The following article provides a simple yet very decent solution for driving powerful LEDs rated at 3 watt or 5 watt.
Circuit Objective
These 3 watt 5 watt and similar high watt LEDs are able to produce highly intense and powerful light outputs, however these are extremely vulnerable too with their operating parameter. I have explained more how to operate these devices very safely using a simple power supply.
We have seen quite many power supply and driver circuits in this blog using the IC LM338, that's because this particular device is so versatile with power regulation and control functions.
The same IC yet again takes the center stage in this application too. Here the IC LM338 has been configured in its standard mode and it perfectly executes the expected current as well as voltage regulations for driving a 3 watt or a 5 watt LED.
Circuit Operation
As shown in the circuit diagram below, in its standard mode the resistor 240 ohms is a regular placement, and the next resistor connected to it is the one which decides the voltage at the output of the IC. Here it has been calculated and set for producing around 3.3V at the output, which is the optimal voltage value for driving all types of white LEDs.
However the IC itself cannot control the current and normally would allow about 5 amp at the output.
We can see that the IC is associated with an additional active component which is the transistor connected to its ADJ pin.
The transistor here is employed solely for controlling the current at the output to the specified limits.
The resistor across ground and base decides how much current would be allowed to the output.
As indicated in the diagram, 0.6 ohms will pass about 1 amp maximum current which becomes suitable for driving a 3 watt led safely, and if a 5 watt LED needs to be driven safely, this resistor must be replaced with a 0.3 Ohms, which will allow a maximum of 2 amps of current.
The input to the IC can be derived from a standard transformer bridge capacitor power supply or from a suitably rated battery supply.
In fact, the transistor and the associated base/emitter resistors are absolutely not required, because once the voltage is set to precise 3.3V, the current would automatically get adjusted as per the LEDs specs.
So the correct circuit should be as given below:
Update:
The above suggestion is not recommended if the ambient temperature is above 25 degrees Celsius. Therefore users are requested to go with the first universal design using the BC547 as the current limiter stage, for enabling the intended current control function.
LED Driver Request
The following request for a customized 9 watt LED driver with constant current was requested by one of the avid readers of this blog
We need constant current LED driver. Supply in put is 11.0 vTO 15.0 vdcOut put required is constant current 1400 mA, 8.4VDC. The Load is 3 White Power LEDs, having Vf - 2..7 to 2.8V. This cluster will operate in flashing (Blinking mode). The circuit should have utmost high reliability, minimal number of components. We were using ONSEMI Linear LED Driver NSI 50350AST3G, (qty. 4 nos. connected in parallel)which is now not available Can you please suggest us some suitable Part or Circuit?
The following circuit diagram was suggested for the above application:
Questions & Answers
I would like to use 9v batt to run this circuit on my mountain bike, any modification? Please advice.
How can I run 3x1w led using this circuit? I'm using 9v batt, Any suggestion I can run with 9v batt?
if you are using 9V PP3 battery, then it won't work, it should be rated at least at 4AH.
With a 9V fixed supply you won't require any circuit or resistor, simply put the LEDs in series and connect it directly to the battery.
I am sorry presently I have no info regarding it.
Use a bigger heatsink, it's as simple as that. Try increasing the size until it prevents any further rise in the heat.
If you diffuse it you would reduce the amount of light from it, so it's better not to look at it, which is a dangerous thing to do anyway..
hi
i want 5 x 1 watt blue led to be put in this circuit,
does it require any change in components…
and can i put a solar panel of 12 volt 5 watts as the input,,,
pls guide me
Use the first circuit and connect the lEds in parallel at the output, use a 0.5 ohm resistor in series with each LED and select 0.3 ohm as the current limiting resistor as shown in the circuit.
Thank u very much Mr. Swagatam. I am trying to implement those circuits. Pls. send some more links for the real time circuits which is useful for solar applications like solar converter for existing normal inverter, solar charge controller for different amps, solar LED driver circuits, solar lanterns 3w,5w circuits, etc.,
Thanks Jayaraju,
you will see all these circuits in my blog very soon.
Thank u. Pls. just inform me when u post that.
I'll inform you when it gets posted.
Hii…
Your blog is real cool.
i had a doubt regarding the forward voltage of the 5W LED. I thought it was 7V at If=700mA instead of 3.3V.
can you please provide the specs. or link to the datasheet of the LED used here..?
regards,
joseph
Hi thanks,
Different manufacturers may provide sightly different specs, one says it's around 4.5V as given here:
http://www.lumex.com/images/Lumex_New2w_3w_5w-HPleds.pdf
No issues, you can set the voltage as required by simply adjusting and selecting a different value for the 400 ohm resistor.
Hi Tommy,
What's the operating voltage spec of each LED?
You can use the first circuit.
If you are connecting the LEDs in series, replace the 400 ohm resistor with a 1.68K resistor, or a 1k and 680 ohm in series.
the vertical resistor at the bottom should be replaced with a 0.4 ohm 1 watt resistor.
you are welcome!
Hello Swagatam Majumdar sir,
i want to install 2X3Watt 12 volt Led lights as a my bike Pilot lamps (parking lamps), i want the 12 volt constant current regulator for these leds please give me the Driver, thank you.
if possible please forward the details to my mail id chkrishnachaitanya9@gmail.com
Hello Krishna,
Please refer to the following post, you will get an idea of the required procedures:
https://www.homemade-circuits.com/2013/06/universal-high-watt-led-current-limiter.html
Can you Please upload the Schematics for Isolated Constant Current 6W, 8W and 12W SMPS used for LED drivers?
You can use the following two circuits together to fulfill your requirements:
https://www.homemade-circuits.com/2012/03/how-to-make-simple-12-v-1-amp-switch.html
https://www.homemade-circuits.com/2013/06/universal-high-watt-led-current-limiter.html
Hi,
Can you please give the resistor value (ohms & watts) for 2 led in parallel?
what is the recommended capacitor volage for 12-14v circuit?
Thank You.
Hi, if you are using 12V then you should connect them in series.
Use 1.2k resistor in place of 400 ohms, rest of the values will be as it is
Ok. noted. thanks.
one more question, is there specific Watts value for resistor or can i use any watts value?
thanks.
divide the wattage of the LED with supply voltage and multiply the result with 0.6, this will give you the wattage for the lower resistor, remaining will be 1/4watt rated.
Hello sir,
I want to install my home 1w high power led's in series connection, using 12v 7.5 AH lead acid battery. Please give the method. Thank you sir.
Hello Vedha,
Please refer to the diagrams provided in the following article, you can try them for your application, the input should be from a 12V 3amp smps AC/DC adapter
https://www.homemade-circuits.com/2013/07/making-led-halogen-lamp-for-motorbike.html
Sir,
1.Alternate method for changing LM338 Voltage Regulator.
2.Give the instruction 12 or 15 (4*3 or 5*3) led bulbs connections in the 12v 7.5 AH lead acid battery.
an alternate circuit can be seen below with all the necessary formulas:
https://www.homemade-circuits.com/2011/12/make-hundred-watt-led-floodlight.html
Lot of thanks sir.
You referred me to this page. I mentioned in my previous post that I wanted to convert a 110V 10W LED floodlight to 12VDC and also have the ability to flash as an emergency light. MY question is, this article is for a 3W and 5W LED. Can I still use it for my 10W LED and do I need to change any of the components ?
You did not mention 110V in your previous comment, you said that the LED had a forward voltage of 12V and current rating of 1amp and you wanted to operate it at a little lower current than the given max specs.
Anyway, here's what you need to do in the first circuit:
replace the 400 ohm resistor with a 1.8k, 1/4 watt resistor
replace the bottom most resistor with a 0.66 ohm 1 watt resistor
as already mentioned in the previous comment, you can use a standard IC 555 astable flasher circuit and connect its pin#3 with the collector of the transistor in the above circuit. connect pin3 via a 1N4007 diode, cathode should be connected to pin3.
Whenever you switch ON the 555 circuit will result in the flashing of the LED
I forgot to ask what the power ratings are for the resistors in this circuit ?
Hi There, Mr.Kapila and Specially Mr.Swagatam!
Sir if i need to connect these 3w X 3 LEDs in parallel then which type of modificatons to be required?
Hi Muhammad, you can use the first circuit from the above article, no changes would be required except for the bottom most resistor which should be replaced with a 0.2 ohm resistor
hi sir i want to create a led lyts for my farm .. i want to connect 30 leds in parallel my problem is that i have 12volt 200amp battry when im trying to connect leds to battery they are going to be hotter what should i do brightness is very awsome but why they are going to be hot..?
Nizamani, you will need to fix the LEDs on a large aluminum plate so that the heat from the LEDs is sinked and dissipated otherwise the LEDs will get damaged within minutes.
While fixing the LEDs on the aluminum make sure the leads do not short with the aluminum plate.
Good day sir i want to connect 5 pcs of 3Watts leds to this circuit of yours please guide me thank you… power supply will 9v 1700mah
Good day thurrmac,
1700mAH will not support even one 3 watt LED properly, 5pcs is out of question, you may require at least 5AH input for it.
how bout 5V 6.5amps or maybe 12V 5amps???
yes will do, in that case you can make the first design from above, you will need to calculate the parameters as per the given instructions.
unfortunately sir i dont have any background in electronics im not able to calculate. what would be the best position of the leds is it in series?
please tell me the operating voltage of the LEDs, i'll provide you with the required data.
here are the data of the leds.
3 Watts
DC forward Voltage: DC 2.8-3.8V
DC forward current: 700mA max
Rated power: 2.66W max
you can use 4 in series with a 12V input and use LM 338 as a current limiter as shown in the following post, R1 will be around 2 Ohms 1 watt
https://www.homemade-circuits.com/2013/06/universal-high-watt-led-current-limiter.html
noted. will give it try and let you know of the result. many thanks
btw i want to get it right… R1 is the 400 ohms resistor or is it the 240ohms?
The discussed R1 is in the following post, pls don't confuse it with the above post:
https://www.homemade-circuits.com/2013/06/universal-high-watt-led-current-limiter.html
oh ok, last question before i proceed. where will be the placement of R1?
across the "out" and ADJ pins of the IC, it's clearly shown in the diagram.
for pinout details of LM338 you may refer to the following image:
4.bp.blogspot.com/-cQYYHQMayYc/UX4km7_cniI/AAAAAAAAEDQ/oYsD49dla0w/s1600/lm196+pinout+details.png
noted and wish me luck… thanks