High efficiency, 2μsec switching capability and compact size allow LEDs to replace incandescent light sources in theater-class DLP Projectors & architectural lighting.

Linear Technology’s high-powered synchronous step-down DC/DC converter is an excellent example of how the solid-state lighting market has matured enough to encourage smart semiconductor makers to introduce specialized products that address specific markets. Capable of delivering up to 20A continuous and 40A in pulsed mode, their LT3743 has been designed specifically to address the needs of high-end DLP projectors but its efficiency (up to 95%) and compact size should win it lots of designs in high-powered architectural lighting systems and industrial lasers as well.

Solid-state light sources have started to enjoy popularity in lower-powered consumer-type video projectors where a HBLED simply has to pump photons through a transmissive LCD array, but things get more complicated in the high-powered DLP systems that theaters use. The LT3743 has several important features that allow engineers to design a cost-effective system to replace the rotating color wheel and energy-hungry lamps used in today’s DLPs.

In Linear’s system, each of the RGB light streams is supplied by a separate LED array, eliminating the bulk of the color wheel assembly – not to mention 1-2kW worth of heat from the projector bulb! This is made possible by the ‘3743’s clever dual-loop switching circuit that gives the driver a 2 μsec rise and fall time across its entire output range, allowing precise output control at all brightness levels. The dual-loop control scheme can be used to quickly switch between on and off or toggle between two pre-programmed high and low power states. Besides allowing the LEDs to switch quickly enough to cycle through the DLP’s RGB sequence, the output second level can be used for precise color mixing to make up for any spectral deficiencies that the other two LED arrays might have. According to linear, this capability will allow DLP systems to deliver color quality that rivals celluloid.

If 20 W worth of solid-state photonic brilliance is still not enough for you, it’s possible to gang two ‘4743s together in current-sharing mode to deliver up to 40W. In pulsed-mode operations, you can double the power levels for both single and dual-device configurations for outputs of up to 80W. Despite the high power levels, most applications will cause the ‘4743 to dissipate around 2W, a power level that can be easily dissipated via the copper foil layers in its tiny host PCB –and with only passive cooling techniques.

The 20A demo board pictured here measures 25x25mm², making it easy to tuck into even the most compact projector. In fact, the demo PCB is about the same size of the inductor alone used by competing solutions. This is because Linear’s device has a much higher PWM operating frequency (1 MHz) that requires a much smaller inductance value than its competition which typically operate at 200-300 kHz.

For obvious reasons, Linear has taken a device-agnostic approach to designing its driver and says it works equally well with nearly any high-output LED or solid-state laser on the market. That said, they have apparently done some collaboration with out Luminus - makers of the Phlat Light LED assemblies. I don’t know much about Luminus but I expect to dig into them shortly. Their white and RGB LED products seem to have some of the best lumens/W I’ve seen and appear to be designed to make them exceptionally easy to use

The same high power, compact physical footprint and device-agnostic characteristics also makes the LT3743 a great candidate for many other high-powered LED applications including architectural lighting and driving those honking-big IR lasers used for industrial applications. There’s not time to go into these in detail here but you can expect I’ll be posting some of Linear’s application notes on these topics in the near future. I’ll also be bugging them for some design-oriented articles to publish in this community. You should also keep a lookout for some very educational video-based application notes I’m working with Linear on posting here.

The LT3743EUFD is available in a 28-pin 4mm x 5mm QFN package, whereas the LT3743EFE is available in a thermally enhanced TSSOP-28. Pricing starts at $4.80 and $4.95 each, respectively in 1,000-piece quantities. Extended temperature versions, or “I” grades, namely the LT3743IUFD and LT3743IFE are also available. Pricing starts at $5.65 and $5.82 each respectively in 1,000-piece quantities. All versions are available from stock. For more information and full specifications visit the LT3743’s product home page by clicking here.