High-power LED's: the future of lighting!

but... how do you use them? where do you get them?

1-watt and 3-watt Power LED's are now widely available in the $3 to $5 range, so i've been working on a bunch of projects lately that use them. in the process it was bugging me that the only options anyone talks about for driving the LED's are: (1) a resistor, or (2) a really expensive electronic gizmo. now that the LED's cost $3, it feels wrong to be paying $20 for the device to drive them!

So I went back to my "Analog Circuits 101" book, and figured out a couple of simple circuits for driving power LED's that only cost $1 or $2.

This instructable will give you a blow-by-blow of all the different types of circuits for powering Big LED's, everything from resistors to switching supplies, with some tips on all of them, and of course will give much detail on my new simple Power LED driver circuits and when/how to use them (and i've got 3 other instructables so far that use these circuits). Some of this information ends up being pretty useful for small LED's too

here's my other power-LED instructables, check those out for other notes & ideas

This article is brought to you by MonkeyLectric and the Monkey Light bike light.

Step 1: Overview / Parts

There are several common methods out there for powering LED's. Why all the fuss? It boils down to this:
1) LED's are very sensitive to the voltage used to power them (ie, the current changes a lot with a small change in voltage)
2) The required voltage changes a bit when the LED is put in hot or cold air, and also depending on the color of the LED, and manufacturing details.

so there's several common ways that LED's are usually powered, and i'll go over each one in the following steps.


This project shows several circuits for driving power LED's. for each of the circuits i've noted at the relevant step the parts that are needed including part numbers that you can find at www.digikey.com . in order to avoid much duplicated content this project only discusses specific circuits and their pros and cons. to learn more about assembly techniques and to find out LED part numbers and where you can get them (and other topics), please refer to one of my other power LED projects.

Hi. <br><br>Dan or anyone who can help a novice design a circuit to use the AC mains in my house (110V) to drive an LED panel I am making using 3W high power full spectrum LEDs. So source current is 110v AC but I need to convert to DC and I want to run individual strips (5 strips of 5 x 3W LEDs for a total of 25 3W LED) of 5 each of the LEDs. The LEDs have a forward voltage between 3.0-3.2V at 700 mA. I'd like to run at constant current and fixed voltage of about 3.1V. <br><br>Any help would be great. Thanks.
dear sir I have a super bright led. 10 watt, 12 volts and 1 ampere. pls help me how can it be flashing from bike.
<p>Hi,</p><p>Wow, great article!</p><p>Can someone please tell me if the circuit in step 10 - the analog adjustable driver - is a constant current driver, and is stable across ambient temperature changes?</p><p>Many thanks,</p><p>Jonners.</p>
Hi. <br>I have a 96W COB chip that has unusually high voltage requirements. It needs 70-90VDC to light at 1.5A. I want to build a driver for it. Can you recommend parts I would need to use 110VAC as my supply. <br>Thanks. <br>Matt
<p>another thought </p><p>could I just use an extra 3W 1A bead to forward another 3 volts to the 10w chip </p><p>I believe the 10w LED draws 10.5V and if I used another 3.4V LED that would put me at 13.9 V my 100 AMP PSU can be overvolted to 13.65V </p><p>would this keep the LED's in a range where they will not try and draw more current? </p><p>also if I used 2x 500ma PTC parallel would that then handle 1amp with 2 amp cut off ? </p><p>I was thinking instead of using diodes to drop voltage why not just use an LED and an 3w LED bead should have the same current rating as the 10w </p>
<p>I bought 10w LED <br> I believe they have 3x1w beads in series and 3x parallel runs ( 9 beads )<br><br>when combining LED's in series does their running current also increase ? <br><br>ie) if they where 1w 3.5v 350ma beads would they cut out at 1050ma ?<br> or would they still cut-out at 350 current and use 1050ma power ? <br><br>I had ordered 500ma PTC but now thinking I really needed something a lot lower </p>
I have 12v, 10w bright led, can u help me to build drive circuit from 220v
<p>I can confirm that this circuit works, but a couple things to mention. You definitely want to do your math right or your MOSFET will get pretty hot. It wont take much to get this baby hot. Second, if you have a stable power source from your power supply, there really isn't a need to control your current in such a manner. Simply using a resistor in series with your LEDs will work. The MOSFET can and should be used to soft start your LEDS extending there overall lifespan. Also when using a MOSFET, adding some TVS diodes to protect it is a good idea specifically gate to source.</p>
<p>I really don't think the pptc is regulating the current. It is just protecting the battery from excessive current draw and posibly explosion.</p><p>As the pptc needs time to warm up under overcurrent conditions, the led will probably die before it trips. And if it does not trip, the resistance over the pptc is fairly low. Transition from not-tripped to tripped is fairly fast.</p><p>This sounds more like the 'throwie' principle where the battery's internal resistance will limit the current, combined with the small margin the driving voltage is over the needed forward voltage of the led.</p><p>I wish I had the necessary components to test this out. My 250mA pptc did not play nice with my 20mA leds :(</p>
<p>PLEASE PLEASE HELP!</p><p>I have a Constant Current LED driver module that I removed <br>from a LED grow light, rated 80-100V @ 600ma. It currently runs a 45 LED <br>string. It says that it&rsquo;s a HP060 but it doesn&rsquo;t look like anything I&rsquo;ve seen <br>that matches that on the web. I can&rsquo;t really see any of the part numbers, but <br>there&rsquo;s a transformer surrounded by smaller components, including the only <br>adjustable thing, a little blue potentiometer. (I have no schematic, but I <br>assume this might be a &ldquo;typical&rsquo; circuit.)</p><p>What I want it to do is to run a 23 string @ the same <br>rating. The PROBLEM is that when I do, the supply kicks the total voltage down <br>to equal the same voltage across each LED. Basically, I am trying to double the <br>voltage at the same current, but it won't let me. (The LEDs are rated at over <br>double their current power so I am not worried about blowing them.)</p><p>Real world:</p><p>I measure across the LED while 45 of them are on and the <br>voltage is 2.225VDC @ 600ma. I then short the string to 23 and measure and it <br>is still 2.225VDC@600ma, but I want 4.45VDC@600ma across each LED. (<a href="mailto:2.225@1200ma" rel="nofollow">2.225@1200ma</a> would do but I don&rsquo;t think this <br>thing will do it.)</p><p>Like I said, there's a micro blue potentiometer on this <br>module and I don't know what it does (nor do I have a schematic) but I need to <br>know what to do to adjust this up to 4.45VDC.<br> <br><br> <br>I&rsquo;m assuming there&rsquo;s some kind of resistance sensing circuit going on, but I&rsquo;m <br>looking at it and I see the transformer, a couple of what look to be SCRs on <br>heatsinks, a choke, three electrolytic caps (and some smaller caps, too), and <br>the potentiometer. I&rsquo;m not comfortable randomly adjusting the pot when I don&rsquo;t <br>know what it does.<br> <br><br> <br>(As well, a miniature supply that could do what I want would be considered, <br>too.)</p><p>I need this, like, 8 years ago so please help!</p><p>Will</p>
<p>Hello!</p><p>I wish you a nice day!</p><p></p><p>We are looking for LED drivers and dimmers for project. We <br>have finished with wiring.</p><p>Lighting system in that project have about 450 meters of LED <br>strips inside aluminum profiles recessed in ceiling, separated in parts <br>with lenghts 0.75 m, 1 meter, 1.5 meter and 2 meters.. Also, there are parts <br>with individual lenghts of 5.4 m, 3.2 m.... Type of LED strip is 3014 SMD <br>14,4 W/m, input voltage DC 12V, 120pcs/m, pure white color. So, that is <br>450(m)x14,4(W/m)=6480W, around 6,5kW power of whole system at full load. Lighting system <br>must be dimmable and wireless controlled. I need help with choosing right LED drivers and controllers for system. You can see project in attachment.</p><p>Thank you in advance.</p>
<p>Trying to wrap my head around this and I've got a few questions that hopefully somebody can clear up.</p><p>1. &quot; LED current is approximately equal to: 0.5 / R3.&quot; </p><p>Is he using the value of 0.5v because that is the &quot;Vce Saturation (Max)&quot; value for Q1, the 2N5088BU transistor? If not, where does it come from?</p><p>2. &quot;The input voltage can be as little as 0.6 volts higher than the output voltage.&quot; </p><p>Is this also determined by the &quot;Vce Saturation (Max)&quot; value for Q1? If not, then where does it come from? </p><p>3. &quot;The power dissipated by R3 is approximately: 0.25 / R3.&quot; </p><p>Where does the 0.25 come from? Is it calculated as 1/2 of whatever the 0.5 volts is from my first two questions?</p><p>4. &quot;Q2 can only handle 2/3 watt before you need some kind of heatsink. with a large heatsink, this circuit can handle a LOT of power &amp; current - probably 50 watts and 20 amps with this exact transistor.&quot; </p><p>Is he talking about the MOSFET burning up 50 watts on it's own, or 50 watts for the entire circuit, LEDs included?</p><p>5. Considering that the &quot;dropout&quot; remains constant at higher voltages, and assuming that the input voltage stays tuned to this level; would it be true to say that this circuit becomes more efficient with higher power LEDs? </p>
<p>I've been studying and designing some modules based off of your schematics.<br><br>I am interested in an *even simpler* setup to power two sets of 3W LEDs. They will both share a 24V power supply. The first set uses six 3W LEDs (3.2-3.8V). This should be straight forward. My concern pertains to the second set. The second set only has two 3W LEDs (3.2-3.8V). Will the circuit drop the voltage to what the LEDs only need?</p>
<p>I received my parts and can confirm that the &quot;even simpler&quot; takes care of the voltage difference too. :)</p>
<p>hello, </p><p>for step 10, how can i calculate the voltages and currents? I want to modify this curcuit for different types of power leds. </p><p>thank you and have a nice day! :) </p>
<p>This is the first pcb I designed that uses this instructable to power 16 1w LEDs. I later made a 48 output design. The most I have daisy chained is 109 for a light wall in a reastruant.</p>
<p>Hello,</p><p>I've had great success with Schematic #4. I'm dimming 4 - 3 watt LED's. I'm powering them with a 20 volt supply. My question is, since this is a constant current device, can I power a single 3 watt led (forward voltage of 4 volts) with the same 20 volt supply? Is this a good idea?</p><p>Thank You</p>
<p>Hi there, this is a very good instructable with nice presentation.</p><p>I am planning to build constant current source #1.</p><p>Led : 10 W</p><p>Forward Voltage : 9-11 V.</p><p>Forward Current : 1050 mA.</p><p>Input Voltage : 12 V 5 A.</p><p>I assume R3 is 0.476 ~ 0.5 Own. Is it right?</p><p>I can't find the parts you suggested in local electronic stores. I could find only 2N2222, BC547 (Q1) and IRF640N (Q2).</p><p>If I use those transistors instead of the ones in the guide, what changes do I have to make?</p>
<p>your circuit is good cost effective need thermal compassion . </p>
<p>Thanks for your Instructable! Using your even simpler current source and a <br>10W RGB LED my pumpkin really glows!!!!!! I used the cheaper <br>LM1084IT-ADJ regulators and some IRLB8721PbF N-Channel Mosfets to <br>turn the circuit on and off using an Arduino UNO. The video can be <br>seen on YouTube <a href="http://youtu.be/ry2G-STAhl8" rel="nofollow">http://youtu.be/ry2G-STAhl8</a></p><p>The <br>library for the Arduino UNO was another instructable here: <br><a href="http://www.instructables.com/id/RGB-lamp-with-Custom-Moodlamp-Library/" rel="nofollow">http://www.instructables.com/id/RGB-lamp-with-Custom-Moodlamp-Library/</a></p><p>Thanks <br>to great contributors like you, this week I made a pumpkin that can <br>be seen from blocks away and I found out that the Hedgehog averages <br>about 6 miles a night on his wheel! I'm off to start my next <br>Instructables project!</p>
<p>Hello,</p><p> This is a great tutorial, I have all of the parts and built the #4 circuit. Now I want to use it to power 4X - 4.1 Volt 700 mA LED's. I tried to test the current output using 18 regular green LED's and the circuit will only pull ~ 40 mA's according to my DMM at full on no PWM signal. I am powering with a 40 volt 2 amp powersupply. I have the components listed and am using a 0.18 ohm resistor (R3) with theoretical current available up to 2.5 amps. R1 = 100k and the zener is 5.1 volts. What am I missing? </p><p>Question: What can I use for a dummy load to test my circuit? I have seen tutorials that use regular diodes (1N4005's) in series and then a series resistor to give the proper current draw? I've got a bunch of 1N4007's around, so i'm tempted to make several strings and test with that?</p><p>Thank You!</p>
<p>Hi Dilshan, I am building a battery powered LED torch with 4X1.2V 1200mA batteries, and 3X3W LEDs I am trying hard to find a driver which could do the job of connecting them together</p><p>the LEDs I have are,<br>LED, HIGH POWER, 5000K, 70CRI, 275LM<br>Series: LUXEON TX<br>LED Colour: White<br>Luminous Flux @ Test: 369lm<br>Forward Current @ Test: 1A<br>Forward Current If Max: 1.2A<br>Forward Voltage @ Test: 2.86V.<br><br>could you please help me what should be the specifications of the driver??</p>
<p>.your voltage is very near so no need of regulators why not a resistor actually this regulator is needed if supply is fluctuating its output.</p><p>according to your calc.=0.64ohm resistance will work</p><p>so use 2=1ohm and 2 ohm 5w resistances in parallel to get .66 ohm</p><p>1.94/0.66=2.93A for 3 led and 0.97A for 1 led</p><p>remember NI-MH cells have voltage somewhat1.35-1.15 volts in my different calculations but doesn't makes difference too much i.e. doesn't kills led. Especially if led are connected to heat sink</p>
<p>I would avoid cranking them to their maximum current (If Max of 1.2A) because that will shorten their life span (and also increase heat output).</p><p>4x 1.2V = 4.8V (when fully charged, of course). Batteries are very likely 1200mAh (the little h is important: milli Amp HOURS)</p><p>3 of your LEDs in series = 3x2.86V = 8.58V, so nearly 2x your max battery voltage: you'd need a boost circuit to achieve that (i.e you won't get far with this circuit driving them because your input voltage isn't high enough). In series, you'd pull the 1A (at test), which is near the total Ah capacity of your batteries (but this would first require your batteries to provide 8.58V+, which they do not). Assuming you added 3 more 1.2V batteries (7x1.2 = 8.4V), you wouldn't have especially bright LEDs, and your battery voltage would still plummet like a rock, and eventually not actually drive the LEDs.</p><p>If you instead ran the LEDs in parallel (requiring lower voltage but higher current), you could drive them at a little more than 1/2 of your battery voltage (a switching regulator would be a decent approach). In such a configuration however, you would need to provide _3_AMPS_, which would cause your batteries to heat up, and their voltage would drop even faster.</p><p>In general, lower current, higher voltage (LEDs in series, not parallel) is preferable. Ohms Law will kick your butt: high current causes small resistances (including what occurs within the batteries as they heat under load) to result in larger voltage drops. This is the basic premise behind high voltage power transmission lines.</p><p>LEDs like this are intended to run off of something more than a few rechargeable AA batteries. An 18650 Li-Ion gives you 3.7V rated at say 2.4Ah (2400mAh, but that's at 3.7V not 1.2V). One such battery would be circa 1 hour of runtime for your lighting setup, and as the power supply for Dan's circuit, would not require a significant voltage drop (and thus dissipation).</p><p>I've had decent results from using a switching &quot;buck&quot; converter driving a 3W LED using a partially depleted 9V battery. At 8V or so, the 9V has outlived it's useful life as a 9V in whatever plug-in application it had, but clear on down to as low as 5V or so, it's still a good power source for a buck converter - you can drive a 3W LED quite nicely. Not for hours, but the battery was essentially trash to start with.</p>
<p>Hi,</p><p>Could l know how do you come up with the equation I = 0.5/R3 please?</p>
<p>An easier to understand and use explanation might be, given a known LED current rating of say 20mA (0.020 A), to determine the necessary resistance of R3:</p><p>R3_in_ohms = 0.5 / (desired_current_expressed_in_amps)</p><p>0.5 / 0.020 = 25 (ohms)</p><p>Does that help?</p>
<p>I have also a problem with this equation, were do you get the 0.5 from?</p>
<p>Hi!</p><p>(I apologize for my crappy english)...</p><p>This is the way I see it. As you can see on the diagram, the NPN transistor emitter is wired to ground and the base is wired to the power resistor. When the transistor is well... &quot;polarized&quot; (don't know how else to say it), a fixed voltage should appear between the base and the emitter. In the case of a 2N3904, the base to emitter voltage is approximately 0.58V, which is the same voltage drop on the power resistor... So, if you use this transistor, the current flowing would be I = 0.58/R3 (this is Ohm law V = I*R).</p><p>I hope you can understand my english...</p>
<p>&quot;biased&quot; is likely the term you're looking for.</p><p>The FET is effectively a voltage controlled variable resistor. It (and well, the diode series) forms one half of the voltage divider circuit (coming from Vcc reference), which R3 is the other half of (going to ground reference). The lower the R3 resistance, the &quot;closer to ground&quot; the base of Q2 will be, and therefore the higher current (in the form of a lower FET D-S resistance) can flow through Q1. Raise R3, and the base of Q2 will be more positive, thus conducting the Q1 gate to ground, causing the Q1 D-S to have a higher resistance, and reducing the flow through the diodes.</p><p>The 0.5 figure seems like a reasonable ballpark figure for the voltage at which the Q2 base would be within the &quot;region of operation&quot;, while not being saturated. The value would vary with the transistor being used - chiefly with the part type (refer to the data sheet), but also individual characteristics.. If one had a good transistor tester, you could get the Vbe(sat) of an individual candidate transistor and tune the resistor value to that.</p><p>Note that use of a Q2 with a higher Vbe(sat) voltage would allow for use of a nominally higher resistance value for R3, which may be easier to acquire. You don't want to use too low a resistance value, or the BJT will burn itself up.</p><p>Vbe(sat) for the PN2222A transistor is 0.6-1.2V for 15mA base current and 150mA of collector current. This represents _saturation_ (full-on), which is not where the transistor will (or should) be operating while it is regulating the current</p><p>Remember, the total resistance between the resistors and the ground is R3 + whatever the FET has been regulated to. The FET is the primary current regulator here.</p><p>FTR, your English is entirely understandable, and better than many who presumably communicate in it as a first language...</p>
Link to PWM 555 thingy is dead (end of step 8).
<p>Here is an archived copy </p><p><a href="https://web.archive.org/web/20040206235116/http://www.cpemma.co.uk/555pwm.html" rel="nofollow">https://web.archive.org/web/20040206235116/http://www.cpemma.co.uk/555pwm.html</a></p>
<p>Thanks for the shematic! The LM317 driver is too wasteful for one LED but this is just perfect. I used a 2N2222 NPN Transistor which has a Base Emitter Saturation Voltage of 0.6V. I didn't have any 1 Ohm resistors so I had to take about ten 10 Ohm ones ;)</p>
<p>I have built a bunch of these little circuits, and they work really well. Thank you for posting this! Here I built four driving a color LED with an micro controller and a pot. I encased it with liquid plastic for protection. You can adjust the LED cycle speed with the pot. I use a single lipo to power everything. Fun!</p>
<p>I need to drive 5 3W RGB LEDs in series using an arduino. The maximum current required is 350mA each for R G and B dyes.<br>and minimum current requirement is 2.4V, 2.4V and 3.5V respectively.<br></p><p>What should I use to interface the LEDs with my arduino as the output current of each arduino pin is 50mA maximum</p>
<p>You need MOSFETs my friend (though a darlington may well suffice), i would recommend you read up on the topic of signal amplification and driving power using transistors :)</p>
<p>Hi Pratham, were you able to solve your query since I am also looking for the response to a similar query</p>
<p>Hi, I was into final exam on making LED lamp.</p><p>May i know which circuit the best for driving 48 LEDs simultaneously?</p><p>the LED forward voltage will be 2.8-3.2v and max forward current is 20mA.</p><p>thanks.</p>
<p>How to Connect 10*1w led to this circuit. what changes I have to make in circuit </p>
<p>Would a TIP41C be a good substitute for Q1 (the 2N5088)? I'd like to make sure I have enough headroom heat-wise, as I plan on putting the circuit in an enclosed area with no ventilation. Are there any other possible modifications I might have to make to the circuit (adjusting the value of R3, etc) to accomodate this? Thanks!</p>
<p>Upon looking at the TIP41C's datasheet more closely, it seems the forward gain is significantly smaller than the 2N5088. Would perhaps a TIP122 be a better replacement instead?</p>
<p>Muy bueno!!!! Ya lleva poco m&aacute;s de dos a&ntilde;os funcionando!!!</p>
<p>Ref to <a href="http://www.instructables.com/id/Yet-Another-Daft-Punk-Coffee-TableDisplay/" rel="nofollow">http://www.instructables.com/id/Yet-Another-Daft-P...</a> any idea how I can get y query solved. </p><p>I want the same matrix display on the higher powered LEDs ( 3 W would be good enough). </p><p>Thanks in advance</p>
<p>Thank you for these schematics. I used them on my sequential taillights for my car : <a href="http://www.dodgeintrepid.net/showpost.php?p=2697473." rel="nofollow">http://www.dodgeintrepid.net/showpost.php?p=269747...</a> </p><p>I shared the link to your article in this forum, I hope you don't mind. There's also a video of the final result. </p><p>The picture included is just a &quot;fly bug&quot; design ^^ IRF640 and BC547B, I used it for testing ;)</p>
<p>Awesome tutorial on LEDs and drivers thereof, thank you!</p>
<p>thank you fr this excellent tutorial, I need help for a project, I need to use the high power LEDs listed bellow, 2 of them in series, can you help me to drive them please?</p><p>http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Arrays-NonDirectional/XLamp-CXA3590</p>
<p>Hi all... Can anybody tell me if it would be possible to adapt circuit #5 to allow for either direct voltage in or PWM. In other words, can I add to the circuit and have it so that it work via PWM but if there is no PWM signal it will still work without it. Something like this...</p>
Hi dan good work buddy just wanted to as how many leds can you run on circuit 3# the one you say is the best<br>Regards phil
<p>Hi </p><p>I want to power my bike headlight for 1watt X 2 leds and my alternator may be powering some where to 14.5v -16.5 v at 4-5 amps</p><p>battery capacity at 12v 7 amps </p><p>Will your basic circuit work without failure </p>
I've made this diagram with an IRL540 as Q2 and for Q1 I used a BC549. <br>The calculation for R3 was slightly off. In the example is given 0.5/Milliamps=R3. I've tried this for 700mA 0.5/0.7=7,142857142857143 (0.75 Ohm resistor). But my current was way to high with this resistor. Then I slightly increased the resistor to 1 Ohm. at this moment the current is 640 mA. I believe this is due to the fact the collector saturation voltage of the BC549 is somewhat higher 600mV. <br> <br>All seems to be working now. There's only one thing I wonder. What about the power consumption. Is there a large difference between the fancy LED drivers you can buy in the shop for a lot of money?
I want to create a 8 led light bar( each led requires 3.2 volts and 350ma ) Is this the circuit i need because the #'s aren't adding up. if I don't use one of these circuits i am just going to use resistors alone I just wanted something to condition the power more because I will be using a 7.2 volt 1600 mah battery and as it drains I don't want the leds to dim

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Bio: Dan Goldwater is a co-founder of Instructables. Currently he operates MonkeyLectric where he develops revolutionary bike lighting products. He also writes a DIY column for ... More »
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