## Step 3: Assemble It

I couldn't get my schematic drawing program to work, so here is a hand drawn.

The constant current source has a drop voltage of 3 V, so the supply voltage should always be 3 V higher than the LED voltage and can be up to 37V which is the maximum input voltage of the LM317.

Example: You are going to connect two white Luxeon LEDs with 3,42 forward voltage each (mostly mentioned as Vf in common datasheets). The input voltage can change from 9,84V (3,42 + 3,42 + 3) till 37V (3,42 + 3,42 + 30,6).

You can connect up to ten high power LEDs to this circuit.

The higher voltage you supply the LM317 with, the hotter it gets. so it wont be a good idea to supply it with unnecessary high voltage.
<p>Input voltage ?</p>
<p>why cant u put dot(.) instead of comma(,)<br>it makes little confusing.... :/</p>
<p>Why cant you look at the comma and see a dot?</p>
<p>In Europe they use a dot where a comma would go, and a comma where a dot would go. Just accept that and change it accordingly when you make your own plans.</p>
<p>Yup, low value resistor+lots of current = lots of power (heat) loss. Switching is the way to go. If you get creative, the power loss in the driver circuit can be cut down to almost nothing. A switched diode / capacitor combination would work quite well.</p>
<p>this circuit is a nonsense. </p><p>using a high power resistor is a proof of very poor efficiency !. Most of energy is used to produce HOT in the R.</p><p>switching regulator is the right way... </p><p>NCP3065 just a little bit more complex</p><p>http://www.onsemi.com/pub_link/Collateral/NCP3065.PDF</p>
<p>can you suggest the <strong>other</strong> regulator ICs for the same job ()? i need to drive a typical 5W power LED at maximum efficiency as a strobe.</p><p><br>Regards and Thanks.</p>
<p>i made it, the wire melted, it's overheat</p>
Where would I hook up the pot meter as in where do the pot meter wires go please help me out thanks
<p>buen dia</p><p>me podrian dar el cricuito para conectar un led de 50w para 12v usando lm317</p><p>saludos</p>
<p>Good morning kind sir.</p><p>I was skeptical that this circuit would work due to it's simplicity.</p><p>However, it worked fine and I am quite satisfied.<br>In the article you mentioned that the circuit supports PMW.</p><p>Not sure how to do this, just can't get my head around it. lol</p><p>I would like to control the brightness of the LED using PWW from a Arduino Mega.<br>Not sure how to do this.<br>Should I just connect the PWW output from Arduino to the ADJ pin?<br>Thank you in advance.</p><p>Charlie</p>
<p>If I were doing I would probably use a P channel FET to switch the VIN signal or a N channel FET to switch the LED Cathode pin. Either should work. Make sure the FET is a logic level type FET so you can switch it on/off correctly with Arduino voltages. Also make sure the FET can handle the LED current.</p>
<p>hy </p><p> 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</p>
<p>You need a 1 Ohm 1/8W resistor in series to give you 20mA. Type LED calculator into google and the top link is useful.</p>
<p>I like how simple this is. Probably not that efficient as a lot of energy will be wasted on heating up the LM317 device but still a good job.</p>
<p>can you use 1w led driver to power up 3w leds?</p>
<p>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. </p>
<p>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</p>
<p>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</p>
<p>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</p>
<p>this is good driver for led. thanks for sharing</p>
<p>this is good driver for led. thanks for sharing</p>
Hello AI, Can you give me input on this design here? is it correct? thanks Ha
sorry, here is the image link <a rel="nofollow" href="http://reefcentral.com/gallery/showphoto.php?photo=275324&papass=&sort=1&thecat=">http://reefcentral.com/gallery/showphoto.php?photo=275324&amp;papass=&amp;sort=1&amp;thecat=</a><br/>
Sorry, I can't sse the image. You have to be a registered member to view the image.
oh sorry, here is the direct link. <a rel="nofollow" href="http://reefcentral.com/gallery/data/500/218872LED.jpg">http://reefcentral.com/gallery/data/500/218872LED.jpg</a><br/>
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?
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.<br/><br/>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.<br/><br/>This doesn't inherently &quot;support PWM&quot; either.<br/><br/>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.<br/><br/>It is a good teaching circuit to learn about LM317, but for powering an LED, not so much.<br/><br/>Check out <a rel="nofollow" href="http://www.dealextreme.com">http://www.dealextreme.com</a> 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.<br/><br/>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.<br/><br/>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. <br/><br/>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.<br/>
<p>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</p>
<p>i do appreciate diyers and hackers are willing to do whatever takes to get stuff working. efficiency is often a luxury i cannot afford. </p><p>thanks for the heads up and cleaning up some of my understanding about the lm317 way of doing things. </p>
ok thanks, wonder why people would spend \$20 or so for a constant current Buck...when they can easily make this for a few \$.<br/>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?<br/>thanks<br/>
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,
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. <br>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
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.
<p>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</p>
<p>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</p>
<p>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</p>
<p>Cool!</p>
<p>Hi, I'd like to dim this LED (<a href="http://www.leds24.com/XcelLED-high-Power-Star-LED-120-bis-160-Lumen-warmweiss" rel="nofollow">http://www.leds24.com/XcelLED-high-Power-Star-LED-120-bis-160-Lumen-warmweiss</a>) 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! :)</p>
<p>Hi.</p><p>Great job. Nice and cheap and easy.<br>I do have a quick question if i may. If your still taking questions.</p><p>Or if anyone else here can help me.</p><p>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.</p><p>Any advice, however little would be great. Thanks.</p>
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. <br> <br>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? <br> <br>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. <br> <br>How many of those LEDs would one driver be able to power? With 24v in I think that would be 6, is that right? <br> <br>Should I use a different regulator so I can use a resistor that I can actually find? <br> <br>Would I wire everything in series, with the fan being the first to get power? <br> <br>How hot do you think these regulators will get? <br> <br>Any constructive criticism is appreciated as I am a noob with this stuff and it gets a little confusing. <br> <br> <br> <br> <br> <br> <br>
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.
I tried to use this for a 3w led and the only thing that happened was the regulator <br>got hot. <br>I first tried to hook it up to 2 3w led's in series then I removed one of them. <br>Neither time did any of them light up. <br>I think I need a different regulator. Which one should I use????? <br>Great aritcle in any case!!!!!!!!!!
Forgot to mention the specs of the led's. <br>forward voltage: 2.9v-3.3v <br>forward current: 750 mA <br>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?
another question excuse me for using that resistor 1W LED
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