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High Power LED Driver Circuitsby dan on January 8, 2007

Table of Contents

High Power LED Driver Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro:   High Power LED Driver Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1:   Overview / Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 2:   Power LED performance data - handy reference chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 3:   Direct Power! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 4:   The humble resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 5:   $witching regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 6:   The new stuff!! Constant Current Source #1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 7:   Constant current source tweaks: #2 and #3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 8:   A little micro makes all the difference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Step 9:   Another dimming method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Step 10:   The analog adjustable driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Step 11:   An *even simpler* current source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Step 12:   Haha! there's an even easier way! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Author:dan    MonkeyLectricDan Goldwater is a co-founder of Instructables. Currently he operates MonkeyLectric where he develops revolutionary bike lighting products. He also writes aDIY column for Momentum magazine.

Intro:  High Power LED Driver CircuitsHigh-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 wasbugging 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, itfeels 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 onall 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 usethese 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

Step 1: Overview / PartsThere 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.

Parts

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 thatyou 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 aboutassembly 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.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Step 2: Power LED performance data - handy reference chartBelow are some basic parameters of the Luxeon LED's which you will use for many circuits. I use the figures from this table in several projects, so here i'm just puttingthem all in one place that i can reference easily.

Luxeon 1 and 3 with no current (turn-off-point):white/blue/green/cyan: 2.4V drop (= "LED forward voltage")red/orange/amber: 1.8V drop

Luxeon-1 with 300mA current:white/blue/green/cyan: 3.3V drop (= "LED forward voltage")red/orange/amber: 2.7V drop

Luxeon-1 with 800mA current (over spec):all colors: 3.8V drop

Luxeon-3 with 300mA current:white/blue/green/cyan: 3.3V dropred/orange/amber: 2.5V drop

Luxeon-3 with 800mA current:white/blue/green/cyan: 3.8V dropred/orange/amber: 3.0V drop (note: my tests disagree with spec sheet)

Luxeon-3 with 1200mA current:red/orange/amber: 3.3V drop (note: my tests disagree with spec sheet)

Typical values for regular "small" LED's with 20mA are:red/orange/yellow: 2.0 V dropgreen/cyan/blue/purple/white: 3.5V drop

Step 3: Direct Power!Why not just connect your battery straight to the LED? It seems so simple! What's the problem? Can I ever do it?

The problem is reliability, consistency & robustness. As mentioned, the current through an LED is very sensitive to small changes in the voltage across the LED, and alsoto the ambient temperature of the LED, and also to the manufacturing variances of the LED. So when you just connect your LED to a battery you have little idea howmuch current is going through it. "but so what, it lit up, didn't it?". ok sure. depending on the battery, you might have way too much current (led gets very hot and burnsout fast), or too little (led is dim). the other problem is that even if the led is just right when you first connect it, if you take it to a new environment which is hotter or colder,it will either get dim or too bright and burn out, because the led is very temperature sensitive. manufacturing variations can also cause variability.

So maybe you read all that, and you're thinking: "so what!". if so, plow ahead and connect right to the battery. for some applications it can be the way to go.

- Summary: only use this for hacks, don't expect it to be reliable or consistent, and expect to burn out some LED's along the way.

- One famous hack that puts this method to outstandingly good use is the LED Throwie.

Notes:

- if you are using a battery, this method will work best using *small* batteries, because a small battery acts like it has an internal resistor in it. this is one of the reasons theLED Throwie works so well.

- if you actually want to do this with a power-LED rather than a 3-cent LED, choose your battery voltage so that the LED will not be at full power. this is the other reasonthe LED Throwie works so well.

Step 4: The humble resistorThis is by far the most widely used method to power LED's. Just connect a resistor in series with your LED(s).

pros:- this is the simplest method that works reliably- only has one part- costs pennies (actually, less than a penny in quantity)

cons:- not very efficient. you must tradeoff wasted power against consistent & reliable LED brightness. if you waste less power in the resistor, you get less consistent LEDperformance.- must change resistor to change LED brightness- if you change power supply or battery voltage significantly, you need to change the resistor again.

How to do it:

There are a lot of great web pages out there already explaining this method. Typically you want to figure out:- what value of resistor to use- how to connect your led's in series or parallel

There's two good "LED Calculators" I found that will let you just enter the specs on your LED's and power supply, and they will design the complete series/parallel circuitand resistors for you!

http://led.linear1.org/led.wizhttp://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

When using these web calculators, use the Power LED Data Handy Reference Chart for the current and voltage numbers the calculator asks you for.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

if you are using the resistor method with power LED's, you'll quickly want to get a lot of cheap power resistors! here's some cheap ones from digikey: "Yageo SQP500JB"are a 5-watt resistor series.

Step 5: $witching regulatorsSwitching regulators, aka "DC-to-DC", "buck" or "boost" converters, are the fancy way to power an LED. they do it all, but they are pricey. what is it they "do" exactly? theswitching regulator can either step-down ("buck") or step-up ("boost") the power supply input voltage to the exact voltage needed to power the LED's. unlike a resistor itconstantly monitors the LED current and adapts to keep it constant. It does all this with 80-95% power efficiency, no matter how much the step-down or step-up is.

Pros:- consistent LED performance for a wide range of LED's and power supply- high efficiency, usually 80-90% for boost converters and 90-95% for buck converters- can power LED's from both lower or higher voltage supplies (step-up or step-down)- some units can adjust LED brightness- packaged units designed for power-LED's are available & easy to use

Cons:- complex and expensive: typically about $20 for a packaged unit.- making your own requires several parts and electrical engineering skillz.

One off-the-shelf device designed specially for power-led's is the Buckpuck from LED Dynamics. I used one of these in my power-led headlamp project and was quitehappy with it. these devices are available from most of the LED web stores.

Step 6: The new stuff!! Constant Current Source #1lets get to the new stuff!

The first set of circuits are all small variations on a super-simple constant-current source.

Pros:- consistent LED performance with any power supply and LED's- costs about $1- only 4 simple parts to connect- efficiency can be over 90% (with proper LED and power supply selection)- can handle LOTS of power, 20 Amps or more no problem.- low "dropout" - the input voltage can be as little as 0.6 volts higher than the output voltage.- super-wide operation range: between 3V and 60V input

Cons:- must change a resistor to change LED brightness- if poorly configured it may waste as much power as the resistor method- you have to build it yourself (oh wait, that should be a 'pro').- current limit changes a bit with ambient temperature (may also be a 'pro').

So to sum it up: this circuit works just as well as the step-down switching regulator, the only difference is that it doesn't guarantee 90% efficiency. on the plus side, it onlycosts $1.

Simplest version first:

"Low Cost Constant Current Source #1"

This circuit is featured in my simple power-led light project.

How does it work?

- Q2 (a power NFET) is used as a variable resistor. Q2 starts out turned on by R1.

- Q1 (a small NPN) 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 monitors the LED current and keeps it exactly atthe set point at all times. transistors are clever, huh!

- R1 has high resistance, so that when Q1 starts turning on, it easily overpowers R1.

- The result is that Q2 acts like a resistor, and its resistance is always perfectly set to keep the LED current correct. Any excess power is burned in Q2. Thus for maximumefficiency, we want to configure our LED string so that it is close to the power supply voltage. It will work fine if we don't do this, we'll just waste power. this is really theonly downside of this circuit compared to a step-down switching regulator!

setting the current!

the value of R3 determines the set current.

Calculations:- LED current is approximately equal to: 0.5 / R3- R3 power: the power dissipated by the resistor is approximately: 0.25 / R3. choose a resistor value at least 2x the power calculated so the resistor does not get burninghot.

so for 700mA LED current:R3 = 0.5 / 0.7 = 0.71 ohms. closest standard resistor is 0.75 ohms.R3 power = 0.25 / 0.71 = 0.35 watts. we'll need at least a 1/2 watt rated resistor.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Parts used:

R1: small (1/4 watt) approximately 100k-ohm resistor (such as: Yageo CFR-25JB series)R3: large (1 watt+) current set resistor. (a good 2-watt choice is: Panasonic ERX-2SJR series)Q2: large (TO-220 package) N-channel logic-level FET (such as: Fairchild FQP50N06L)Q1: small (TO-92 package) NPN transistor (such as: Fairchild 2N5088BU)

Maximum limits:

the only real limit to the current source circuit is imposed by NFET Q2. Q2 limits the circuit in two ways:

1) power dissipation. 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 thereis a high LED current or if the power source voltage is a lot higher than the LED string voltage. (Q2 power = dropped volts * LED current). Q2 can only handle 2/3 wattbefore you need some kind of heatsink. with a large heatsink, this circuit can handle a LOT of power & current - probably 50 watts and 20 amps with this exact transistor,but you can just put multiple transistors in parallel for more power.

2) voltage. the "G" pin on Q2 is only rated for 20V, and with this simplest circuit that will limit the input voltage to 20V (lets say 18V to be safe). if you use a differentNFET, make sure to check the "Vgs" rating.

thermal sensitivity:

the current set-point is somewhat sensitive to temperature. this is because Q1 is the trigger, and Q1 is thermally sensitive. the part nuber i specified above is one of theleast thermally sensitive NPN's i could find. even so, expect perhaps a 30% reduction in current set point as you go from -20C to +100C. that may be a desired effect, itcould save your Q2 or LED's from overheating.

Step 7: Constant current source tweaks: #2 and #3these slight modifications on circuit #1 address the voltage limitation of the first circuit. we need to keep the NFET Gate (G pin) below 20V if we want to use a powersource greater than 20V. it turns out we also want to do this so we can interface this circuit with a microcontroller or computer.

in circuit #2, i added R2, while in #3 i replaced R2 with Z1, a zener diode.

circuit #3 is the best one, but i included #2 since it's a quick hack if you don't have the right value of zener diode.

we want to set the G-pin voltage to about 5 volts - use a 4.7 or 5.1 volt zener diode (such as: 1N4732A or 1N4733A) - any lower and Q2 won't be able to turn all the wayon, any higher and it won't work with most microcontrollers. if your input voltage is below 10V, switch R1 for a 22k-ohm resistor, the zener diode doesn't work unless thereis 10uA going through it.

after this modification, the circuit will handle 60V with the parts listed, and you can find a higher-voltage Q2 easily if needed.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Step 8: A little micro makes all the differenceNow what? connect to a micro-controller, PWM or a computer!

now you've got a fully digital controlled high-power LED light.

the micro-controller's output pins are only rated for 5.5V usually, that's why the zener diode is important.

if your micro-controller is 3.3V or less, you need to use circuit #4, and set your micro-controller's output pin to be "open collector" - which allows the micro to pull down thepin, but lets the R1 resistor pull it up to 5V which is needed to fully turn on Q2.

if your micro is 5V, then you can use the simpler circuit #5, doing away with Z1, and set the micro's output pin to be normal pull-up/pull-down mode - the 5V micro canturn on Q2 just fine by itself.

now that you've got a PWM or micro connected, how do you make a digital light control? to change the brightness of your light, you "PWM" it: you blink it on and offrapidly (200 Hz is a good speed), and change the ratio of on-time to off-time.

this can be done with just a few lines of code in a micro-controller. to do it using just a '555' chip, try this circuit. to use that circuit get rid of M1, D3 and R2, and their Q1 isour Q2.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Step 9: Another dimming methodok, so maybe you don't want to use a microcontroller? here's another simple modification on "circuit #1"

the simplest way to dim the LED's is to change the current set-point. so we'll change R3!

shown below, i added R4 an a switch in parallel with R3. so with the switch open, the current is set by R3, with the switch closed, the current is set by the new value of R3in parallel with R4 - more current. so now we've got "high power" and "low power" - perfect for a flashlight.

perhaps you'd like to put a variable-resistor dial for R3? unfortunately, they don't make them in such a low resistance value, so we need something a bit morecomplicated to do that.

(see circuit #1 for how to choose the component values)

Step 10: The analog adjustable driverThis circuit lets you have an adjustable-brightness, but without using a microcontroller. It's fully analog! it costs a little more - about $2 or $2.50 total - i hope you won'tmind.

The main difference is that the NFET is replaced with a voltage regulator. the voltage regulator steps-down the input voltage much like the NFET did, but it is designed sothat its output voltage is set by the ratio between two resistors (R2+R4, and R1).

The current-limit circuit works the same way as before, in this case it reduces the resistance across R2, lowering the output of the voltage regulator.

This circuit lets you set the voltage on the LED's to any value using a dial or slider, but it also limits the LED current as before so you can't turn the dial past the safepoint.

I used this circuit in my RGB Color Controlled Room/Spot lighting project.

please see the above project for part numbers and resistor value selection.

this circuit can operate with an input voltage from 5V to 28V, and up to 5 amps current (with a heatsink on the regulator)

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Step 11: An *even simpler* current sourceok, so it turns out there's an even simpler way to make a constant-current source. the reason i didn't put it first is that it has at least one significant drawback too.

This one doesn't use an NFET or NPN transistor, it just has a single Voltage Regulator.

Compared to the previous "simple current source" using two transistors, this circuit has:

- even fewer parts.- much higher "dropout" of 2.4V, which will significantly reduce efficiency when powering only 1 LED. if you're powering a string of 5 LED's, perhaps not such a big deal.- no change in current set-point when temperature changes- less current capacity (5 amps - still enough for a lot of LED's)

how to use it:

resistor R3 sets the current. the formula is: LED current in amps = 1.25 / R3

so for a current of 550mA, set R3 to 2.2 ohmsyou'll need a power resistor usually, R3 power in watts = 1.56 / R3

this circuit also has the drawback that the only way to use it with a micro-controller or PWM is to turn the entire thing on and off with a power FET.

and the only way to change the LED brightness is to change R3, so refer to the earlier schematic for "circuit #5" which shows adding a low/high power switch in.

regulator pinout:ADJ = pin 1OUT = pin 2IN = pin 3

parts:regulator: either LD1585CV or LM1084IT-ADJcapacitor: 10u to 100u capacitor, 6.3 volt or greater (such as: Panasonic ECA-1VHG470)resistor: a 2-watt resistor minimum (such as: Panasonic ERX-2J series)

you can build this with pretty much any linear voltage regulator, the two listed have a good general performance and price. the classic "LM317" is cheap, but the dropoutis even higher - 3.5 volts total in this mode. there are now a lot of surface mount regulators with ultra-low dropouts for low current use, if you need to power 1 LED from abattery these can be worth looking into.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

Step 12: Haha! there's an even easier way!I'm embarrassed to say i did not think of this method myself, i learned of it when i disassembled a flashlight that had a high brightnesss LED inside it.

--------------Put a PTC resistor (aka a "PTC resettable fuse") in series with your LED.  wow.  doesn't get easier than that.--------------

ok.  Although simple, this method has some drawbacks:

- Your driving voltage can only be slightly higher than the LED "on" voltage.  This is because PTC fuses are not designed for getting rid of a lot of heat so you need tokeep the dropped voltage across the PTC fairly low.  you can glue your ptc to a metal plate to help a bit.

- You won't be able to drive your LED at its maximum power.  PTC fuses do not have a very accurate "trip" current.  Typically they vary by a factor of 2 from the rated trippoint.  So, if you have a LED that needs 500mA, and you get a PTC rated at 500mA, you will end up with anywhere from 500mA to 1000mA - not safe for the LED.  Theonly safe choice of PTC is a bit under-rated.  Get the 250mA PTC, then your worst case is 500mA which the LED can handle.

-----------------

Example:For a single LED rated about 3.4V and 500mA.  Connect in series with a PTC rated about 250 mA.  Driving voltage should be about 4.0V.

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Comments

50 comments Add Comment view all 291 comments

 Loooser says:  Mar 18, 2011. 7:07 AM  REPLYi declare it as bullshit!

 GrumpyOldGoat says:  Mar 3, 2011. 8:25 AM  REPLYWithout going through the laborious process of reading all 256 replies dating back several years apparently...

Would a recycled computer power supply converted to a benchtop power supply do the job?

You have a complete set of tightly controlled AC and DC voltages that could be used.

I raided the dead computer repair shop and collected quite a few and tested them. Most still performed flawlessly.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

 Spuzzum says:  Mar 4, 2011. 3:16 AM  REPLYThis is exactly what I have just done.. a 350w antec, and will be spreading my led's over the 5v, 12v1, and 12v2 rails. If just using palin resistors, andsplitting up over 3.3v, 5v, 12v1, and 12v2.. I calculate 92% efficiency. That's for 127 Cree's at 350mA. But I want PWM capabilities.. so went with thisdriver. Can't run it on the 3.3v rail, but 5v and the 2 12v rails have plenty of amperage to offer. Just don't go over the maximum 10 amps the psu's 18awg wire's good for. But at 4 or 5 lines per rail, that's still quite a lot of power to be tapped. :D

I mentioned in my last post that it wasn't working on my 5v line.. it is.. must've been a ghost. And it's working with just the 100K R1 resistor as well, didn'tneed the 22K.. nor did it need the zener. At least not with the 5v and 12v sources the psu gives.

Just need to look at the specs on the psu (usually on the side, or on the site). Make sure you don't go over the maximum amps per voltage rail, and notethat 3.3v and 5v rails are "combined wattage" maximums. And some have "combined maximums" on the 12v1 and 12v2 rails as well.

As for the 10ohm 10watt "dummy resistor" needed for the bench supply mod.. I found using an led and 470ohm resistor on both the 5v and 5vsb lines forthe "power on" and "standby" led's. Uses about 1/2w. If you look on your motherboard, you'll see (or should see) a green led.. that's your pc's "dummyload". That's also connected to the 5vsb (5v standby).

For 127 led's at 700mA, I calculate about 15 drivers over the 5v and 2 12v lines.

 GrumpyOldGoat says:  Mar 4, 2011. 6:23 AM  REPLYI think you just raised my IQ by at least 2 points with that response.

THANKS My Friend. Good information to keep handy!

 Spuzzum says:  Mar 4, 2011. 1:44 PM  REPLYYou're very welcome. :)

 Spuzzum says:  Mar 2, 2011. 11:39 PM  REPLYFixed the rising current issue.. needed to tie the free leg of the trimpot to the middle leg. Everything's stable now.. and adjustable from almost nothing, to wellover 1500mA. No "set resistor" required :D.

Still won't go very high on 3.3v and 5v sources though, and I even removed the zener diode.. reading back, I noticed that was for 20v sources and higher..obviously not needed for 3.3v and 5v.

Oh well.. a 12v driver's still good enough I guess. Thanks man.........

 Spuzzum says:  Mar 2, 2011. 5:57 PM  REPLYWell, built the circuit.. with a few mods. Added both the 100K and 22K source voltage resistors, selectable by a DIP switch. This way, the board's good for10v or less, as well as 10v or more. I also used a 100K trimpot in place of a set resistor for RSense.. I want it adjustable. Problem is, anything above 300mA,and the thing just keeps on climbing.. on it's own! That's on the 12v rail of my mo'd psu. The 3.3v line won't go above 500mA for some reason.

Could it be the pot's just not rated for such a current? I used the exact n-fet and npn transistors.. local shop sells Fairchild.

Where'd I go wrong?

 Spuzzum says:  Feb 24, 2011. 4:27 PM  REPLYThe LM317K is rated at a "minimum" 1.5A, "typical" 2.2A, and a "maximum" 3.4A.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

 Spuzzum says:  Feb 24, 2011. 3:32 PM  REPLY "perhaps you'd like to put a variable-resistor dial for R3? unfortunately, they don't make them in such a low resistance value, so we needsomething a bit more complicated to do that."

I've been looking at modifying to be adjustable.. I'm thinking you can use a 10ohm 25-turn trimpot:

3299P-100LF-NDhttp://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=3299P-100LF-ND

Then use the pot in "parallel" with the other values needed to create 1000mA, then turn the pot "up" to increase the ohms, therefore lowering the current.(4x) 2ohm redistors, in parallel.. gives 0.5ohms. As long as the trimpot goes down to 2ohm.. then you just need (3x) 2ohm resistors, as well as the trimpot. 

http://www.1728.com/resistrs.htm

Sounds good anyways................ :)

 snowluck2345 says:  Feb 22, 2011. 12:48 PM  REPLYdo you think you could drive an sst 90 off of 1 18650 using this?

 phidelt85 says:  Feb 10, 2011. 11:19 PM  REPLYDan,Great read and easy to build.  However, I'm having some trouble with my build.  I used Circuit #3.  I'm powering 6- 3W Luxeon K2 Vf=3.65V.  I'm using anR3 value of .56/2W to drive the 6 LEDs at 1A.  The problem is that when I take my amp reading, I'm only getting a reading of 166mA.  I'm showing 3.3V onthe G leg of the FET.  I'm not sure what I'm doing wrong.  I get 166mA whether it's one LED or all six in series.  Any help would be appreciated.

 phidelt85 says:  Feb 11, 2011. 4:12 PM  REPLYAny help would be appreciated... Another question I have regarding the supply voltage to the FET which is currently at 3.3V, do I have to reduce the R1value in order to increase the voltage to get the FET to turn on fully?

 kmantesla says:  Feb 1, 2011. 12:43 PM  REPLYGreat instructable, I just threw this together to get the hands on experience of a current source. I designed single led desk lamp driven at just under it's maxrating 1.0A. I am very pleased with the results, and I wanted to chime in on everyone's rants on efficiency, because most people don't understand this circuitand real world efficiency. Granted, it's not the most efficient circuit in the world, but it does EXACTLY what it's designed to do, change your input to an exactoutput, keeping the leds happy and healthy.. but at a cost.. all the "changing" is converted directly to heat, not an ounce is saved.. My circuit uses a switchingwallwart; 5.2v @ 1.0A.. we can safely assume this type of adapter has an efficiency of 85%, if not more. My circuit "inputs" 5.3v @ .90A and my load, theleds get 3.0v @ .88A. Yay, this is exactly what it's designed to do, my led is nice and BRIGHT and happy, but all that stepping down and regulation doesn'tmagically convert, not with this circuit, it's converted to HEAT. So, my "regulator" circuit has a weak efficiency of about 56%, coupled with the wall adapterefficiency, the total circuit is around 50% efficient. Yikes, thats a scary number, right? But this is why we use leds, because an amateur can still be "green"even with a lossy, dirty regulator like this.. My lamp is SUPER bright, at less than 6W. I guarantee you 10 of these would EASILY rival a singular 60W bulb,in brightness and cool factor no doubt. Plus, I built mine out of spare parts, you could easily increase efficiency ALOT by designing a circuit with specificvalues on the adapter and fet.. and my led was an old rebel, newer ones are even more efficient.

Great instructable! It reignited my desire to custom build drivers over store bought ones, so I can start to really push leds, like the newer XML's to 3amps..Following this build, I immediately bought some high quality, low dropout, high EFF adjustable voltage regulators with built in buck/boost options all in aT0220 package, got them for around 2$ apiece. I currently use luxdrive's drivers for all my projects, but now I'm going to start playing around again and see ifI can come up with something just as rock steady and functional as my beloved buckpuck.

 kmantesla says:  Feb 1, 2011. 1:15 PM  REPLY-I wanted to add; people trying to calculate efficiency using any AC settings on an ordinary multimeter (less than 100$) are probably not getting accurateresults... at all... Use DC for all measurements, and estimate the mains to circuit supply adapter efficiency.. Depending on the type of adapter and load,assume it can vary as much as 65-95%.. Good AC meters and true rms meters are hundreds of dollars. If you understand them, generic meters arebasically worthless for AC measurements outside of simple residential mains checking.

 SpiffyChee says:  Jan 17, 2011. 8:01 PM  REPLYSo I'm confused about which diagram I should use for PWM with my arduino uno microcontroller. Should I use #4 or #5.Same goes for if I use a 555 chip, would i use #4 or #5?could someone please enlighten me?

 kmantesla says:  Feb 1, 2011. 12:10 PM  REPLYI'm no engineer, but in my opinion it doesn't matter too much with an arduino. Their pins can both source and sink regulated current. If you're using it setup as 5v then #5 would be easier to hook up and program. If you're forced to use the 3.3v setting or other analog stuff like a 555, then #4 is going tobetter for a full range of control, however I suck at coding and for some reason I'm pretty sure it would be a nightmare getting what I want with #4because you're going to have to use pins as inputs and outputs whereas I think #5 is a simple 5v on off situation, floating pins and imperfect code wouldnot be (as) big of a deal.

 curlyfry562 says:  Jan 18, 2011. 8:08 AM  REPLY"if your micro-controller is 3.3V or less, you need to use circuit #4"

Arduino Uno's digital out pins are 5V so you will want to use circuit #5. Same goes for the 555 as long as you are running it at 5V.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

 Asimov Andies says:  Jan 7, 2011. 1:48 PM  REPLYI understand these circuits when using the same LED's but I have 3 series of 3 LED's wired in series. 2 of those series chains have a different voltage dropacross them then the 3rd. I am assuming I need to add resistors to the front of those chains to equal out the voltage?

 acidjc says:  Dec 30, 2010. 8:11 PM  REPLYI have 10 x 10W LED, Vf = 9V and current is 600mA.

I plan to put them 2 series and 5 parallel, using a input of 24V DC,

ie. 2 x 10W in series = 18V, 600mA5 row in parallel = 18V , 3A drawn from the source

Plan to use the above "even simpler current source" on each row to limite the current flow to each row. Any problem?? do I need to change the Votlageregulator to other part?

can anyone pls kindly advise. Tks

 pmj_pedro says:  Dec 22, 2010. 3:01 PM  REPLYIf i use one of this circuits like the 5, and d the supply font is 18V, and the 4 high power leds only need 13.6V, should i use a resistor or something to not burnthe leds?

 larams says:  Dec 19, 2010. 6:51 PM  REPLYDoes the power dissipation of R3 depend on how much of a voltage drop there is? He says .25/R3 will tell us what wattage we need but doesn't really saywhere the .25 comes from. Does that formula change depending on the supply voltage?

 dan says:  Dec 22, 2010. 1:28 AM  REPLYP = V^2 / R. V across R3 is constant at about 0.5.

 larams says:  Dec 19, 2010. 7:15 PM  REPLYDoes the value for R1 matter in circuit #5?

 dan says:  Dec 22, 2010. 1:26 AM  REPLYnot much, 10k should work.

 Electroinnovation says:  Dec 12, 2010. 10:11 AM  REPLYWhere can i buy a current set resistor (labeled as R3)?

 popeyescu says:  Aug 10, 2009. 3:59 AM  REPLYHi Dan,

it seems that the link to "555 circuit" doesn't work. Do you have a schema/link for this circuit?I found another schema for 555: http://www.dprg.org/tutorials/2005-11a/index.htmlIs it good?

Thanks

 vmankal says:  Dec 8, 2010. 12:27 AM  REPLYYou can find the 555pwm ckt here:http://www.pcsilencioso.com/cpemma/555pwm.html

 Trimaran says:  Dec 3, 2010. 12:08 PM  REPLY5V zener was not enough in my case. I got 0.17 ampers while i should have get .32 according to my configuration and with one 5V zener, so I thoughtmaybe mosfet was not working normal with 5V gate voltage and put 2x5V zeners in series to make it 10V and it worked. Btw, I put them in series justbecause there was not 10V rated single zener in my stock.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

 conntaxman says:  Oct 7, 2010. 7:06 PM  REPLYQuestion about a 20 watt led.I just got a 20watt led ,it's the type that has about a 1 inch square back plate with the +and- on each side.It's13-15 volts draws14 to 1700 ma.or 1800. I bought a wall wart that puts out 14.5vdc. I have ran this on 12 volts ,it ran good. I hooked it up to the wall wart, with a 1 ohm res. inline. It was nice and bright [white in color] had it on for about 30 seconds and them moved it alittle and then the led went Dim a little bit.Say it started out at1500LM and then went to about 1200lm,This was all in about 45 seconds. The next day I turned it back on and all the Small leds[20 of them] were lite but stilldim.Would anyone know what happened to the led?My last test showed it still was drawing 1.7 am;and 14.5 volts dc. It still lights.but dimmer ,kind of like if you hooked it to 12 vdc.ThanksJohnI know when you blow them out they Don't work. lol I have done that.

 kjjohn says:  Aug 7, 2010. 6:33 PM  REPLYIn the schematic, the LEDs appear to be wired in series. I have multiple 3v 700mA LEDs, but a 3.7v power source, so I would like to wire the LEDs inparallel. So do I calculate the R3 value for 700mA * the number of LEDs?

 switch62 says:  Sep 25, 2010. 8:25 PM  REPLYYou should not put the LEDs in parallel.  It sounds good in theory, but there is no control as to how much current each LED will draw.  You will onlycontrol the total current.  That means that if one of the LEDs starts to draw a little more than the others it could overheat and then blow.  If that happensthe current in the other LEDs will rise, the circuit keeps pushing the same current, and they will all eventually die.

In your case I would recommend a separate driver for each LED.  Circuit #1 would work but may not give 100% brightness.  If you had 4.5-6V you couldguarantee 100% brightness.  At a few dollars each it would be the cheapest and easiest solution.

The other option is to use a boost driver to raise the 3.7V to something higher.  The LEDs would be in series.  The required voltage would be at leastNumber of LEDs x LED Voltage.  So 4 LEDS at 3V = 12V  the currrent setting would be 700mA.  Unless you can find a suitable design to build you'llneed to buy one.

 damidb says:  Aug 24, 2010. 10:15 AM  REPLYhello, I have a problem using dan's interesting LED circuit for a high power led. (I want to use it as a better lighting source then a bulb for my microscope,using a 3W LED 3,2V 1000mA). I included the circuit as png file so you know what i'm talking about. I first simulated the circuit with LTspice IV simulationsoftware (see other picture). The problem: Dan mentioned on instructables: "The combination of R1, R2 and R4 set the output voltage (= LED brightness) ofthe regulator. the output voltage is approximately equal to: 1.25 * (1 + ((R2+R4) / R1))." So I calculate with my chosen values R2, R1 and R4 (this is apotentiomter from 0 to 2.2 KOhm) as output voltage for the voltage regulator: 1,25 * (1 + ((3188 + 2200)/3580)) = 3,13 V But in LT spice simulation (see .pngpicture) the output voltage from the voltage regulator is quasi constant and independent from R4 (R4= the potentiometer) (see picture please) and about1,48V. instead of 3,13 V. I checked everything. What did i do wrong ?? Or is the simulation software LTspice wrong ? thanks in advance for any answer.

 letniq says:  Aug 7, 2010. 4:44 AM  REPLYHi, Great article but I didn't understand how to calculate the how many ohm should be R3. For example I'm having 36 3W power leds. 12x3 leds Source: 12VPC PSU LED Forward: 3.2V LED Current: 750mA I will have 9A through Q2 (IRF3205) Q1: 2N3904 R1: 110K It will be great if someone can help me.Thanks.

 curlyfry562 says:  Jul 25, 2010. 10:27 PM  REPLYThanks Dan, just whipped up #1 and it works great. One note: The FQP50N06L FET was out of stock at both Mouser and Digikey, so I subbed in theFQP30N06L. I think the only difference is that I can't handle as much continuous current. I never plan on drawing over 10A so it is not a problem.

 curlyfry562 says:  Jul 25, 2010. 10:39 PM  REPLYHere is one in action. You guys may recognize the LED array

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

 chikoroll says:  May 27, 2010. 6:36 AM  REPLYhey mate, i want to hook up a 25watt LED to my car

the voltage is 13-14vmy battery runs 12v (car off) and 13.6v (alternator charging)

would this be acceptable to run direct from battery, or should i run a dc-dc converter

the link is what i'm looking at

http://cgi.ebay.com.au/5-PC-BRIGHTEST-25W-WATT-HIGH-POWER-WHITE-LED-1400-Lumen-/390118430163?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5ad4ded5d3

 grimgroper says:  Jun 1, 2010. 9:39 PM  REPLYim planning to make a lighting array with similar to this

www.visionxoffroad.com/led/xmitter/

with similar 10w LEDs

cgi.ebay.com/ws/eBayISAPI.dll

i chose 10w ones because they are more cost effective as it seem that the higher power in watts for each unit they get less efficient, also easier to findlenses that i can use.

im also struggling to find out the right way to power them, as i believe the power in a car battery can range from 11-16v (because of cranking,charging...etc) so im not sure how to go about making a power supply i would also like to make one or 2 rather than 20 separate ones for each LED. imactually starting to lean towards using 3w LEDs like the xmitter, as its easier to get the right lenses.

just some things to think about, let me know how you go.

 curlyfry562 says:  Jul 17, 2010. 8:44 PM  REPLYTo avoid the varying voltage issue, I think you could add a 12V voltage reg before the current reg, granted you will need a meaty heatsink on it if yourvoltages are varying that much. Can someone check me on this

 Cairie says:  Jun 16, 2010. 8:58 PM  REPLYI only want to have ONE Luxeon 1W, how should I change this schematic?

 grimgroper says:  May 17, 2010. 4:33 AM  REPLYany ideas to run 20 10w 12v LEDs off in a car i want to run them around 700-900mA?

 mertg says:  May 4, 2010. 4:55 AM  REPLY Ok. I have a question about this topic. Some people posted comments about this circuit, being not so efficient. I want to ask them, how to measure theefficiency. I built this circuit with an IRF630MFP  and a C3198 from my old CRT monitor chasis.  I put 2 ammeters. 1 for LEDs, 1 for the whole circuit. If Iapply 12 VDC and drive 3 PowerLEDs with 349mA, I read 351mA from the ammeter connected to the main supply. The FET is not connected to a heatsinkand no heat is produced on the FET. It supplies constant current for leds. Thus can I calculate the efficiency like 349/351 ???

 mertg says:  May 4, 2010. 5:34 AM  REPLYI think I've missed some points. if i calcutale P_in and P_led (P_led / P_in) it becomes 3,35Watt / 4,2 Watt. Thus the circuit is 79% efficient. Is thatcorrect?

Thank you.

 godofal says:  Apr 20, 2010. 4:32 AM  REPLYwow, great instructable!this is really something il keep faved for future use, its really neat, handy, and all in 1 place! (instead of being scattered in 20 instructables, by 15 ppl, with alltheyr own tricks and tips :D )

thnx for this, its really helpfull!

 ac-dc says:  Jan 11, 2008. 8:50 AM  REPLYThis is another very lossy circuit, not what one would want to use to power an LED except as a good learning exercise about linear regulator control. Asxsmuft mentioned other regulators could be substituted but I would suggest using an LDO, Low DropOut type as you then don't need as high a supply inputvoltage. However there is a problem with this circuit. Suppose 3 x white LED at 3.6V forward and 1A current. That's 10.8V total and at up to 28V input to theregulator we have 17.2W of heat!! That is a very unrealisticly sized heatsink and in fact any use with linear regulators driving 1A LEDs would require a largerassembly and more costly heatsinked cooling strategy. In other words, it's just too lossy. It might be a better way to hack together a circuit for driving a fewencapsulated 100mW (~ 20mA) LEDs instead of high powered 1-3W LEDs.

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/

 dan says:  Jan 11, 2008. 12:00 PM  REPLYif you want to maximize efficiency you need to use the correct number of LED's based on desired input voltage. for example if you have 24V input, thenuse 6 LED's in series to minimize loss.

 ac-dc says:  Jan 11, 2008. 2:07 PM  REPLYAgreed, but in most situations this is the reverse of the way things work out, that one has X # of LEDs they need, and Y PSU voltage to work with todrive them.

 cahillicus says:  Apr 19, 2010. 3:10 PM  REPLY ac-dc, you regularly chime in about loss and efficiency.  What would you recommend as an alternative?  I was looking into the STCS1 from SMTElectronics used in another instructable.  That is until I realized the IC itself was 2 x 3mm.  I can't work with components this small.  All the otherIC drivers I found suffer the same flaw.  I need something I can build with my hands and a soldering tool, not a commercially fabricated PCB, amicroscope, and re-flow oven.  Seriously, I am killing myself to find a do-able driver.  

I am trying to run 12 1 watt LEDs with 3.7Vf off of a 12v motorcycle @ 900 mA. I realize I will probably have to have 4 drivers each running 3LED's.  Please, any suggestions for an electronic noob?

 Yakumo says:  Apr 11, 2010. 1:59 PM  REPLY@DanI don't know how to say it but the Instructable was a little bit confusing even if the schematics are easy to understand. Please don't get me wrong but the"parts used" and "setting the current!"-part are the most important and its kind of hidden in this much extra information. ordering the textparts a little bitdifferent will make it easier for the reader ... I think^^Thanks for the Instructable made me read a lot about stuff I didn't understood before oh and my LED's are actually emitting light now ^^

@Everyone who caresI replaced Q1 with an IRF1010N (because of the lack of Fairchild FQP50N06L in the German market) and Q2 with a 2N3904 (hat too much lying around)and it works nicely

 zspzs says:  Mar 31, 2010. 2:31 PM  REPLYDear Dan,Thanks for the article!I would like to use your current regulator to provide 5A. (For a DC motor.)Based on the above calcularions in my circuit R3 should be 0,1 Ohm / 2,5W.Should I modify anything else or that's all?Can I use 2N5089 instead of 2N5088? The supply voltage is 18V.Thank you in advance for the answer.Peter

 Orikson says:  Feb 10, 2010. 10:31 AM  REPLYHey there,

First of all, I guess the symbol for Q2 is wrong. You write, that you are using a N-channel FET, but in the scematics there are p-channel FET symbols!

Also I'm trying to build this circuit, but it isn't working as I expected. I'm tried a 100k and 1M for R1, 0.85 Ohm (5 watt) for R3 (should be around 600mA),white power LED (3,4 - 3,6V @ 700mA), BD548C for Q1 and IRL540N for Q2 because I already have them. The power supply was a regulated powersupply.I set it to 5 Volts and set the current limiter to 100 mA which I increased slowly up to 600mA.

The problem is, that the voltage wasn't regulated by this circuit! In the end the LED got 4 V at 550mA!

So where is the problem? My Q1 and Q2 seems to have nearly the same technical data, don't they?

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