Tuesday, October 30, 2007

National Semi Introduces Common-Anode, Current-Mode, High-Brightness LED Driver With PWM Dimming

Source : Click here
National Semiconductor Corp. introduced what it describes as the industry's first common-anode, current-mode, high-brightness light-emitting diode (LED) driver with pulse-width modulation (PWM) dimming. The LM3433, a member of National's PowerWise® energy-efficient product family, drives high-power, high-brightness LEDs in backlighting, projector and solid-state lighting applications.

National's LM3433 LED driver is said to open the way for high-reliability LEDs to be used in large-screen liquid crystal display (LCD) television (TV) backlighting applications where a common anode approach offers a thermal advantage. In another example, the company claims that LEDs can be used in today's shrinking "pocket projector" designs for a wider color gamut, higher reliability and longer life expectancy than the ultra-high performance (UHP) lamps used today.

Luminus' PhlatLight LEDs are a new class of LED for very high-brightness applications where a point source of light is needed. The PhlatLight RGB LED is said to be capable of producing over 3,000 white lumens.

"PhlatLight LEDs are being designed into a number of display and lighting applications," said John Langevin, VP of Sales and Marketing at Luminus. "National's LM3433 driver provides a more complete solution for our customers, enabling use at the intended high performance levels that the PhlatLight chipsets were designed for."

National's LM3433 is a constant on-time dc-dc buck (step-down) constant-current regulator. It outputs a negative constant current for lighting high-power, high-brightness LEDs. The negative voltage option allows the anode of the LED to be tied directly to the ground-referenced chassis for maximum heat sink efficacy. The short constant-on-time architecture allows the use of small external passive components and no output capacitor. Two current control modes modulate LED brightness. An analog current control input is provided so the LM3433 can be adjusted to compensate for LED manufacturing variations. The other current control is a logic-level dimming input for PWM control of LED brightness. The PWM functions by shorting out the LED with a parallel switch, allowing high PWM dimming frequencies up to 40 KHz. Additional features include thermal shutdown, VCC under-voltage lockout and logic-level shutdown mode. The LM3433 is offered in a 24-pin LLP® package.

Available now, the LM3433 is priced at $2.25 each in 1,000-unit quantities.

comments: 0