Power-converter IC targets dimmable Leds, needs no optoisolator

Last week a reader posted a question on the article, Power-converter IC targets dimmable Leds, needs no optoisolator, asking, “Can anyone explain why Led lighting needs isolation from the AC line? Incandescents require no such isolation; why burden LEDs with this?” My understanding was that it was aUL rule, but before I pushed the “submit” button on my reply, I decided to ask the folks at iWatt. Here’s iWatt’s reply:

"The US Department of Energy's Energy Star program does not mandate the use of isolated or non-isolated led drivers for offline led lamps. The LED lamp manufacturers are free to use isolated or non-isolated LED driver designs. [However, a] heat sink is often used to take away heat from the LEDs. The heat sink is generally made of metal and is exposed to the user. If the LED driver is not isolated then the heat sink must be insulated from the mains voltage for reasons of safety. Adding insulation can reduce the effectiveness of the heat sink because the heat sink is not mated directly to the heat generating LEDs.

“Moreover, if the heat sink is floating, i.e not electrically grounded, then it can radiate RF noise resulting in high EMI. As such, non-isolated LED driver design can make thermal management and EMI control quite complex and challenging. If the LED driver is isolated using a transformer then the heat sink can be thermally mated to the LED substrate on the low voltage secondary side and can also be grounded to reduce EMI. Isolated LED drivers can in effect improve thermal efficiency, reduce EMI and reduce the cost and complexity of LED lamp designs that use heat sink."

So, as the LED replacement bulbs start flooding in with varying levels of performance and reliability, there’s another feature to look for, along with lumens, lifetime, color temperature, power factor, etc: Is it electrically isolated?

Power-converter IC targets dimmable Leds, needs no optoisolator