Sunday, November 18, 2012

3 Watt, 5 Watt LED DC to DC Constant Current Driver Circuit

The following article provides a simple yet very decent solution for driving powerful LEDs rated at 3 watt or 5 watt. These LEDs are able to produce highly intense and powerful light outputs, however these are extremely vulnerable too with their operating parameter. Let's learn 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.

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:




106 comments:

  1. could you please make some modifications for a 6 volt input????

    ReplyDelete
    Replies
    1. The shown design will work for 6V also, you may have to tweak the 400 Ohm resistor a bit for getting exactly 3.3V output

      Delete
    2. Dear Sir,
      I want a circuit diagram to run12 numbers of 3W LED's using AC current...rep pls

      Delete
    3. Dear Vinod, cmake three strings each having 3 LEDs and a series 6omh/1watt ersistor.

      put these 3 strings in parallel and connect their common ends to a 12V/2amp smps adapter.

      use heatsink for the LEDs,

      Delete
  2. Dear Sir,

    This is Naresh from Hosur, Tamilnadu. Your blog is really very much usefull. and i made this circuit it is working very fine. Pls upload more LED circuits.

    Thanks

    ReplyDelete
    Replies
    1. Thanks Naresh...I'll keep posting more LEd circuits.

      Delete
  3. Thank u very Mr. Swagatam. It is very useful blog. Pls. provide any solar related desings. Thank u.

    ReplyDelete
    Replies
    1. you are welcome jayaraju, please refer to this ink:

      http://homemadecircuitsandschematics.blogspot.in/p/solar-projects.html

      Delete
    2. 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.,

      Delete
    3. Thanks Jayaraju,

      you will see all these circuits in my blog very soon.

      Delete
    4. Thank u. Pls. just inform me when u post that.

      Delete
    5. I'll inform you when it gets posted.

      Delete
  4. Dear Sir,

    This is Guruh From East Java Of Indonesia. Your blog is really very Cool.
    Pls upload more LED circuits. like Driver For "Cree XML-T6 or U2" etc,

    Thanks

    ReplyDelete
    Replies
    1. Dear Guruh,

      Thanks for the nice suggestion, I'll try to update the article soon.

      Delete
  5. can the power source be a 9v battery, will it be able to run two or three 3 watt leds, from the 9v battery

    ReplyDelete
    Replies
    1. 9v battery should be rated at 10 ah, then it would work

      Delete
  6. The first circuit is far better than the second as the characteristic voltage of an LED falls with temperature rise. Driving with constant voltage as in circuit 2 could allow thermal runaway. The first circuit has the LED current passing through the voltage stabilising element for the LM338 and the transistor affects the voltage divider thus reducing the output voltage if the current increases. A constant current circuit.

    ReplyDelete
  7. Hi Sir, Can I use LM317?
    Thanks , Regards

    Kapila.

    ReplyDelete
    Replies
    1. Hi Kapila,

      it can be used for 3w LEDs but not for 5 watt LEDs.

      Delete
  8. Hi Sir

    This is Kapila
    Thanks a lot sir,
    And I have another problem.If I need to connect 3W X 3 LEDs in series what are the value of resisters, Power supply is 12V/5A SMPS

    ReplyDelete
    Replies
    1. Hi Kapila,

      for 3 in series just change the 400 ohms resistor with 1K+680 ohms resistors in series, that is a 1680 ohms resistor

      Delete
    2. 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?

      Delete
    3. 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

      Delete
  9. What will be the Efficiency ???

    ReplyDelete
  10. Hi
    am Dipu frm kochi......
    I need a circuit for connecting a 5w LED to AC 220 v.
    waiting ur reply
    dipumichael@gmail.com

    ReplyDelete
  11. Hi,
    I need a circuit for connecting a 5W LED to a 220 v line
    dipumichael@gmail.com

    ReplyDelete
    Replies
    1. you can use a 12V/2amp smps in conjunction with the first circuit shown above...

      Delete
  12. I need a circuit for connecting a 5W LED to a 220 v line

    ReplyDelete
    Replies
    1. you can use a 12V/2amp smps in conjunction with the first circuit shown above...

      Delete
  13. I would like to use 9v batt to run this circuit on my mountain bike, any modification? Please advice.

    ReplyDelete
  14. How can I run 3x1w led using this circuit? I'm using 9v batt, Any suggestion I can run with 9v batt?

    ReplyDelete
    Replies
    1. 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.

      Delete
  15. Where in India do you get cree led's and where do you get led optics for led's in india. either address or web store published would be helpful to diy-ers.

    regards

    mandar

    ReplyDelete
    Replies
    1. I am sorry presently I have no info regarding it.

      Delete
  16. I am trying for 10 watt LED light at 12Volts/ 800mA.
    What are heatsink requirements and how to solve it.
    I have mounted it on 2 x 2 inch heatsink but after a while
    it become hot enough. Moreover the LED emits high intensity
    light which I feel damaging for eyes. How it can be diffused?
    and what material you suggest. ***I like your circuits, Best wishes***

    ReplyDelete
    Replies
    1. 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..

      Delete
  17. 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

    ReplyDelete
    Replies
    1. 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.

      Delete
  18. 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

    ReplyDelete
    Replies
    1. 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.

      Delete
  19. Hi Mr Swagatam,

    Your blog is very useful. But I need to connect 5W X 3 LEDs in series, so what are the value of resistors? I use 12V/5A SMPS as power source.

    Thanks in advance.

    Tommy HG

    ReplyDelete
    Replies
    1. Hi Tommy,

      What's the operating voltage spec of each LED?

      Delete
    2. The spec of each LED says:
      mA max.: 1500 mA
      V type.: 3 V
      V max.: 4 V
      Reverse Voltage: 5 V
      Watt: 6-7W

      then which one of your circuits I have to use, the first or second?
      Thanks for your help Mr. Swagatam

      Tommy HG

      Delete
    3. 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.

      Delete
    4. I have built the circuit...It's work! Tested for more than 5 hours, so far it's stable neither too hot with proper heat-sink on LM338 and LEDs

      Thank you Mr Swagatam.

      Delete
  20. 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

    ReplyDelete
    Replies
    1. Hello Krishna,

      Please refer to the following post, you will get an idea of the required procedures:

      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-high-watt-led-current-limiter.html

      Delete
  21. Can you Please upload the Schematics for Isolated Constant Current 6W, 8W and 12W SMPS used for LED drivers?

    ReplyDelete
    Replies
    1. You can use the following two circuits together to fulfill your requirements:

      http://homemadecircuitsandschematics.blogspot.in/2012/03/how-to-make-simple-12-v-1-amp-switch.html


      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-high-watt-led-current-limiter.html

      Delete
  22. 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.

    ReplyDelete
    Replies
    1. 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

      Delete
    2. Ok. noted. thanks.

      one more question, is there specific Watts value for resistor or can i use any watts value?

      thanks.

      Delete
    3. 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.

      Delete
  23. 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.

    ReplyDelete
    Replies
    1. 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

      http://homemadecircuitsandschematics.blogspot.in/2013/07/making-led-halogen-lamp-for-motorbike.html

      Delete
    2. 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.

      Delete
    3. an alternate circuit can be seen below with all the necessary formulas:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/make-hundred-watt-led-floodlight.html

      Delete
  24. 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 ?

    ReplyDelete
    Replies
    1. 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

      Delete
  25. I forgot to ask what the power ratings are for the resistors in this circuit ?

    ReplyDelete
  26. 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..?

    ReplyDelete
    Replies
    1. 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.

      Delete
  27. 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

    ReplyDelete
    Replies
    1. 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.

      Delete
    2. how bout 5V 6.5amps or maybe 12V 5amps???

      Delete
    3. 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.

      Delete
    4. 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?

      Delete
    5. please tell me the operating voltage of the LEDs, i'll provide you with the required data.

      Delete
  28. 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

    ReplyDelete
    Replies
    1. 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



      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-high-watt-led-current-limiter.html

      Delete
    2. noted. will give it try and let you know of the result. many thanks

      Delete
    3. btw i want to get it right... R1 is the 400 ohms resistor or is it the 240ohms?

      Delete
    4. The discussed R1 is in the following post, pls don't confuse it with the above post:

      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-high-watt-led-current-limiter.html

      Delete
    5. oh ok, last question before i proceed. where will be the placement of R1?

      Delete
    6. 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:

      http://4.bp.blogspot.com/-cQYYHQMayYc/UX4km7_cniI/AAAAAAAAEDQ/oYsD49dla0w/s1600/lm196+pinout+details.png

      Delete
  29. noted and wish me luck... thanks

    ReplyDelete
  30. Hai swagatam, your blog is awesome. I am following it. I made a water tank controller from ur blog. Its working great. Thank you. Now I am planning to make LED pannels for my home. If I connect ten 3watt LED in parallel means how much amphere should i need??
    and how to calculate it??
    LED specifications:-
    Forward voltage = 3.5v
    Forward current = 700mA
    Power dissipation = 5w
    Please help...

    ReplyDelete
    Replies
    1. Thanks Sriram,

      3.5 x 0.7 = 2,45 watts, so it cannot be 5 watts

      10 in parallel would require 10 x 0.7 = 7 amps.

      Delete
    2. So if i connect ten 3 watt LEDs in series means how much amphere should it require??

      Delete
    3. in that case current will be 700mA, but voltage will need to be 12V

      Delete
    4. How it wil be 12v ?? 3.5v per LED. If i connect ten LEDs in series means i need 3.5 x 10 = 35v. If I am wrong means can u pls explain me pls???

      Delete
    5. yes it will be 35V, I confused it to be 3 in series.

      Delete
  31. Can u pls provide me ur contact mail id??? so I can clarify doubts regarding my LED panel for home.

    ReplyDelete
  32. I made a LED panel by placing four 1watt LED in series fixed on 4x4 inch 1mm aluminium sheet. Like that two panel connecting in parallel. This panel will work with motion sensor. Now I like to make a power supply and backup for that. The panels need 14vdc, 700mA and the sensor circuit need 5vdc. Please provide me a smps circuit for the follwing specification:
    1. The circuit's input should be a AC main connection.
    2. I need two outputs from the circuit. One should be 5vdc and another should be 14vdc, 700mA.
    3. Battery backup should be there in the circuit for both output. so if AC main supply is there means , the light panel and the sensor should work with the AC main supply. Suppose if AC main power failure occurs means, instantly the sensor and the pannel should work with the battery backup.
    4. Then if AC power supply comes means again the output should work with AC supply only and battery should start chraging.
    5. The battery should contain overcharge protection.
    6. The backup time should be 2-3hrs. so what volt and amps of battery i need??
    Thankyou in advance...

    ReplyDelete
    Replies
    1. Sriram,

      for the SMPS you can try the following circuit:

      http://homemadecircuitsandschematics.blogspot.in/2012/03/how-to-make-simple-12-v-1-amp-switch.html

      adjust R6 to get 14V

      for the automatic actions you can make the following design:

      http://homemadecircuitsandschematics.blogspot.in/2013/02/make-this-automatic-10-watt-to-1000.html

      just replace the shown transformer power supply with the 14V SMPS given in the above link.

      Delete
  33. Thank you for ur quick response.... I am having one doubt... Suppose My LED panel needs 14v, 700mA. But if I connecting 14v, 2Amps battery to the LED panel means, wil it affect the LED panel lifetime due to the higher Amps from the battery? or the battery backup wil increase??

    ReplyDelete
    Replies
    1. if the voltage does not exceed the forward voltage of the LEDs then current will not matter....however if the ambient heat increases the situation could become dangerous, so use of a current controlled supply is recomeneded, for example using a LM338

      Delete
  34. Hello sir,
    I need a 12v to 28vdc converter 3w/5 w. Want to light up 5 led of 1 each.
    I have seen an ic circuit but the manufacturer has rubbed the number on it. So plus can u help me with an alternative circuit or anyone knows which ic is used in this kind of circuit

    ReplyDelete
    Replies
    1. Hello Akshay,

      You can try the circuit given in the following link:

      http://homemadecircuitsandschematics.blogspot.in/2012/09/led-emergency-light-circuit-using-boost.html

      Delete
  35. Hi Swagatam! Really amazing blog and such simple circuits. Appreciate the effort you put in.

    1) If I want to drive 6 x 1 watt leds, should I connect them in series or parallel? Also do I need to make any changes in the above constant current circuit?

    2) Instead of 6 x 1 watt leds, if I want to drive 3 x 1 watt leds, what changes should I make in the above circuit?

    ReplyDelete
    Replies
    1. Hi Vimal, thank you! Due to a large number of comments the replies occasionally get delayed, although I try my best to finish them quickly.

      Answering to your question the series or parallel specifications will depend on the voltage level that you are using.

      How much voltage do you have or intend to use? Please provide me the data I'll let you know how to proceed with it.

      Delete
  36. Hi Swagatam! Posting this again because my first post simply disappeared! Really amazing blog.. appreciate the hard work you put in to keep this blog buzzing.

    Regarding the 3 Watt, 5 Watt LED DC to DC Constant Current Driver Circuit,

    1) If I need to run 6 x 1 watt leds from this circuit, what changes do I need to make in the circuit? The input voltage shall be from 12 volt car battery.

    2) Instead of 6 x 1 watt leds, if I decide to run 3 x 1 watt leds, what changes should I make to the circuit?

    Thanks...

    ReplyDelete
    Replies
    1. Hi Vimal,

      Thanks once again, OK got it, here are the answers:

      1) make two parallel strings each having 3 LEDs in series, change the 400 ohm resistor in the first circuit to 1.68K and use 1 ohm resistor for the bottom most resistor

      2) for 3X1 use a single string having 3 LEDs in series, the 1.68K will not change, but the above 1 ohm will now become 2 ohms.

      Delete
    2. Thanks ! Will try it and let you know how it works out.

      Delete
  37. Hello Swagatam,

    I have tried doing circuit 2 on this page for 4 x 3.3v 700ma leds in parallel, circuit works and is great with my resistor values being R1 =270 and R2 being 440 but the LM338 is getting extremely hot, i have a heatsink attached to it but it gets hot to point of it hurts to touch.

    700ma x4 = 2800ma so it's well within it's current tolerance, so why is it getting so hot?

    Regards,
    Emile

    ReplyDelete
    Replies
    1. Hello Emile,

      yes, even though 2800 may look within it's range, these linear ICs tend to generate a lot of heat.

      The remedy could be to use higher voltage and to put the LEDs in series, this would greatly reduce the current as well as the heating up of the IC.

      for 4 LEds you could use a 4 x 3.3V input meaning a 15V input so that all the LEDs could be wired-up in series, requiring just 700mA for the entire series.

      Delete
  38. sir can i use LM317? with last circuit for one no 3W led. what will be the wattage of 240ohm and 400 ohm resistors.?

    ReplyDelete
    Replies
    1. yes you can use the last circuit, the wattage of the resistors will be 1/4 watt...

      Delete
  39. sir but red green blue white 3w leds having various voltages. red-2.8v, green,white & blue 3.8v,
    my question is 240ohm, 400ohm is suitable for any color 3w led?

    ReplyDelete
    Replies
    1. Which LED do you want to want use exactly,

      the 400ohm will set the output to 3,3V approximately

      you can alter the 400 ohm resistor accordingly using an online LM317 calculator.

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.