National Semiconductor has announced its linear LM3466 LED driver that’s designed to power a string of LEDs in street and area lighting applications, requiring only a resistor and capacitor in terms of external components. The new Micrel MIC4801/4802 drivers are designed to power a single LED at 600 mA and 800 mA respectively for solid-state lighting (SSL) in architectural or landscape applications.
The National LM3466 LED driver is designed for use in a typical street-light design where a switching constant-current AC/DC power supply must drive multiple strings of LEDs. Multiple LM3466 drivers would operate in parallel in such a scenario taking the constant-current input with each driving one LED string.
Generally, switch-mode power supplies offer superior efficiency to linear power supplies and an LED driver is basically a power supply. But National claims several advantages for the linear option in a multi-string street light with a separate AC/DC power supply. The linear driver creates no switching noise. Manson Chan, Principal Product Marketing Engineer at National Semiconductor, said, “There is no interference emitted from a linear regulator which simplifies the system design and saves the cost of an EMI filter.”
Chan also asserts that the efficiency of a linear regulator matches or exceeds that of a switching regulator in the case of a string driver powered by a separate AC/DC supply. He said, "The LM3466 can go up to 99% in efficiency.” Moreover, Chan says the linear driver eliminates the need for magnetic components saving both money and space.
The LM3466 integrates a MOSFET that can drive LED strings with stack voltages as high as 70V. External components can allow the driver to handle even greater voltage levels.
The driver can output current up to 1.5A, and only an external capacitor and resistor are required to configure the device. In a multiple-string application, a control bus allows the parallel drivers to equally or ratio-metrically allocate the drive current. If a string fails with an open circuit, the other drivers in the system can automatically equalize the current throughout the operating strings to maintain constant output power.
LED driver for architectural lighting
The cause for a linear regulator in applications such as architectural and landscape lights as envisioned by Micrel is simplicity. The MIC4801/4802 LED drivers are designed to operate from a low-voltage input such as 5V and to generate a constant-current output for a single LED.
The linear design eliminates switching losses associated with typical boost converters. The Micrel drivers also eliminate the need for an inductor and offer the benefit of no EMI noise.
The drivers offer 1% accuracy in terms of current regulation to ensure uniform illumination. An external resistor is used to set the current level.
Moreover, the drivers include what the company calls an Ultra Fast PWM Control interface. A microcontroller or other PWM controller can control the brightness setting of the driver down to a duty-cycle setting of 1%.
Micrel also recently introduced a six-channel linear LED driver – the MIC4811/4812 – designed for lighting billboards, marquees and other large-scale applications. Each channel drives a single LED at either 50 mA (MIC4811) or 100 mA (MIC4812).
Other recent driver news
In other recent driver news, Analogic Tech introduced the AAT1451 LED driver that targets display backlighting applications. The IC can drive four LED strings at up to 93% efficiency. “Power management considerations for system designers vary depending on the size of the display and the use-case scenarios they are targeting," said Ray Chan, Technical Marketing Manager of AnalogicTech. "With the AAT1451 we bring to market the most comprehensive feature set available in an LED driver that makes it possible for batteries to last longer, a critical differentiator in the rapidly growing tablet market.”
For engineers working on retrofit lamps, Marvell has teamed with Philips Lumileds to create a manufacturing-ready reference design based on the former’s 88EM8081 driver IC. According to the companies, the reference design for a 6.5W LED replacement for a 40W incandescent can cut four to six months from the typical product design cycle. The design utilizes Philips Luxeon A LEDs. Marvell has also created reference designs for 40W-equivalent A-lamps and 100W-equivalent PAR38s in partnership with Cree.
