http://www.instructables.com/id/Super-simple-high-power-LED-driver/

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Super simple high power LED driverby Artificial Intelligence on March 19, 2008

Table of Contents

Super simple high power LED driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro: Super simple high power LED driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1: Get the Parts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 2: How it works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 3: Assemble it . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

Author:Artificial IntelligenceHi all, I'm a college student in the copenhagen technical college. I'm currently working with 3D printers and I'm building my own RepRap.

Intro: Super simple high power LED driverThis 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 postsome schematics and applications as soon as i have time.

Step 1: 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.

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

Step 2: How it worksThe LM317 regulator gives out a constant voltage of 1,25 volts between ADJ and Vout, so by adding a resistor between these two outputs, you'll get a constant current.

Ohm's law says that U/I=R, which means that Voltage divided by Ampere makes resistance.

so if you want to connect one or more luxeon 1W LEDs, which has a power consumption of 350mA, the calculation should look like this: 1,25 (the constant referencevoltage of the LM317) divided by 0,350 (the LEDs power consumption) makes 3,57. So if the resistor is 3,57, constant current will be 350mA. The closest E12 value is 3,9ohms, it will give you a constant current of 321mA. However you can't see any difference in the light output.

If you use 3W LEDs, which has a current consumption of 700mA, the calculation should be: 1,25 divided by 0,7 makes 1,78. The closest E12 value is 1,8 ohms, theoutput will be 694mA

the resistor must be at least 1W in both calculations.

Although the LM317 is rated for 1,5 Ampere, I wouldn't recommend it for applications that need more than 1 Amperes, because it gets very, VERY hot. the LM350 isequal to the LM317, but it's rated for 3 Amps

Step 3: Assemble itI 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 themaximum 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 canchange 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.

Image Notes1. To plus of the LED(s)2. + from power supply.

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

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Comments

50 comments Add Comment view all 229 comments

Jkirk3279 says: Feb 5, 2011. 10:38 AM REPLYHi.

I've been studying this subject.

This regulator seems just what I'm looking for. Not tuned in yet on the "constant current" concept though.

I want to drive twenty 1 watt LED's in series. Each uses 2.79 volts and 350 mA.

So if I drove them in parallel I'd need 2.79v but a staggering 7 amps !

I asked an electronics teacher and he said "run them in series".

So then you need 28 volts but only 350 mA for 20 watts, plus a balancing resistor.

Very little power wasted.

As I understand it each LED sees 350mA, but the voltage pressure drops progressively until finally it hits the resistor.

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

mjhilger says: Feb 22, 2011. 3:56 PM REPLYThe voltage drop across any LED is dependent on the junction temprature. The temp will rise as they are driven in higher power. And, the voltagechange between dim and fully bright is small (compared to the drive voltage). However the current to light output is relatively consistent. One should driveLED's via current to protect longevity and operation. Because each LED of the same part number, from the same manufacturer batch will vary its exactvoltage per current, you cannot run LED's in parallel; there is no way to regulate the current to each in this manner. So you must drive them in series tomaintain control to drive near peak output.The constant current concept is a consistent way to safely drive power through the LED's one or many. You are correct the voltage goes up on yoursupply demands, but the constant current (or current regulator) provides the proper power control.Hope that helps to explain constant current concept

TheNuclearWatermelon says: Feb 13, 2011. 8:22 AM REPLYUgh! The LM317 is the most common current regulator circuit ever! I hate it's 3v dropout! Why can't anyone show us a simple boost circuit like the LM3410?

aekara says: Jan 27, 2011. 11:33 PM REPLYi need help of powering a 30w high power led

THE LEDhttp://cgi.ebay.com/30W-White-High-Power-2100LM-LED-Light-Lamp-Bulb-A_W0QQitemZ220708010099QQcategoryZ163866QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D10%26pmod%3D220693236934%26ps%3D63%26clkid%3D5621333683761900258

CAN I USE THE LM317 OR I NEED A DIFIRENT VOLTAGE REGULATOR

THE INPUT POWER WILL BE 16V

macnomad84 says: Feb 9, 2011. 10:31 AM REPLYDATA SHEEThttp://www.national.com/ds/LM/LM117.pdf

"The LM117 series of adjustable 3-terminal positive voltageregulators is capable of supplying in excess of 1.5A over a1.2V to 37V output range."

P = V * I = 16 Volts * 1.5 Amp = 40 W

I think you can. Go for it. Someone correct me if I'm wrong. Gonna keep reading this DS...

ovven says: Jan 7, 2011. 9:48 AM REPLYGreat guide, really useful. I am trying to rig up a system of 11 high power LEDs, with a forward current of 350 mA and a forward Voltage averaging 3.5 V.would it be best to run these all with different drivers or all in series or a mixture and also what would be the best regulator for the system. I'm nearly at thepoint of comprehending all of this but thats not the same as understandingit to a competant enough level to make it, just yet.

Cheers

morphious69 says: Nov 29, 2010. 10:41 PM REPLYhi. I am wondering if you could use a couple of these for higher power like what is consumed by the 10 watt or higher LEDs? can they be adjusted to put outthe higher voltages needed like 12 or 24 volts and just be expected to supply the amount of amperage they can handle but multiply this by having several ofthem in parallel so as to add more amps?

Electroinnovation says: Nov 12, 2010. 5:09 PM REPLYCould this handle 2 1W white leds? and if so would i put them in a parallel or a series circuit?

LEDismylife says: Oct 2, 2010. 3:21 AM REPLYTo anyone who knows, how can I extend my LED output from 700mA to 1000mA? should i change just the regulator?

eugenehaller says: Feb 3, 2010. 12:22 PM REPLY 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 whatregulator to use. Any ideas?

valveman says: Sep 9, 2010. 1:55 PM REPLYUse an LM338 it is rated to 5A.

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

seethasub says: Mar 11, 2010. 1:40 AM REPLYyou have to add a PNP power transistor with IC to incease its current rating.(Transistor 2N6111 On Heat Sink with LM317 )

Artificial Intelligence says: Mar 2, 2010. 7:20 AM REPLYHi, 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 happensbecause 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 amore 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 samereference voltage and pinout as the LM350/317, so you can use my instructable with it.

doransignal says: Mar 1, 2010. 3:01 PM REPLYtry using a LM350 it is rated at 3 amps or 3000 ma

Lee

oli1122 says: Sep 9, 2010. 8:46 AM REPLYCould i do this for a 10W Led of 1000ma???

SRWitt says: Sep 7, 2010. 8:12 PM REPLYLets see if you're still answering questions. So I'm building an array of 3w Leds in red, yellow, and blue.

I'm planning on using the LM1084it-adj vs the LM317.

So far I've figured based on datasheets @ 700ma, I should have about 2v total drop with the 1084 (1.25adj+ ~.8@700mA). Is this correct?

My source is going to be a computer PSU converted to a benchtop PSU, using the 12V out. Based on my LED's datasheets, I should be at about 2.2V perRed or Yellow @700ma, based on this, the 1084 will be dissipating 1.2V@700mA with 4 red or yellow LEDs wired in series (total of .84W). For the blue I'vefigured ~3.6V for 700mA, with 2 in series the 1084 would have to drop ~2.8V@700ma (1.96W).

Forgive me, I am a relative newb to electronics, does my math seem correct? Am I misinterpreting the datasheets when it comes to how much voltage the1084 drops under varying loads?

peterbeihoffer says: Aug 22, 2010. 1:45 AM REPLYHi I need some help. I am trying to design a high powered LED light. I want to put together 10X 1W high power LEDs. I was thinking of using 10 topledlight #BY1W-WH they have a DC Forward Voltage (VF): 3.0V ~ 3.8V, and a DC Forward Current (IF): 350mA ~ 400mA. I was wondering what the simplest andeasiest way to wire this. Could I just use 1 10w driver? any help or tips would be much appreciated. Thanks

WingmanSVT says: Aug 8, 2010. 5:44 PM REPLYIm a bit confused about using this circuit with LEDs wired in series. I have 2, 3 watt LEDs wired in series, each has a forward voltage of 3.8 max and 700 ma.What resistor would i need to have between pin 2 and 3 on the LM317?

jon1888 says: Jul 17, 2010. 4:02 PM REPLYdoes anyone know what it would take to power a 50w 24v-26v

TheWhatnought says: Jun 30, 2010. 1:12 AM REPLYHey, is this usable for some of the really high current emitters? I'm trying to find a cheap, only on/off CC driver for a 3.86V 2800mA LED. I'm also trying todrive it off of a 12VDC supply. Any suggestions?

pedroalaray says: May 22, 2010. 10:00 AM REPLYHi could you take a look at this circuit I've planned out? I think it would work but not sure if I should order the bits thank you Peter

http://farm4.static.flickr.com/3339/4629373728_186cbc5e3f_o.jpg

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

Joshus says: Jun 11, 2009. 10:32 PM REPLYHi, I have been messing with DC power supplies for some time. Can I just use a bridge rectifier with my 110V ac at home followed by your design? Howcould I acomplish this? Thank you so much for all of the information! Reading your instructable and answers to questions has helped me ALOT!

Rusdy says: Jan 3, 2010. 9:47 PM REPLY After many googling and forums, I've found this inexpensive current source, with wide AC inputs (110-240VAC). Link is here

(If the link doesn't work, just type "current source" on the linked website, www.dealextreme.com, and browse for the correct input voltage)

I just received it today, so haven't managed to tried it myself, but googling the driver's datasheet (AP3706), definitely a true current source! The productis rated to 350mA, but if you're good with electronics, you can change the Rsense (which I only can guess at the moment which one on board) to suit

lightartist1 says: Apr 30, 2010. 6:03 PM REPLY hey rusdy , i came across your comment while researching powering a led 'star'. i have a couple of questions: how are the drivers from deal extremeworking out for you? also, what type of power rated wall wart would i need to power just one star safely? there are good deals on surplus sites forwall warts, i just want the type that would complement the 350 mA star as cheaply as possible. thanks!

Rusdy says: May 1, 2010. 6:03 AM REPLYI believe this one (I linked above from DealExtreme) will be the best option for powering a single white LED. Simple, cheap, and really small. Justnote that there are 2 types of driver offered: 350mA and 700mA option, so they need to be matched with your LED (or else the driver can fry yourLED!)

Also note that this driver only have max output voltage of around 4V, so only good for powering a single white LED. Obviously, you have to becomfortable with the hand skill for installing such a small driver (with live voltage!). Hope that helps...

lightartist1 says: May 1, 2010. 7:34 PM REPLY hey rusdy. thanks for your promt reply. i appreciate the info very much.

Artificial Intelligence says: Jan 4, 2010. 5:53 AM REPLYI have that exact same driver, and it works quite well, and its very compact. Doesn't appear to support PWM from an external source though.

Artificial Intelligence says: Jun 12, 2009. 11:44 AM REPLYUnfortunately, the maximal input voltage of the LM317 is 37V, so hooking it up to mains voltage wouldn't be a good idea. There are two things, you cando. 1. connect it to a wall wart adapter or another DC supply, that puts out less than 37 Volts. 2. Buy a preassembled LED Constant current Powersupply that runs directly on mains power, like the ones they sell at dealextreme. Their website is currently down, so I can't post a link.

tkjtkj says: Aug 21, 2010. 6:41 AM REPLYmy intended voltage source varies from 32v to 41.3 .. i wonder if that high limit would destroy the regulator .. or is the referenced 3amp regulatorperhaps more tolerant of applied voltages a lil above its specified max ?? tkjtkj@gmail.com

Joshus says: Sep 21, 2009. 12:17 AM REPLYWhat if I took a bridge rectifier from 110VAC followed by several LM317 regulators in parellel. Each LM317 would "feel" a reduced voltage right?

Artificial Intelligence says: Sep 23, 2009. 1:40 PM REPLYWell. If they are connected in parallel, they will all take the 110V and you will be letting out some of that magical blue smoke. They will most likelyexplode.

cdousley says: Jul 28, 2010. 10:43 PM REPLYblue?

Joshus says: Jun 13, 2009. 2:00 AM REPLYCould I just us a transformer to reduce the ac voltage to a smaller value, then us a bridge rectifier follower by the voltage ragulator and resistor?

Artificial Intelligence says: Jun 13, 2009. 2:35 AM REPLYYes you can.

aleysth says: Apr 27, 2010. 11:39 PM REPLYhi, can this circuit use to power a Bridgelux LED ARRAY, BXRA-C0400-00000? voltage = 10.6, constant current 600mA, Power = 6.4w.

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

jfenwick says: Apr 13, 2010. 8:37 PM REPLYI'm confused about how the voltage regulator behaves with only one resistor.The voltage of the LM317 can usually be modified by changing the ratio of the two resistors going into ADJ and Vout.This is usually based on the equation Vout = 1.25(1 + R2/R1).If R1 = R2, then doesn't the equation give you 1.25(1 + 1) = 1.25 * 2 = 2.50V?If that's the case, I would think your computation for how to determine what resistor you need for limiting current would come out differently.For instance, when you have a 1W LED, which requires 350 mA, you use Ohm's Law to come up with 1.25/0.350 = 3.57.Wouldn't you instead end up with 2.50/0.350 = 7.14?

jfenwick says: Apr 13, 2010. 8:39 PM REPLYThe last two lines were a mistake.I'm having a hard time understanding how you can even use Ohm's Law here since any time you change your resistor, you're going to change how muchvoltage you're getting because you'll be changing the voltage going to the ADJ pin.

cdousley says: Apr 8, 2010. 3:36 PM REPLYwould this work for a laser ? if it does what would i have to do to get about 4vand 30 millamps

vinet says: Mar 19, 2010. 1:04 AM REPLYThanks AI I got the LEDs up and running with 12v power supply. Thank you once again for all your replies. Soon I will post an instructable about theheadlights.

vinet says: Mar 14, 2010. 11:52 PM REPLYI am about to use this circuit and 3 LEDs in a motorcycle headlight. So the input voltage could be at around 12v to 14v. Is so much voltage sufficient to drivethe LEDs. By the way I have not tested the circuit with the LEDs. I have only tested the circuit using a multimeter and with an input voltage of 9v.

vinet says: Mar 14, 2010. 10:47 AM REPLYThanks AI your circuit works. I measured it using a multimeter. It read 310mah. I used it with a 9v battery. The voltage was 8.38v. Is this much voltage andcurrent ok for using 3pcs of 1watt LED?

Artificial Intelligence says: Mar 14, 2010. 2:14 PM REPLY Did you test the circuit with 3 LEDs at 9 Volts??? If you use white LEDs, the LED voltage is likely around 3.5V, so 3.5*3=10.5 + 3 Volts dropout from theregulator is 13.5, so you'll want a voltage of at least 13.5Volts, however you can usually go a little less than one volt lower than that, so you might get it towork successfully down to around 12.5 volts.

vinet says: Mar 14, 2010. 5:40 AM REPLYAlso AI for a 1watt LED is 3.9ohms resistor OK.

vinet says: Mar 14, 2010. 3:34 AM REPLYThe sign of a diode(LED) consists of a triangle and a line. So is the line the negative terminal of the LED and the base of the triangle its positive terminal? Bythe bar I meant the line.

vinet says: Mar 14, 2010. 1:04 AM REPLYHey AI is the bar like thing on the diode sign(LED) signify the negative terminal of the LED?

Artificial Intelligence says: Mar 14, 2010. 1:51 AM REPLY Bar like thing?

vinet says: Mar 12, 2010. 9:00 AM REPLYHi AI don't you require any heat sink for the LED?

Artificial Intelligence says: Mar 12, 2010. 9:22 AM REPLY Hi,Yeah, You should always use a heat sink for both your LED and regulator. And yes, it will work with varying voltage as long as the voltage doesn'texceed the maximum input voltage of the regulator (35V for the LM317).

vinet says: Mar 12, 2010. 9:03 AM REPLYAlso can I use this circuit if I have an input voltage that keeps on changing between 12v to 14v. I will be using a 1watt LED.

http://www.instructables.com/id/Super-simple-high-power-LED-driver/

bbas8 says: Feb 18, 2010. 4:55 AM REPLYJust would like to say thankyou for all your time and replies to everyone. I am learning a lot by how well you explain the different set-ups required byreading thriugh all the comments and links. Hope to build my own soon when i understand enough..:-)

Thanks again.

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