Linear's New Lumens

Linear Technology continues to grow its family of LED drivers to specifically address the demands of merging LED requirements. The LT3799 provides the first compact, single stage, isolated LED driver with active PFC. Tony Armstrong, Linear's Director of Product Marketing for Power Products, took me through the latest release. Linear's LT3799 can operate from the universal input range of 90VAC to 265VAC; the high voltage end of the specification is limited only by external components at this time, and can power high brightness LEDs requiring from 4W to over 100W. This is head-and-shoulders above the high-end limit of other products in the industry and will find applications where high levels of lighting need to be installed while retaining high efficiency of operation. Such applications can be found among stadiums, parking garages and offices. It uses a unique single stage flyback topology which does not require an optocoupler and offers a PFC of 0.98 and very low harmonic distortion. The LT3799 isolated LED controller with its active power factor correction (PFC), is specifically designed for driving LEDs from the universal input range (90VAC to 265VAC) with the huge advantage of enabling the use of fewer external components resulting in a significantly reduced footprint size than conventional techniques. The LT3799, optimized for LED applications requiring 4W to over 100W of LED power is also compatible with standard TRIAC in-wall dimmers. This is an important factor for system designers and takes away the nightmare scenario of back-fitting key components in an upgrade situation. The LT3799's unique current sensing scheme delivers a well regulated current to the secondary side without using an opto-coupler. This not only reduces cost, but also improves reliability. Its single stage PFC regulator design requires minimal external components. Additionally, it's thermally enhanced MSOP-16E package ensures a simple and compact solution footprint for off-line LED applications.

As the power saving capability, long life and other benefits of high brightness (HB) LEDs continue to drive the development of a wide range of lighting applications it is no surprise that the growth rate of LEDs continues to accelerate. In order to continually expand the wide base of applications, LED drivers must continually improve to leverage all of the benefits that LEDs offer. Arguably one of the most widespread emerging applications will be operating HB LEDs from offline AC power. Applications range from replacement bulbs to completely redesigned smart lighting systems. In the USA and Asia, offline power is generally 110VADC, while in Europe it is 220VADC. Using an AC voltage source to power HB LEDs introduces several new challenges for IC drivers. First, LED drivers must offer high efficiency to preserve the energy savings inherent of LEDs while minimizing costly heat sinking. Accurate Power Factor Correction is also important in maximizing distribution efficiency while simultaneously minimizing harmonic distortion. Additionally, electrical isolation is required for safety and reliability and to facilitate easy system design and upgrade, lighting systems have to be compatible with existing circuitry such as TRIAC in wall dimmers. Finally, LED based lighting solutions must not only offer enhanced power savings and reliability, but must also be compact, simple and costs effective.

The LT3799 offers over 86% efficiency, eliminating the need for external heat sinking of the LED driver IC in most applications. Special internal circuitry provides active PFC of up to 0.977, easily meeting industrial Department of Energy (DOE) requirements while also complying with the IEC 61000-3-2 Class C Lighting Equipment Harmonics requirement. The LT3799 can be used with a standard in-wall TRIAC dimmer without any visible flicker. Open and shorted LED protection ensures long-term reliability for a wide range of LED applications. Summary of Features: LT3799

• Isolated PFC LED Driver with Minimum Number of External Components
• VIN and VOUT Limited Only by External Components
• Works with Standard TRIAC dimmers
• Active Power Factor Correction
• Low Harmonic Content
• No Opto-Coupler Required
• Accurate (±5%) Regulated LED Current
• Open & Shorted LED Circuit Protection
• Thermally Enhanced 16-Lead MSOP Package

The LT3799EMSE is available in a thermally enhanced 16-pin MSOP package. An extended temperature version, or "I" grade, the LT3799IMSE is also available from stock. As with all Linear's announcements, I suspect this is not by any means the end of the story and that we'll soon be hearing of more innovations in this key area. For more information, visit www.linear.com