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.
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.