Using AC With LEDs (Part 4) - the New Technologies





Introduction: Using AC With LEDs (Part 4) - the New Technologies

Some of the roadblocks in general acceptance of LED in the home has been the relative high cost per lumen and the complicated and clumsy power conversion systems.

In recent months, a number of new developments promises to bring us a step closer to a LED-powered world.

Taking its cue from the ATX system which powers our computers, a new line of "Green-mode" adapters will convert any voltage from 100v to 240v, AC or DC, to run combinations of 1- or 3-watt LEDs in numbers from 1 to 7. These modules are under 1" in length and can actually be inserted inside the base of a household light-bulb.

Here, I've chosen a conversion module designed to power a single 3-watt LED at about 700mA, but have attached it to 8 x 100-milliAmp "Superflux" LEDs in parallel, which allows me to simplify heat-sinking and light dispersion.

The entire assembly can fit on a board 1.5" on each side.

Step 1:

The module can be obtained here for about US $3.00 in single quantities, shipping included.

The 3-watt design means that there is no voltage over 5-volts on any of the LEDs, and they are completely isolated from the mains.

The large "MHX" capacitor seen in the images is used to filter the input, so its wire leads do carry high voltage. Cover them with electrical tape to be safe.

The "Green-mode" design rectifies and smooths out the mains voltage and uses it to drive an oscillator at about 100KHz. This square-wave is applied to a small flyback transformer which converts it to a much lower voltage . The currents in and out and the temperature are measured 100000 times a second and the oscillator is turned off until proper operation is restored.

Step 2: The LEDs

The LEDs I'm using here are 100mA (so called 0.5-watt) "Superflux" or "Piranha" LEDs. You can get them here.

They are able to handle this power without over-heating because cooling fins are built-in under every module.

The close-up shows sets of gold wires which go through the phosphor into 3 over-sized LED devices. Under low power, the separate diodes can be seen.

Step 3: Construction

Construction is very simple - I used a small (2" x 2") piece of perf-board. Connect all the LED Anodes (+) together, then to the Red wire of the module. Do the same thing for the Cathodes (-) and attach to the other (white) wire.

The remaining white wires are attached to AC-mains.

Step 4: The Light

I took this uncorrected composite with the white-balance set to "daylight". On the left is with a 50-watt halogen, and on the right, what it looks like with our 3-watt LED "bulb". The last picture is the same view with the LED light on the left.

Although seemingly very blue, the LED light's spectrum is almost identical to noon-day sunlight, and is what our eyes see best with. As an experiment, cover half of the picture with a piece of paper and see how fast your eyes adjust to the different light spectrum.

Step 5: Another Lighting Test

And here, the first picture under a 15-W fluorescent.

The second with the 3-watter, using the same exposure.

Step 6: Other Options

This commercial unit, also featuring 3-watts of power, costs US $20.00.
However, the beam pattern is definitely Spot, so room lighting is not its strong point.

Ours can be built in an hour or so, for about $10 in parts.
And it provides soft, even lighting for the entire area.

Again, exposures are identical, uncorrected and set for 'daylight'.

This is a continuation of my "Using AC with LEDs series", see my previous articles for background on this technology. Part 1, part 2 and part 3.

More information about constructing LED circuits can be found on my website here.



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    107 Discussions

    Hi qs can I know if I am using 3x3W LED driver constant current at 600mA. How many superflux LED do I need and how to layout them. Thanks.

    2 replies

    Usually, for 3*3W units, you need to have 30-35 parallel strings of 3 or 4 20mA white LEDs in series, or about 120 pieces. For red and amber, you will need even more, 6 in series. Note that all LED strings must be identical and preferably from the same manufacturer/batch.

    To be safe, use the specified output voltage range and divide it by 3.3v (use 2.2v for IR, red, yellow and orange). Round it up to get the minimum number of LEDs to connect in SERIES. Then take the output current and divide it by the operating current through each LED. It is advisable to use 15mA for multiple LED setups like this, and to maximize the higher efficiencies of the LEDs at this current.

    Note that with 120 LEDs, you can direct drive off mains. For 110v, just connect 2 rows of 60 in opposing polarities. For 220-240v, a simple bridge using four 1N4002 will drive an entire chain of 120.

    please provide the designing details

    Stupid Q # 362 ....I want to build some of these, but want to use them in existing 115 VAC lights, regular, not floods there a screw type base that I could use for this project?

    2 replies

    Is there a reason you went with 8 LEDs instead of 6 or 7 seeing as the output from the driver is 650 - 700 mA?

    3 replies

    Better esthetics? :)

    Seriously, the lumen/watt output of LEDs go down the harder you drive them - a complete reversal to what we've learned with incandescent bulbs.

    So, not only would 8 LEDs allow me to run things a bit cooler, it actually produces a tiny bit more light than 7 LEDs would!

    I want to drive 80 x 100-milliAmp "Superflux" LEDs in parallel. Do you know if DX has a driver for that? Also, any suggestions on all parallel or series-parallel is appreciated.

    If you are particular as to the exact number of LEDs, a far simpler (and efficient way is to hook 50 to 65 of them in series and put them on a rectified AC source. If you are on 220-240v AC, then you can direct drive 100 to 120 of them. See my previous 'ible here:

    WHOAAAA!! So the amount of light between the 8x100mlA and the 1X700mlA is practically the same? of course as you pointed out, eight LEDs have better heat dissipation and light dispersion than just one. Will these particular LEDs used in your project fade after some usage? As long as you match the rate of 700mlA of this converter, you could use any LED type (red. green, etc) in its given quantities, right? I HAVE SEEN THE LIGHT!! :-)

    9 replies

    No - in parallel circuits you cannot mix your LEDs. Each LED has to share an almost exact percentage of the total, and, if the Vf of one is substantially lower than the others, it will 'hog' all the current and basically self-destruct.

    Alright, I won't do that. Let me see if I understand the basic then: in this project's case, you used 8 matching LEDs to fulfill the converter output. Why 8? because that's the needed number according to their own power requirements to fully cover the 700 mlA of the converter. Now, if I get other color LEDs, green, red, amber, superbright white, etc, their own power requirements changes, but if I use ONE type of color only (all red, all green, all amber, etc) using your formula I will get a number of LEDS to fully cover the 700 mlA of the converter. I guess I should have made clearer my question by adding that as long as I fully cover the output (mlA) of the converter, I could use any number of the SAME LEDs on the array safely. Not different LEDs within the same array, but different color arrays instead. (thanks for the warning, though ;-] ) What could be your considerations in the following case: -Let's say you want to place the converter in the middle of a room, but you want to place the LEDs around the corners of such room. Distance between converter-LED will increase of course, therefore its internal resistance. You will have to consider the length/diameter of LED wires, but where this r (ohm) value fits within your formula? Thank you, qs, for your explanations and this instructable. I fave'd it. Cheers!!

    Yes, as long as the 8 (or 9!) LEDs share the same electrical requirements, and add up to 700mA, or MORE, then you should be fine.

    The advantage of splitting up 700mA into smaller 80mA lights is that the current loss is 100 times less (Ploss = i*i*R), so thinner wires may be possible. Probably #26AWG wire if the distance between lights is under 10-ft.

    Nice instructable. Thanks.

    When you say "add up to 700mA, or MORE" does that mean greater than 9 superflux LEDs? Can 20 superflux LEDs be used on the single controller?


    In essence, since the device is Current-limited and the LEDs are connected in parallel, you can have any number of LEDs which can handle at least 700mA. With 9 LEDs, the current going through each will be about 78mA. Although this doesn't sound like much, remember that for LEDs, light output per amp goes up as the current goes down. In other words, light production is more efficient if we drive it with a lower current.

    Thanks for the response.

    Do you think I could use your AC design connecting (4) of these in parallel?


    No - the two are not compatible! The design you indicated is meant for a constant voltage source, like from a fixed output wall-wart. It uses resistors to burn up power which will otherwise over-drive the LEDs.

    Supercool! QS FOR PRESIDENT! (after Obama, of course.) Thanks again and keep the great work man!

    As far as the light output goes, more sources tend to give more even illumination - like the different between a 'naked' bulb and a frosted one. There will be a slow reduction in light output - the 10- or 100,000 hour life is based on the point at which light output is exactly half of when it is new. Most of this is caused by heat, so make sure everything runs cool and you'll get the service you expect from LEDs.