Introduction: High Power LED Driver Circuits

Picture of High Power LED Driver Circuits

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 . 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.

Step 2: Power LED Performance Data - Handy Reference Chart

Below 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 putting them 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 drop
red/orange/amber: 2.5V drop

Luxeon-3 with 800mA current:
white/blue/green/cyan: 3.8V drop
red/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 drop
green/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 also to 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 how much 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 burns out 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.


- 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 the LED 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 reason the LED Throwie works so well.

Step 4: The Humble Resistor

This is by far the most widely used method to power LED's. Just connect a resistor in series with your LED(s).

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

- 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 LED performance.
- 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 circuit and resistors for you!

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

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 Regulators

Switching 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? the switching 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 it constantly 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.

- 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

- 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 quite happy with it. these devices are available from most of the LED web stores.

Step 6: The New Stuff!! Constant Current Source #1

Picture of The New Stuff!!  Constant Current Source #1

lets get to the new stuff!

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

- 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

- 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 only costs $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 at the 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 maximum efficiency, 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 the only downside of this circuit compared to a step-down switching regulator!

setting the current!

the value of R3 determines the set current.

- 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 burning hot.

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.

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 there is 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 watt before 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 different NFET, 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 the least 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, it could save your Q2 or LED's from overheating.

Step 7: Constant Current Source Tweaks: #2 and #3

Picture of Constant Current Source Tweaks: #2 and #3

these 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 power source 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 way on, 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 there is 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.

Step 8: A Little Micro Makes All the Difference

Picture of A Little Micro Makes All the Difference

Now 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 the pin, 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 can turn 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 off rapidly (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 is our Q2.

Step 9: Another Dimming Method

Picture of Another Dimming Method

ok, 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 R3 in 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 more complicated to do that.

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

Step 10: The Analog Adjustable Driver

Picture of The Analog Adjustable Driver

This 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't mind.

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 so that 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 safe point.

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)

Step 11: An *even Simpler* Current Source

Picture of An *even Simpler* Current Source

ok, 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 ohms
you'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 1
OUT = pin 2
IN = pin 3

regulator: either LD1585CV or LM1084IT-ADJ
capacitor: 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 dropout is 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 a battery these can be worth looking into.

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 to keep 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 trip point.  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.  The only safe choice of PTC is a bit under-rated.  Get the 250mA PTC, then your worst case is 500mA which the LED can handle.


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.


Chon Fai GeorgeL (author)2017-07-28

I was looking the for a constant current LED driver circuit the other day so that I can understand the principle of LED driver. I had so many bad experience with the existing LED driver in the market, and I want to know why.

I am very fresh into electronics, please excuse my ignorance if I say something fundamentally wrong.

I did some study with the circuit and the part list. At first I thought the Q1 (N channel enhancement mode MOSFET) is supposed to operate at ohmic region which was regulated by the Q2 (NPN type BJT); however, I looked at the MOSFET data sheet, and it seems the resistance fluctuation due to the current flow from drain to source of the MOSFET is not sufficient make a difference (I used a 60V DC supply, with 300mA LED load as design parameter and size everything accordingly).

After some calculation, it seems that the only thing the MOSFET does is to stop the circuit with excessive current flow (on the order of 10 to 50 times the running current), and does almost nothing to the small current fluctuation.

Once again, I am very new to the electronic circuit design, and maybe I've interpret the datasheet incorrectly. I am hopefully I can get some insight from the experts like you concerning a little more detail about the calculation and the detail parts selection.

Thank you.

FredW55 (author)2017-06-16

for option # 5 in step 8, can someone give me a components list/breakdown? I am having some trouble following along with the full instructible and don't want to order parts I don't need.

Also, is there a tutuorial here anywhere that informs how to calculate the ratings needed for each of the components based on voltage/amperage of the LEDs being driven?

lantieau3 (author)2017-06-13

Will the second Micro Controlled circuit still work if the NPN transistor is replaced with an NFET?

Pankaj0718 (author)2017-05-19

In cuircuit 10..can u plz tell the value of capacitor & value of resistance R1,R2,R3, & pot R4...i want to use 3watt power white led....

kamhagh (author)2017-05-03

20$?! I bought a step down with current limiting for like 1$ it has no problems with 1a (I have a 10W LED)!

TheFireMan (author)kamhagh2017-05-16

Realize this Instructable is 10 years old.. prices on some electronics have gone WAY down.. $20 to $1 is not uncommon......

fpires (author)2017-03-22

In the circuit #4, when using a 3v3 uC (like esp8266 family), could a opto-coupler substitute the zener? There's any benefits on this (apart the isolation of the uC from the rest of the circuit)?

Arthurhapi (author)2017-02-16

Hi guys! Can anybody help me? Let's say, I want to choose 1 LED at a time to light-up between 3 LEDs (RGB) using a momentary push button switch, what do i need to do? Please help me.

theo1945 (author)2016-11-30

It was easy to follow you instructions, and I was able to complete the circuit. However, when I put in a 3.7v battery, the current is 470 mAh. When I insert a 9v (8.4v actual), the current goes to 540 mAh. I thought the current should be the same. If it should be the same, what might I have done wrong. The LED is a 3w on a PCB star and lights nicely using both batteries. But like I said, the current changes. Thanks in advance for any ideas on what I may have screwed up.

HardlyHumanFX (author)2016-09-22

I'm trying to find out where to start if I want to blink an LED panel at 100 times per second. Could you point me in the right direction? :)

tigraf (author)HardlyHumanFX2016-11-20

1. You need to learn "The Magic Word": PWM. Lot of resources around.

2. easiest way to do it: use 555 IC, best calculator for this:

(use datasheet to map pins and IC limitations).

2.a: use any kind of microcontroller to generate PWM signal and change duty cycle.

3. You will need to drive P- or N- channel mosfet with this PWM signal to operate with hi-power load.

johngimli (author)2016-11-18

I love the circuits and the documentation. A lot of effort went into
this and is most appreciated. Thank you very much. I was curious, and
it is only a small thing, why is the MOSFET drawn as a P-CH and not an
N-CH? Great article overall.

kamhagh (author)2016-11-01

Thanks a lot :) This sounds pretty good and reasonable for LEDs. I wonder why They sell the expensive controllers :? you can't change the voltage with them too. you can't control them with a mcu :S

computerboy_1987 (author)2016-10-04

hey how r u.

i want to make for cree xhp50 how can i make it? cree xhp50 18.8 watt

MuneebM3 (author)2016-06-28

I have a geepas tourch gfl 3854 having microchip led, using two um 1 rechargeable batteries which dims out , can i use a single 13650 battery for it?? Im afraid i would damages the led or burn it out.. Plz suggest me

MuneebM3 (author)2016-06-28

I have a geepas tourch gfl 3858 having microchip led, using two um 1 rechargeable batteries which dims out , can i use a single 13650 battery for it?? Im afraid i would damages the led or burn it out.. Plz suggest me

henry666 (author)2016-06-24

How about if i need to power up 10 led 1w, so i need up to 5amp transformator? Is that right?

Sorry my bad English im from Indonesia

tipusultan (author)2016-04-30

I want to control the brightness of 1W LED using the #4 circuit with PWM input from FPGA whose I/O pins work with 3.3V. As told in #4 circuit, I configured the output pin as "open drain". Still I am unable to get the desired results, LED stays at a constant brightness. It's brightness doesn't seem to vary with the variable duty cycle. I tried to mount the circuit on breadboard of which a picture is attached here. The right most circuit is #4 circuit.

I am in urgent need :,(. Pls help with this. Pls let me know where I am making mistakes.

Quick reply will be highly appreciable.

Thank you in advance!!

Diljitsingh (author)2016-03-29

Hi guys. I have 5 and10 watt led. Now i need a 10 watt led drive circuit. Can you please give me any circuit diagram. Please

IanJ32 (author)2016-03-22

so lets say I want to power an luxeon rebel star RGB and use an arduinos PWM pins to control the brightness and power the LED with a 7.4 volt Lithium ion battery would you suggest using a 3.3 volt 800 mA voltage regulator as well as three of you circuit 5 to limit the current to somewhere between 500-650 mA's? is there anything else I would need?

DonCesare (author)2016-03-19

Hi. The link to the 555 circuit is broken or erased. If someone could point me out to a good 555 circuit to implement with this driver would be awesome.
Thank you so much in advance!!!

Webservant7 (author)2016-03-05

I am wondering if you can help me or point me in the right direction for what I am trying to find.

I am using a 30V power source to power a pretty simple circuit that has a component which will be decreasing in resistance over time. However, I need to keep the current constant at .8 mA to 1 mA. I don't know much about electronics or how to put a circuit together so I would like to know if this circuit already exists and can be purchased. Do you know of a supply of this kind of thing?

Any help is greatly appreciated!

jakill made it! (author)2016-03-04

Hello, already a while ago, I made these 2 variants:

variant #3:

Kitchen Fume Hood Light

dimmable variant with constant voltage source:

TV Backlight

And I plan to remake this project I made a long time ago without a proper knowledge of LED behaviour (reduction of forward voltage with temperature) or even having the quality LEDs:

LED Flexible Ceiling Chandelier

The primitive circuit is attached to the comment.

Does anyone know a better (than by a primitive resistor) way I could limit the initial charging rate of capacitor? The original idea was to make a simplistic 'lossless' LED supply from 230V AC. Now I'd like to keep all the LEDs in series but apply the current limiter equivalent to variant #3 instead of the primitive 620R resistor, softening the power supply... I also prepared aluminum sockets to transfer the heat from the LED bodies to the surface of the cylindrical aluminum cases. Btw, if you're about to criticise the bottom black case, feel free to do so - I know it's ugly and I regreted the decision of not leveling it with the wooden cap immediately after completion.

XyanX (author)2016-02-05

What is Q1 if you are piloting current?

wordsforthewise (author)2016-01-25

There's also linear current regulators, but you need a PCB

wordsforthewise (author)2016-01-25

Can't we just use P=I^2*R to calculate heat dissipated by the resistor? It seems to give a slightly lower number than 0.25/R3.

dingdongding (author)2016-01-25

Hi Dan

I want to connect 3 10w led chip in parallel is it ok to buy a 30w led driver to do that or can I build one with your circuit mentioned above.Thanks for any reply.

DonCesare (author)2016-01-20

Awesome! But can Ibuse a rfp30n06le n channel mosfet? Thank you for your time and dedication.

TheThinker (author)2016-01-07

Excellent article! Just what I was looking for.

Matto70799 (author)2015-09-05


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.

Any help would be great. Thanks.

EdwardS32 (author)Matto707992015-10-27

Matto sounds like you are looking for a power supply to supply the needed input voltage and current. Did anyone point you in the right direction? You can fairly cheaply and easily make your own or you can collect "wall warts" (ac/dc adapters) from all sorts of things. If you look up "full wave bridge rectifier" im confident you will find what you need. Look for one with an isolating transformer. I am sure i have a book around here with a great schematic if you cant find one. Just message me if you are having trouble and ill get you some great beginner links. Good luck. This is one of the best fields to be involved in.

ChaseB14 made it! (author)2015-10-27

Worked exactly as described. I will put the heatsinks on when I move all this to a circuit board. I bought a pack of qty5 10w leds from ebay and they are very bright! They are dimmed on the picture so I don't overheat them. Great description on how to build.

ssharmagdr (author)2015-09-02

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.

Jonners (author)2015-08-04


Wow, great article!

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?

Many thanks,


Matto70799 (author)2015-08-03

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.

ChristopherS17 (author)2015-07-15

another thought

could I just use an extra 3W 1A bead to forward another 3 volts to the 10w chip

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

would this keep the LED's in a range where they will not try and draw more current?

also if I used 2x 500ma PTC parallel would that then handle 1amp with 2 amp cut off ?

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

ChristopherS17 (author)2015-07-13

I bought 10w LED
I believe they have 3x1w beads in series and 3x parallel runs ( 9 beads )

when combining LED's in series does their running current also increase ?

ie) if they where 1w 3.5v 350ma beads would they cut out at 1050ma ?
or would they still cut-out at 350 current and use 1050ma power ?

I had ordered 500ma PTC but now thinking I really needed something a lot lower

RamanaR1 (author)2015-06-20

I have 12v, 10w bright led, can u help me to build drive circuit from 220v

RobertK13 (author)2015-06-09

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.

KiSwiSje (author)2015-05-23

I really don't think the pptc is regulating the current. It is just protecting the battery from excessive current draw and posibly explosion.

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.

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.

I wish I had the necessary components to test this out. My 250mA pptc did not play nice with my 20mA leds :(

Clark57 (author)2015-05-02


I have a Constant Current LED driver module that I removed
from a LED grow light, rated 80-100V @ 600ma. It currently runs a 45 LED
string. It says that it’s a HP060 but it doesn’t look like anything I’ve seen
that matches that on the web. I can’t really see any of the part numbers, but
there’s a transformer surrounded by smaller components, including the only
adjustable thing, a little blue potentiometer. (I have no schematic, but I
assume this might be a “typical’ circuit.)

What I want it to do is to run a 23 string @ the same
rating. The PROBLEM is that when I do, the supply kicks the total voltage down
to equal the same voltage across each LED. Basically, I am trying to double the
voltage at the same current, but it won't let me. (The LEDs are rated at over
double their current power so I am not worried about blowing them.)

Real world:

I measure across the LED while 45 of them are on and the
voltage is 2.225VDC @ 600ma. I then short the string to 23 and measure and it
is still 2.225VDC@600ma, but I want 4.45VDC@600ma across each LED. (2.225@1200ma would do but I don’t think this
thing will do it.)

Like I said, there's a micro blue potentiometer on this
module and I don't know what it does (nor do I have a schematic) but I need to
know what to do to adjust this up to 4.45VDC.

I’m assuming there’s some kind of resistance sensing circuit going on, but I’m
looking at it and I see the transformer, a couple of what look to be SCRs on
heatsinks, a choke, three electrolytic caps (and some smaller caps, too), and
the potentiometer. I’m not comfortable randomly adjusting the pot when I don’t
know what it does.

(As well, a miniature supply that could do what I want would be considered,

I need this, like, 8 years ago so please help!


conquer (author)2015-04-22


I wish you a nice day!

We are looking for LED drivers and dimmers for project. We
have finished with wiring.

Lighting system in that project have about 450 meters of LED
strips inside aluminum profiles recessed in ceiling, separated in parts
with lenghts 0.75 m, 1 meter, 1.5 meter and 2 meters.. Also, there are parts
with individual lenghts of 5.4 m, 3.2 m.... Type of LED strip is 3014 SMD
14,4 W/m, input voltage DC 12V, 120pcs/m, pure white color. So, that is
450(m)x14,4(W/m)=6480W, around 6,5kW power of whole system at full load. Lighting system
must be dimmable and wireless controlled. I need help with choosing right LED drivers and controllers for system. You can see project in attachment.

Thank you in advance.

node-xD (author)2015-04-18

Trying to wrap my head around this and I've got a few questions that hopefully somebody can clear up.

1. " LED current is approximately equal to: 0.5 / R3."

Is he using the value of 0.5v because that is the "Vce Saturation (Max)" value for Q1, the 2N5088BU transistor? If not, where does it come from?

2. "The input voltage can be as little as 0.6 volts higher than the output voltage."

Is this also determined by the "Vce Saturation (Max)" value for Q1? If not, then where does it come from?

3. "The power dissipated by R3 is approximately: 0.25 / R3."

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?

4. "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 & current - probably 50 watts and 20 amps with this exact transistor."

Is he talking about the MOSFET burning up 50 watts on it's own, or 50 watts for the entire circuit, LEDs included?

5. Considering that the "dropout" 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? (author)2015-04-10

I've been studying and designing some modules based off of your schematics.

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?

I received my parts and can confirm that the "even simpler" takes care of the voltage difference too. :)

ozdenakca (author)2015-03-13


for step 10, how can i calculate the voltages and currents? I want to modify this curcuit for different types of power leds.

thank you and have a nice day! :)

Krolo made it! (author)2015-02-08

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.

xenonion (author)2014-11-05


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?

Thank You

theinlinaung2010 (author)2014-10-31

Hi there, this is a very good instructable with nice presentation.

I am planning to build constant current source #1.

Led : 10 W

Forward Voltage : 9-11 V.

Forward Current : 1050 mA.

Input Voltage : 12 V 5 A.

I assume R3 is 0.476 ~ 0.5 Own. Is it right?

I can't find the parts you suggested in local electronic stores. I could find only 2N2222, BC547 (Q1) and IRF640N (Q2).

If I use those transistors instead of the ones in the guide, what changes do I have to make?

AjayV1 (author)2014-10-30

your circuit is good cost effective need thermal compassion .

About This Instructable




Bio: Dan Goldwater is a co-founder of Instructables. Currently he operates MonkeyLectric where he develops revolutionary bike lighting products.
More by dan:Giant Xylophone made from Bed SlatsEasy Mothers Day Fudge (with small child)Mosaic Tile Pixel Art Car
Add instructable to: