AC LEDs - a solution for many problems?

September 28, 2012 // By Christoph Hammerschmidt
One of the advantages of LEDs over competing lighting technologies is their longer operational life. In many cases, the driver electronics have become the limiting factor. But drivers a no longer needed, said experts at the LpS LED lighting symposium in Bregenz. Powering LEDs directly from AC mains is not only possible, they said. And it would resolve a number of problems.

The idea is simple: Since an LED inherently is a diode itself, its properties as a diode could be used to get rid of all the electronic circuitry. Bob Kottritsch, Vice President of Lynk Labs advocated the idea of AC-powered LED lighting. In its most simple form, two antiparallel strings of LEDs could be connected directly to the mains outlet. Switched in serial, their total forward voltage needs to meet the line voltage. Likewise, the added reverse voltages across each single LED must not exceed their breakdown voltages - in other words, if one simply switches enough LEDs in series the array will become compatible with the mains voltage. "This would greatly simplify the design of LED lighting installations since the power supply would become redundant", Kottritsch explained. "It is not so much a technology but more a topology issue". Bridge, hybrid and other more complex arrays of LEDs could be created to adopt the installation to the specific requirements.

Driver-free AC LEDs would not only be cheaper and more reliable than today's LED-driver combos, they would also be dimmable in today's prevailing phase-cut infrastructures. Kottritsch said. Neverheless, there are challenges: Thermal density is one of them - the LEDs could not so easy be operated at their efficiency sweet spot. "And one would need significantly more LEDs for a given lighting proect", Kottritsch admitted.

Some experts in the industry favour the idea of driverless LEDs. LED manufacturer e:lumix, for instance. The company has developed a LED chip structure with "inherent overload protection" explained CEO Thomas Zabel. "LEDs with this semiconductor structure could be used as a building block for driverless AC LEDs".

Not all insiders hail the idea of driverless LED lighting. For instance driver manufacturers are not so amused about this idea. Stephan Gruber, CEO of LED driver manufacturer Exscitron GmbH, does not believe that this idea will have a great future. "A regulated switching power does not