Designers of LED-based systems may be glossing over one of the most important components, leaving their products susceptible to catastrophic failures, a circuit protection manufacturer said recently. "When you're designing LEDs, a lot of thought goes into driver efficiencies and power factors, and very little thought goes into the surge immunity standards you have to meet," Usha Patel, director of Latin American sales and segment marketing for Littelfuse Inc., a circuit protection manufacturer, said in a recent interview. "Circuit protection is like the lost stepchild. But if you do it wrong, it can kill your entire application."
Ironically, insufficient circuit protection may compromise the very reason for using light-emitting diodes (LEDs) in the first place. Many engineers specify LEDs because they offer long life and low maintenance. But both of those advantages are lost if designers fail to specify the correct protection against over-current and over-voltage situations. "LED luminaire replacements are two to three times the cost of incumbent technologies," Patel told us. "So you want it to last a minimum of five years without having to service it."
Patel breaks down circuit protection into two broad categories: over-current protection, which typically involves safety concerns; and surge immunity, or over-voltage protection, which often involves protection against lightning. "Over-voltage focuses on equipment reliability," she said. "Over-current involves the risk of shock and fire."
Both, however, can ruin an LED-based application. Voltage spikes from lightning or so-called "line swells" can ruin sensitive electronics downstream from power supplies. Too often, though, designers are unaware of the standards involved, especially with relatively new technologies, such as LEDs. Patel said:
LED lighting is a very fragmented market. There are many small companies that are trying to do the entire design, but they don't know what the standards are, or how to meet them. For many of the lighting designers, this is something new.
To know what the surge level will be, Patel recommends that designers first consider the location of the application. Indoor applications differ from covered outdoor applications, such as parking garages, and from uncovered applications, such as streetlights. "A lot of designers will buy the power supply, LEDs, heat sinks and thermal parts, then try to put it all together," Patel told us. "But the driver may only be rated at 2 kV or 4 kV, whereas an outdoor application needs to meet 10 kV."
Engineers should start considering such issues after they've picked their power supply and LED driver. That way they'll know how much current will be driven through the system and what the driver's rating will be. They can then add protection in front of the driver or as an external module. Protection is critical, not only because products can be ruined, but because unprotected systems can have safety concerns. "You need to have short-circuit protection," Patel said. "Excessive current causes heat, which leads to fire."
To deal with over-voltage situations, Patel recommends customers thoroughly understand their LED drivers, and in some cases, use transient voltage suppression (TVS) diodes. Such solutions aren't always obvious, however, especially for those who are exploring new technical territories. Patel said:
We are bailing out customers all day long. Their electronics are blowing, and they say, 'but we put in AC protection.' For some reason, though, they still have too much energy running through their circuits. It happens all the time.
Learn more at Littelfuse's Speed2Design site.