.

Any advice, however little would be great. Thanks.

tos12349 months ago
Hi there, wonderful guide. I've used it to power some LEDs at 350mA but I am looking to assemble a light using LEDs that require a higher current and just want to ask a few questions to make sure I do it right.

I want to power 8 of these : http://www.ledsupply.com/creexml-w280.php at 2100mA, and I want to run them all plus a 24v fan for cooling from a single 24v power supply, is that possible?

I did the calculation and it looks like I need a resistor that is .6 ohms (do they even make them that small?) to get a 2100mA current from this LM317 regulator.

How many of those LEDs would one driver be able to power? With 24v in I think that would be 6, is that right?

Should I use a different regulator so I can use a resistor that I can actually find?

Would I wire everything in series, with the fan being the first to get power?

How hot do you think these regulators will get?

Any constructive criticism is appreciated as I am a noob with this stuff and it gets a little confusing.






http://english.cxem.net/calc/lm317_calc.php and switch to a LM350T as it can sink more than the LM317 plus it is a drop in replacement.
gizmo1312 months ago
I tried to use this for a 3w led and the only thing that happened was the regulator
got hot.
I first tried to hook it up to 2 3w led's in series then I removed one of them.
Neither time did any of them light up.
I think I need a different regulator. Which one should I use?????
Great aritcle in any case!!!!!!!!!!
gizmo13 gizmo1312 months ago
Forgot to mention the specs of the led's.
forward voltage: 2.9v-3.3v
forward current: 750 mA
hope that helps.
I'm building a bike light version of this running 3 Cree MC-E LEDs, I'm curious if this circuit would run them, also would it interface with a pwm 555 chip if so what would the correct component values be?
santmich1 year ago
another question excuse me for using that resistor 1W LED
santmich1 year ago
hello I congratulate you for what you share only one question in your experience that other component or components you can include it stays cool for both thanks
arashagha1 year ago
hi, if i wanna use 3, 1W leds in series and waNNA connect them to 12-14 volts in my car, what would be the correct R with what Watt??

thx for article
 AI, I am amazed that you are still diligently answering comments two years after you you made your instructable.

I am trying to build this, but I am using two 10w LEDs with a Vf of 3.6 and a current consumption of 2800 mA. For the life of me I can't figure out what regulator to use. Any ideas? 
you have to add a PNP power transistor with IC to incease its current rating.
(Transistor 2N6111 On Heat Sink with LM317 ) 

 

 
 
 
 
 
 
 
 
 
 
you are correct in adding a transistor, but by then ofcourse it is not a ' simple' regulator anymore and it would be better to build a different circuit then, not based on a LM317 because that has a big voltage drop. Use a FET or power transistor with 2 diodes or a simple signal transistor
led-driver5.jpg
Hi Eugenehaller,

could you help me in designing a circuit for lighting 10 w power LED or 1*10 watt leds..

Thanks,

Yugang
Use an LM338 it is rated to 5A.
Hi, sorry for not replying. I must have missed your comment. I have not tried using 10W LEDs with the LM350, but I don't think it's a very good idea, because when I use the LM317 (1500mA max) to drive a LED that just uses 700mA, it gets very hot and needs a pretty big heatsink. This happens because both the LM350 and LM317 are pretty inefficient, so they "burn off" the power as heat. For very high power LEDs, you might be better off with a more efficient regulator. Try the LM1084IT-ADJ. It costs more than the LM350, but it's more efficient and can handle up to 5 Amps. It has the same reference voltage and pinout as the LM350/317, so you can use my instructable with it.
try using a LM350 it is rated at 3 amps or 3000 ma

Lee
hlem4 years ago
Hello AI, Can you give me input on this design here? is it correct? thanks Ha
hlem hlem4 years ago
Artificial Intelligence (author)  hlem4 years ago
Sorry, I can't sse the image. You have to be a registered member to view the image.
Artificial Intelligence (author)  hlem4 years ago
That picture just shows a fish and says "Reef Central".
Sorry, i dont know why linking wont work, but i just found the option here to upload image directly. Also, to add to my question, how efficient is your design?
218872LED.jpg
Artificial Intelligence (author)  hlem4 years ago
Your setup looks fine to me. As far as efficiency goes, I don't know. Remember using heatsinks for your regulators and of course LEDs.
ok thanks, wonder why people would spend $20 or so for a constant current Buck...when they can easily make this for a few $.
Also, since i have 6 in serial, the total voltage drop is 6x3.2(LED)+3(LM) = 22.2V, but my source is 24V, what do i do with the extra 1.8V? same goes for the 6.5A output from the source, my parallel config is only 4.2A (6x700mA), what happen to the other 2.3A?
thanks
Artificial Intelligence (author)  hlem4 years ago
I think, people buy the expensive constant current LED drivers, because they think, it will somehow increase the lifetime of the LED, even though that is not the case. The LM317 will dissipate the 1.8V by turning it into heat. you can use the extra 2.3 Amps to drive more LEDs or other electronics, if you want to.
thanks AI. I was told that the other constant current drivers is more efficient because they waste very little power, using the LM317 in my config will waste over 1W of power. And since there is only 1.8V left, I cant really run more LEDs,
diy_bloke hlem1 year ago
thge effficiency is easy to calculate and thus to compare (though in practice there may be slight variations): if you are using an LED that is say 3 Watt at a forward voltage of 3 Volts and 1 amp current and you are putting in X Volt, well you do the math.
But right off one can already say that when using one 3 Volts LED the efficiency will never be more than 50% (because of the 3 Volt Voltage drop), whereas other circuits claim to have a 70-90% efficiency. For a 3 Volt LED, you would need at least 6Volt input, whereas other circuits will let you use 5 or even 4 Volts input. Ofcourse the efficiency of the LM317 circuit will get better when using more LED's in series it will always at least lose that 3 Volt x LEDcurrent
Artificial Intelligence (author)  hlem4 years ago
Yes you can, because your power supply is capable of delivering 2.3 Amps more than you need and so you can use those excess Amps to power more electronics if you want.
It is extremely inefficient, among the least efficient ways possible to drive an LED.

There is no point to doing it this way. Simply using a series resistor will do just as well, just as efficiently. The only thing nice about this circuit is an easy way to calculate the current regardless of (an unknown mystery LED) what the forward voltage of the LED is.

This doesn't inherently "support PWM" either.

Above all, LM317 is designed to be a voltage regulator. The best way to drive an LED, whether it be by PWM or not, is by more directly regulating the current but ideally, not using a linear voltage drop stage which is what the LM317 is.

It is a good teaching circuit to learn about LM317, but for powering an LED, not so much.

Check out http://www.dealextreme.com as they have a selection of dirt cheap LED drivers for most 1W to 5W applications. And good prices on the most efficient 3W Cree LEDs too.

To put it another way, usign a $4 driver and $6 LED, you would have over triple the light output using less than 1/3rd the power of running this circuit with one LED off more than roughly (too lazy to do the math) 12V, and eliminate the need for a massive heatsink.

LED drivers are purpose designed to do the job best. DIY projects are great but also appreciate when professional EEs pick the right parts, when a factory can get it all made, and delivered to you at a good price ready to do exactly what you need.

Modern tech combined with the internet for finding and ordering products is very very great, even if you want a DIY project there isn't a need to do everything from scratch anymore and with LEDs, to regain the efficiency is very desirable for not only efficiency but to not have to deal with all that heat in a project casing.
tdool1 year ago
Have a few questions on setting this up for my reff tank and possibly simple Dimming ability

OK I want to do a string of 9x 3w LEDs with fv of 3.6v and run them at 700ma.

So if I am understanding I would run them in series add a Power Supply that delivers 35.5volts { (9x3.6)+3 for LM317 }

For R1 I would use a 1.8ohm resister that can take 1amp. is that correct or do I need 5-10amp?

Now if I want to dim it without any fancy PWM circuit can I just add a Pot after R1 to increase resistance which will lower the current in effect dimming the LED's. will this work?? if so what size Pot will I need?

Thanks
tdool tdool1 year ago
I meant 1w or 5-10w resistor not amp sorry
svb931 year ago
hi
i have mobile battery (3.7 volt , 900ma)
Can I plug my battery directly to the 1 watt or 3 watt power led ?
please help me
thanks
spanda51 year ago
http://sevenpanda.com/100w-warm-white-high-power-led-light-lamp-100-watt-p-1415.html#.UFq6bFFfb9Y
spanda51 year ago
I don't know much about of electronics, But I want to recommend you guys some low price LEDs.
http://sevenpanda.com/100w-warm-white-high-power-led-light-lamp-100-watt-p-1415.html#.UFq6bFFfb9Y

http://toyswill.com
vallka1 year ago
Hi all, Just leaning about this stuff and want to try to buld up a nice headlamp or two.
Will this driver work for 3 of this Cree XLamp XR-E Q5 White 3W LED Light Emitter, or should I build one for each like?
http://www.ebay.ca/itm/5PCS-Cree-XLamp-XR-E-Q5-White-3W-LED-Light-Emitter-mounted-20mm-Star-PCB-/320941810262?pt=LH_DefaultDomain_0&hash=item4ab99f6256

I would like to power the 3 with a Ryobi 18V drill battery, I also want to build a couple and power them with 3.7V li-ion (I work with computers and have a pile of 18650 batteries from laptops) so i can put together a few battery sizes.
This is the light design.
http://www.instructables.com/id/Improved-high-power-LED-bike-head-light-with-integ/
PedroDaGr82 years ago
Instead of the LM317, I like to use the Sharp PQ12RD21. It is a four pin voltage regulator, similar in nature to this one but the fourth pin is an on/off pin which can be connected to a PWM for easy dimming. Additionally, because there is a separate pin for PWM dimming, the PWM doesn't need to handle large amounts of current. A simple 555 PWM circuit can do it.
It looks like the PQ12RD21 doesn't have an ADJ pin, and is available as separate models of four voltages. Is that still usable in this application?
I think thats On/Off control terminal , pin 4. When you put a PWM signal in that pin , the output signal (V) response will be almost the same as input , about frequency . So , you'll get PWM signal with high current for dimming LED brightness . If you want to gain more brighness with the same power , this is good way to do.
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HI Team,
Can i use a 12V DC running 3x1w led ?
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