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Power LED s simplest light with constant current
http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ Home Sign Up! Explore Community Submit Power LED's - simplest light with constant-current circuit by dan on January 7, 2007 Table of Contents intro: Power LED's - simplest light with constant-current circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 step 1: What you need . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 step 2: Specs & Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 step 3: wire the LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 step 4: Start building the circuit! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 step 5: keep building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 step 6: add a resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 step 7: add the other resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 step 8: permanant-ize it . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 step 9: finish the circuit! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Advertisements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Customized Instructable T-shirts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ intro: Power LED's - simplest light with constant-current circuit Here's a really simple and inexpensive ($1) LED driver circuit. The circuit is a "constant current source", which means that it keeps the LED brightness constant no matter what power supply you use or surrounding environmental conditions you subject the LED's to. Or to put in another way: "this is better than using a resistor". It's more consistent, more efficient, and more flexible. It's ideal for High-power LED's especially, and can be used for any number and configuration of normal or high-power LED's with any type of power supply. As a simple project, i've built the driver circuit and connected it to a high-power LED and a power-brick, making a plug-in light. Power LED's are now around $3, so this is a very inexpensive project with many uses, and you can easily change it to use more LED's, batteries, etc. i've got several other power-LED instructables too, check those out for other notes & ideas step 1: What you need Circuit parts (refer to the schematic diagram) R1: approximately 100k-ohm resistor (such as: Yageo CFR-25JB series) R3: current set resistor - see below Q1: small NPN transistor (such as: Fairchild 2N5088BU) Q2: large N-channel FET (such as: Fairchild FQP50N06L) LED: power LED (such as: Luxeon 1-watt white star LXHL-MWEC) Other parts: power source: I used an old "wall wart" transformer, or you could use batteries. to power a single LED anything between 4 and 6 volts with enough current will be fine. that's why this circuit is convenient! you can use a wide variety of power sources and it will always light up exactly the same. heat sinks: here i'm building a simple light with no heatsink at all. that limits us to about 200mA LED current. for more current you need to put the LED and Q2 on a heatsink (see my notes in other power-led instructables i've done). prototyping-boards: i didn't use a proto-board initially, but i built a second one after on a proto-board, there's some photos of that at the end if you want to use a proto- board. selecting R3: The circuit is a constant-current source, the value of R3 sets the current. Calculations: - LED current is set by R3, it is approximately equal to: 0.5 / R3 - R3 power: the power dissipated by the resistor is approximately: 0.25 / R3 I set the LED current to 225mA by using R3 of 2.2 ohms. R3 power is 0.1 watt, so a standard 1/4 watt resistor is fine. where to get the parts: all the parts except the LED's are available from http://www.digikey.com, you can search for the part numbers given. the LED's are from Future electronics, their pricing ($3 per LED) is far better than anyone else currently. http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ Image Notes 1. not needed 2. R1 3. Q1 4. recycled 6-volt, 400mA transformer 5. Q2 6. Luxeon Star LED 7. R3 step 2: Specs & Function Here i'll explain how the circuit works, and what the maximum limits are, you can skip this if you want. Specifications: input voltage: 2V to 18V output voltage: up to 0.5V less than the input voltage (0.5V dropout) current: 20 amps + with a large heatsink Maximum limits: the only real limit to the current source is Q2, and the power source used. Q2 acts as a variable resistor, stepping down the voltage from the power supply to match the need of the LED's. so Q2 will need a heatsink if there is a high LED current or if the power source voltage is a lot higher than the LED string voltage. with a large heatsink, this circuit can handle a LOT of power. The Q2 transistor specified will work up to about 18V power supply. If you want more, look at my Instructable on LED circuits to see how the circuit needs to change. With no heat sinks at all, Q2 can only dissipate about 1/2 watt before getting really hot - that's enough for a 200mA current with up to 3-volt difference between power supply and LED. Circuit function: - Q2 is used as a variable resistor. Q2 starts out turned on by R1. - Q1 is used as an over-current sensing switch, and R3 is the "sense resistor" or "set resistor" that triggers Q1 when too much current is flowing. - The main current flow is through the LED's, through Q2, and through R3. When too much current flows through R3, Q1 will start to turn on, which starts turning off Q2. Turning off Q2 reduces the current through the LED's and R3. So we've created a "feedback loop", which continuously tracks the current and keeps it exactly at the set point at all times. http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ step 3: wire the LED connect leads to the LED step 4: Start building the circuit! this circuit is so simple, i'm going to build it without a circuit board. i'll just connect the leads of the parts in mid-air! but you can use a small proto-board if you want (see photos at the end for an example). first, identify the pins on Q1 and Q2. laying the parts in front of you with the labels up and the pins down, pin 1 is on the left and pin 3 is on the right. comparing to the schematic: Q2: G = pin 1 D = pin 2 S = pin 3 Q1: E = pin 1 B = pin 2 C = pin 3 so: start by connecting the wire from the LED-negative to pin 2 of Q2 http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ Image Notes 1. Q2: power NFET. 2. pin 3 3. pin 1 4. pin 2 of Q2, connected to LED-minus wire 5. the LED-plus wire step 5: keep building now we'll start connecting Q1. first, glue Q1 upside-down to the front of Q2 so that it is easier to work with. this has the added benefit that if Q2 gets very hot, it will cause Q1 to reduce the current limit - a safety feature! - connect pin 3 of Q1 to pin 1 of Q2. - connect pin 2 of Q1 to pin 3 of Q2. Image Notes 1. pin 3 of Q1 to pin 1 of Q2 2. pin 1 of Q1 Image Notes 1. connect pin 2 of Q1 to pin 3 of Q2 http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ step 6: add a resistor - solder resistor one leg of resistor R1 to that dangling LED-plus wire - solder the other leg of R1 to pin 1 of Q2. - attach the positive wire from the battery or power source to the LED-plus wire. it probably would have been easier to do that first actually. Image Notes 1. LED-plus wire 2. R1: 100k-ohm Image Notes 1. connect the positive wire from power source step 7: add the other resistor - glue R3 to the side of Q2 so it stays in place. - connect one lead of R3 to pin 3 of Q2 - connect the other lead of R3 to pin 1 of Q1 http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ Image Notes 1. connect R3 lead to pin 3 of Q2. wrap lead around for easy soldering 2. R3, 2.2-ohm glued to side of Q2 Image Notes 1. other lead of R3 to pin 1 of Q1 step 8: permanant-ize it now test the circuit by applying power. assuming it works, we just need to make it durable. an easy way is to put a large blob of silicone glue all over the circuit. this will make it mechanically strong and waterproof. just glob on the silicone, and make an effort to get rid of any air bubbles. i call this method: "BLOB-TRONICS". it doen't look like much, but it works really well and is cheap and easy. also, tying the two wires together helps reduce strain on the wires also. i've also added a photo of the same circuit, but on a proto-board (this one is "Capital US-1008", available at digikey), and with a 0.47-ohm R3. Image Notes 1. BLOB-TRONICS! 2. strain-reduction on the wires http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ step 9: finish the circuit! now connect the negative wire from the power source to pin 1 of Q1. you're done! we'll make it less flimsy in the next step. Image Notes 1. negative from power source to pin 1 of Q1 http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ Related Instructables RGB Color Controllable High Power LED Room + Spot Lighting by dan Super simple high power LED driver by Artificial Intelligence Blinking Nightlight (by request) by inventorjack Dynamo powered LED bike lights by kptBurek Dancing lights by neelandan PC Power 12 V Current Limiter by neelandan LED Lightbulb by Tool Using Animal A remote controlled power RGB LED mood light. by 5Volt Advertisements Customized Instructable T-shirts http://www.instructables.com/id/Power-LED_s simplest-light-with-constant-current/ Comments 50 comments Add Comment view all 116 comments Artificial Intelligence says: Mar 19, 2008. 9:59 AM REPLY Very cool, but not the simplest. Watch this http://www.instructables.com/id/Super-simple-high-power-LED-driver/ dan says: Mar 19, 2008. 11:03 AM REPLY thanks, i covered your circuit here: http://www.instructables.com/id/EVKHFD64UZEWP86K7M/ the problem with it is that using an LM317 it has a high dropout (3.5v) so your efficiency is poor unless you are using many leds in series. you can do a little better with a different regulator model. ewitte says: Aug 30, 2008. 5:23 PM REPLY Would this be good to run with 6 at 12v with a .33ohm resistor? That gives 1.515A with it dropping to .7575 running series two sets of 3. Some are 3W and some are 5W but I decided to run them all between .7 and .8ma because I have 50+ to power in all ;) ewitte says: Oct 2, 2008. 3:45 AM REPLY I've got 16 on this now working my way up to the full 56. A tip I have for keeping the efficiency up. Usually what I do is use 3.6v for blue and 2.4- 2.5 for red and calculate without the 0.5v of the circuit. When I'm finished its usually barely warm if even that. I'll throw an extra 1v on to see if it brings the light up, if it does I stay if not go back. Usually I'm working at 15-18v. Artificial Intelligence says: Mar 19, 2008. 12:06 PM REPLY But I'm from Denmark and the LD1585CV or LM1084IT-ADJ is not available here. Gopher says: Jul 26, 2008. 3:11 PM REPLY OK, I need a circuit to power a 3W luxeon LED that is powered by 4AA batteries, which is easy enough in itself, however I would like to be able to have the LED at quite a high frequency (5 - 10pulses per second) and preferably with a constant current (thought the last bit isnt essential) I cant give specifics of the Luxeons as I intend to use it on a range of models/makes etc so something to cover most bases will be great does anyone have a diagram of such a circuit or an idea where to finf one etc samphantom says: Jun 23, 2008. 5:43 AM REPLY Hello every one. Hello Dan, I like your circuit. I have a Led @1W from digikey part # 475-2587-1-ND. I implemented a driver with an LM317 an couple resistors, the LM317 has heat sink, the problem is the LED needs 1.4A to give the tolerance brightness with no problem @3.5V. This LED needs also a heat sink to avoid overburn, I put a 0.27R resistor @1/2W with no problem but the leds still need a little fan to avoid over heating. Could you help me to make a circuit for this specific LED avoiding heatsinks? I armed the circuit because I saw it on internet but yours seems so simple. Thank you beforehand. 1up says: Apr 13, 2008. 1:21 PM REPLY This looks nice! I might use this sometime. Could this circuit also be used as a driver for a laser diode? raygromer says: Apr 1, 2008. 4:29 PM REPLY Great one Dan. I've used it successfully on a couple projects already. But it won't work on the project I'm working on now because my LED cathode legs must connect directly to ground (battery negative). Is it possible to change the polarity of your circuit so the LED anode side is "regulated" and the LED cathodes connect directly to ground? Thanks! krunal_299 says: Apr 1, 2008. 3:03 AM REPLY Hi! My requirement is for 350ma LED and Vf=3.5v. So does it require Heat sink in this ckt.? Thanks & regards! [...]... voltage? or is it one brightness solves all? http://www.instructables.com/id /Power- LED_ s -simplest- light- with- constant- current/ mori says: Oct 21, 2007 6:02 PM REPLY ooo Already answered i think by a different thread http://www.instructables.com/id/Blue -LED- light- box/ dan says: Oct 24, 2007 11:05 PM REPLY see my 'power led circuits' instructable, it has a couple methods of converting this circuit for... brightness and 100% brightness but that 's another issue maybe Maybe something that shunts the FET gate to ground when positive bias is applied? BlessedWrath says: Sep 3, 2007 9:14 AM REPLY Can this circuit be used as a driver circuit for laser diodes? I assume so, but wanted to be sure Is there any reference material I can download to begin to understand why these components are necessary, and what is happening... dan says: Aug 16, 2007 4:24 PM REPLY no, you are not misunderstanding that 's why you are not seeing LED lightbulbs at home depot yet johnpombrio says: Mar 30, 2008 7:13 PM REPLY Closer than you think, now (1 1/2 years later)! Home Depot has LED stickies (3 LEDS using 3 AAA batteries), 7 LED light Pucks on a transformer (similar to the Halogen pucks) IKEA DOES have LED small reading lamps which I use... voltage at base of Q1 goes up, turning it on this is a feedback system 2) yes, if a led shorts out then the voltage drop will be across Q2 Jamshed says: Oct 17, 2007 10:03 AM REPLY Hello Dan, I mean to ask, if an led gets open then there will be no voltage drop across the NFET Q2 So, this means Q2 is off Now with Q2 off(because of open led) , how the base of Q1 is going to be triggered? trons says: Oct 16,... REPLY Just to make sure I understand, you are saying no resistor is ok with the conditions you mention? Would it add any safety factor to put like a 1ohm resistor in series with each led? Thanks!!! dan says: Dec 7, 2007 1:45 PM REPLY correct if you follow the above notes, i would not bother with resistors unless this is a commercial product you are making yes - adding a resistor will improve the safety... happening with the physics of the electricity? http://www.instructables.com/id /Power- LED_ s -simplest- light- with- constant- current/ technomorph says: Aug 23, 2007 3:59 PM REPLY Hey Dan, Love it, How would you add more LEDs to the circuit In series? In Parrallel? Is there anything else that needs to be modified? thanks evox says: Jul 10, 2007 2:41 AM REPLY Hi Dan i realize this is a stupid question and... decreasing the luminosity of the light I'm not quite sure if it does this by varing the current or the voltage of the devices, but from what you're saying this device is either ON or OFF? re: "it keeps the LED brightness constant no matter what power supply you use or surrounding environmental conditions you subject the LED' s to" So is there anyway of modifying the luminosity of the LED via the supply... Richard http://www.instructables.com/id /Power- LED_ s -simplest- light- with- constant- current/ callmeshane says: Jan 31, 2008 12:23 AM REPLY Uhhhh N-Fet 's, F-Net 's, Fet-Net 's and Nut-Fat 's - does anyone ever use F-it 's? I am trying to be funny, and overcome my default setting at retarded, mentally defective and lazy Actually this device is pretty much what I want to make up, to run a similar system Only I like... Luxeon I 's in parallel to this circuit? Or can you only safely go parallel with strings of minimum 2 series LEDs? I was thinking of using an mATX PSU 's 5V line to drive the Luxeons in pairs, each sharing a driver with 700 mA output (I have 12 LEDs, 8 are from the same batch 0473468, the other 4 are batch 0473467) Thanks in advance Tomteslakt says: Sep 7, 2007 3:30 AM REPLY Cool! If this circuit is used... of your LED Instructables I built my first one already and it was a-ok I was checking out some other LED Instructables and found this which uses a large capacitor before the LEDs to get a fade-out effect Would this be possible with your circuit and if so any recommendations for the caps? I would love to have that nice blue light do a soothing fade as it drifts off into sleep altaria1993 says: all the . http://www.instructables.com/id /Power-LED_ s simplest-light-with-constant-current/ Home Sign Up! Explore Community Submit Power LED's. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 http://www.instructables.com/id /Power-LED_ s simplest-light-with-constant-current/ intro: Power LED's - simplest light with. and you can easily change it to use more LED's, batteries, etc. i've got several other power-LED instructables too, check those out for other notes & ideas step 1: What you need Circuit