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.
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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.