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Led buck converter schematic Answered

I have been looking for a led buck converter schematic for quite some time now and i haven't been able to find one that suits my needs. i have a single 3 watt led that i believe needs 700ma to run. My whole purpose for the converter is to dim the led so it will have a longer battery life. i'll run it off of some rechargeable batteries that i can remove. Also i would like to be able to purchase most of the parts fairly easily.

The requirements of the buck converter.
-Battery powered
-Capable of powering a 3w 700ma led

This is a link to the data sheet of the led:

Thanks in advance

3 Replies

Jack A LopezBest Answer (author)2016-07-17

Previously I mentioned there exist DC-to-DC converter modules available via eBay, and I wanted to show you one of them, which can be used for driving a 3 watt LED.

Also a circuit diagram for this module is attached. I did not draw this. I found this drawing in a discussion on this page,

See also

and I found these pages via a Google image search for "XW026FR4", which is a word printed on the module itself.

If you want to find this module on eBay, the phrase to search for is "LM2596 converter", or similar words, since this module is based on the LM2596 IC.

Of course you can look up the data sheet for the LM2596, using www.alldatasheet.com, or Google(r), or whoever is your favorite data sheet aggregator, and that data sheet will, of course, include some circuit diagrams too.

Anyway, what remains is for me to show you some pictures of this gizmo working as a 0.3 A = 300 mA constant current source. Two pictures are attached.

When setting the constant current and constant voltage set points, I use a test-load (in this case a 5 ohm resistor, which is actually two 10 ohm resistors in parallel) that cannot be harmed by pushing too much power through it. Once I am confident the regulator is actually working as a constant current regulator, then I swap out the test load for the white LED.

The red boxy meters are set up in ammeter mode. As can be seen from the pictures, the regulator module is pushing 0.3 A through the test-load ( a 5 ohm resistor) in one picture, and pushing 0.3 A through a white LED in the other picture.

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Downunder35m (author)2016-07-11

If it is a 12V system you can check for 3W LED lamps for caravan use ;)
Simply discard the included LED's and use it for your LED.
Some that I opened and re-puposed only had a simple buck converter to get a set voltage and a single resistor to limit the current - not ideal but working good enough to be produced by the thausands in china....

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rickharris (author)2016-07-11

If your LED is rated at 3 watts and has a suitable heat sink it should have a life of 20,000 hours or more - i.e. several years.

A "simple" current regulator will do what you want. Like the illustration - click to see bigger. for dimming make R1 a vairable resistor.

Select a suitable current for your LED (something less than 700mA)


lots of choice. - Your LED will no longer be 3 watts of course = Watts = Volts x amps.

so 3 watts at 700 mA = around 5 volts.

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