A Driver Specialist's Worldview

This UK-based engineering company moved from fluorescent ballasts to LED drivers and never looked back.

We've been discussing driver design and tradeoffs lately. Now Electronics Weekly brings us an in-depth interview with a principal engineer at Harvard Engineering, who presented a driver-centric view of the LED ecosystem.

Writer Steve Bush interviewed Harvard's Ken Dale. Harvard was started in 1993 to manufacture ballasts for fluorescent lighting, but by 2009 was designing and turning out LED drivers under the CoolLED brand in its Yorkshire, England factory. (They still make some ballasts for fluorescent and HID.)

As we heard from TI's John Perry in the recent Design News webinar, driver makers have plenty of work. Luminaire manufacturers are getting adventurous and putting together "almost every conceivable series and parallel arrangement of LEDs" and requesting suitable drivers for them, according to Electronics Weekly.

Harvard now lists 28 models of drivers up to 150 Watts, providing 250 mA to 2.1 A, with variants both for building into luminaires (integral) and for external mounting (remote). The company still makes flying lead variants, but Dale said these designs are not as widely used in Europe.

Here are a few of the points that caught my interest:

• Controls: Harvard makes drivers for use in street lighting that incorporate a wireless control scheme they call "LeafNut," which is based on the proprietary WiMAC protocol (at 868 MHz). I found it interesting that Electronics Weekly reports that the LeafNut module "replaces the photocell mounted on top of most UK streetlamps" -- which indicates a degree of uniformity in the design of street lights that is almost certainly not present across the US. For the residential market the company is developing "EyeNut," based on ZigBee, but isn't talking about the details until its drivers are released near the end of this year.
• Dimming: Harvard offers Dali and European-style 1-10V dimming. While an ANSI standard exists in the US for 0-10V dimming, the company found that in the US market it is mostly honored in the breach. Dale said:

  We started doing US products based on the ANSI 0-10V standard. But this is not what is used in general lighting in the US. In general US lighting, the 0-10V characteristic is very similar to [European] 1-10V, and one driver will meet both.

  Harvard's drivers, in common with most others today, also accommodate the majority of legacy analog leading-edge and trailing-edge dimmers.

• Efficiency: Dale claimed that the electrical efficiency of Harvard's drivers is around 88 percent, and a (not yet released) 150-Watt driver reaches 93 percent efficiency.
• Customization: because Harvard manufactures locally, they are able to meet requests for custom modifications to their standard drivers. "It is one of the strengths of Harvard," Dale said. This could mean that the company gets early exposure to trends in lighting design, as designers wanting to try something new shop around for someone who can accommodate their needs.

There is more detail in the Electronics Weekly interview and I suggest it will repay your time in reading it.

Related posts:

• The Driver's Seat: Driving LEDs
• Flicker & Its Discontents
• A Webinar on Designing With LEDs

— Keith Dawson , Editor-in-Chief, All LED Lighting