LED DESIGN FORUM: A three-stage power supply efficiently drives multiple LED strings (MAGAZINE)
A PFC stage, an inverted constant-current buck regulator, and a downstream DC/DC transformer circuit can drive LEDs with better than 90% efficiency says JAMES ALIBERTI.
Higher-power LED lighting applications such as street lights, high-bay stadium lighting and others favor multiple-string architectures for a multitude of reasons, including ease of design, flexibility and safety. The main engineering challenges are efficiency, long life and uniform light output, to name a few. Long life and higher efficiency play a critical role in the overall value proposition in LED lighting systems as they are needed to reduce costly maintenance occurrences.
The most popular approach to multiple string architectures is to purchase an off-the- shelf power supply with a power factor corrected (PFC) front-end with an isolated constant-DC output voltage where the output voltage feeds a regulator for each LED string. To maximize efficiency, the preference is to use buck regulators and a power supply with the highest possible DC output that is still within Class II or SELV maximum voltage levels of 60VDC. For this approach, I recommend using a 36V or 48VDC output as they are ordinary off-the-shelf power supplies commonly used in telecommunications applications.
This article was published in the May/June 2010 issue of LEDs Magazine. To read the full version of this article, please visit our magazine page, where you can download FREE electronic PDF versions of all issues of LEDs Magazine. You can also request a print copy of LEDs Magazine (available by paid subscription) and sign up for our free weekly email newsletter.