Picture of Super simple high power LED driver
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.

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.
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qasimr11 month ago


i have 3 volt source and 3 volt led with 20 ma current can u help me in designing driver ckt for this led thanx

LostinAsia3 months ago

Good morning kind sir.

I was skeptical that this circuit would work due to it's simplicity.

However, it worked fine and I am quite satisfied.
In the article you mentioned that the circuit supports PMW.

Not sure how to do this, just can't get my head around it. lol

I would like to control the brightness of the LED using PWW from a Arduino Mega.
Not sure how to do this.
Should I just connect the PWW output from Arduino to the ADJ pin?
Thank you in advance.


icskill5 months ago

can you use 1w led driver to power up 3w leds?

martik7775 months ago

CC Led drivers are so cheap on ebay now, less than $1 each, for up to 3 leds, although I've been able to drive 4 from these. There are drivers for 4-5, 8-15 etc for not much more. I have been running these 24x7 for a couple years with no problems.

dröhricht7 months ago

nice tut. maybe when you have time can you make an tut for a 100watt led? oder when cou can help me to tell how i can do it then i made an tut and add inspired by then your nick ,greetz from germany

dröhricht7 months ago

nice tut. maybe when you have time can you make an tut for a 100watt led? oder when cou can help me to tell how i can do it then i made an tut and add inspired by then your nick ,greetz from germany

sango071110 months ago

I have a question about the resistors. I want to drive my 10W LEDs with this. Do the resistors need to be 10W or are 1W Resistors enough? My calculation would be a 1,3ohm Resistor for 900mA at 12V

instruct83910 months ago

this is good driver for led. thanks for sharing

3x1W LED_12.jpg3x3W LED_13V.jpg6x1W LED.jpg6x3W LED.jpg
instruct83910 months ago

this is good driver for led. thanks for sharing

3x1W LED_12.jpg3x3W LED_13V.jpg6x1W LED.jpg6x3W LED.jpg
hlem6 years ago
Hello AI, Can you give me input on this design here? is it correct? thanks Ha
hlem hlem6 years ago
Artificial Intelligence (author)  hlem6 years ago
Sorry, I can't sse the image. You have to be a registered member to view the image.
Artificial Intelligence (author)  hlem6 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?
Artificial Intelligence (author)  hlem6 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.
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.
instruct839 ac-dc10 months ago

Using a resistor also is not a good idea. resistor can make your LED low bright or make life of led shorten because no other component limit the ampere.. i used resistor before and it works good my led light in bar are working for how many years before light is fading. so, that is the difference

mpinner ac-dc1 year ago

i do appreciate diyers and hackers are willing to do whatever takes to get stuff working. efficiency is often a luxury i cannot afford.

thanks for the heads up and cleaning up some of my understanding about the lm317 way of doing things.

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?
Artificial Intelligence (author)  hlem6 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 hlem2 years 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)  hlem6 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.
instruct839 hlem10 months ago

it won't work because you put too much led on your 24V even though it is paralleled. 6 LED with 700mA needs to be.. see this picture i attached.. morethan 24V will work and change your resistor to 1ohms


i think the heat would be problem. and the power loss is big. as the datasheet said the input and output voltage diff must be approx 2-3volt, i think its waste energy. btw its a good idea if the efficiency dont bother you

i'm prefer driving HPL with mosfet and npn transistor, since lm317 have big power loss. in matter of cost efficiency 1 mosfet, 1 npn transistor and 1 limitting resistor would be great. you could make option what type mosfet and npn transistor depend the spec of your HPL. or also you could connect it to PWM (the simple PWM could make with 555 ic, but it could only give you 1A current with 4-15V input0... at least mosfet and npn transistor is the simple way and cheap way to drive HPL in good brightness and good condition

Ploopy1 year ago


sbuchholz21 year 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 year ago


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.

tos12342 years 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.
gizmo132 years 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 gizmo132 years 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?
santmich2 years ago
another question excuse me for using that resistor 1W LED
santmich2 years 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
arashagha2 years 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 ) 


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