LED drivers are making that glow happen

LEDs are showing up everywhere, no doubt of that. Over the past decades, they have migrated from merely being solid-state replacements for basic incandescent and neon bulbs indicators, to being used in backlighting, large-scale signage, and even area illumination.

And why not? They have many advantages in terms of their efficiency, lifetime, and form factor, as well as other attributes. But the less-recognized hero—and sometimes critical factor—of LED installations is the LED's driver, which takes AC or DC rails voltage and efficiently delivers it as a properly managed current to the LED. As LED opportunities become more widespread and technically diverse, the drivers have to be tailored to "make it so."

What we're seeing in 2011 and into 2012 are new LED drivers carefully focused on the specific needs of low- , medium-, and high-power applications, at low to high voltages, and for individual and group LEDs. In other words, we have met the market, and its name is diversity

For example, street lighting is a non-glamorous but very attractive opportunity. But unlike the LED, which is a current-driven, low-voltage-drop component, street lamps run from 120 Vac minimum, and many have power lines as high as 480 Vac. In addition, any power supply usually needs line-to-load isolation for user safety. To support this specialized situation, several vendors have announced LED drivers which have the requisite hooks needed, as well as other fault-tolerant and safety-centric features.

Wide-area and room lighting is another hot application, but again, has its unavoidable constraints. The physical construction of the light fixture (called a luminaire in the trade) is often at odds with the thermal demands of the LED die, which gets extremely hot despite its luminous efficiency. (Unlike the incandescent bulb, which radiates its waste heat, the LED keeps it in the die area.) This lighting application also often needs dimming, which is now usually implemented by a Triac-based circuit, which implements a version of PWM.

Dimming and LEDs presents a different challenge. The simple way to dim is to cut back on the current, but that brings unsatisfactory LED illimination in terms of color consistency, linearity, and dynamic range. Further, LED drivers do not mesh well with the huge installed base of Triac dimmers. So LED driver vendors are addressing dual opportunities: ICs that provide LED-compatible dimming, using constant-current drive levels with PWM control for new installations, and Triac-friendly drivers for the dimming units in already place.

Single-unit LED installations are not the only part of LED-based systems that have specialized requirements. Strings and arrays of LEDs are used for backlighting, and large-area screens and signage, which means that the drivers have to be able to support series, parallel, or combined series/parallel configurations. For very-large arrays, these drivers also have to implement various types of LED control, multiplexing, and addressing.

What's does it all portend for 2012? More vendors entering the market, as they see the huge growth and opportunities (and maybe even the possibility of proclaiming their contribution to the "green" message); vendors assessing how they can bring their expertise in high DC/DC converter efficiency, low quiescent current, or high-voltage design and process to drivers; more second- and alternate-sourcing of the more basic driver ICs; and increased fragmentation of drivers offerings as they target unique application niches.

Wait a moment: the diversity and application-optimization of LED drivers are starting to resemble their analog cousins of op amps and A/D converters. The more things change, the more they repeat themselves.

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