Power Management For Portable Equipment Lighting

Jan. 13, 2005

What is behind the move to white LEDs in portable equipment?

The trend for color displays in handhelds has produced a parallel move to white LEDs for LCD backlighting. White LEDs provide the desired appearance for backlighting color LCDs. They're also more rugged and efficient, simpler to drive, and smaller, thinner, and far less noisy than the cold-cathode florescent tubes previously used for backlighting.

Why use driver ICs for white LEDs?

The simplest drive configuration for an LED is a voltage source and current-limiting resistor. However, a driver IC provides better overall performance. It can control white LEDs with a constant-current source that regulates their current regardless of power-supply voltage variations or variations in LED forward voltage drops. Also, the driver allows you to boost the voltage applied to the LEDs because the battery voltage can fall below the value required to turn on the LED.

What are the requirements for a white LED driver IC?

Many portable systems use a single lithium-ion (Li-ion) or multiple nickel-metal-hydride (NiMH) batteries to drive the white LEDs used for backlighting LCDs. The driver must provide the proper forward voltage for the white LEDs, which typically range from 3.3 to 4.0 V.

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About the Author

Sam Davis 2

Sam Davis was the editor-in-chief of Power Electronics Technology magazine and website that is now part of Electronic Design. He has 18 years experience in electronic engineering design and management, six years in public relations and 25 years as a trade press editor. He holds a BSEE from Case-Western Reserve University, and did graduate work at the same school and UCLA. Sam was the editor for PCIM, the predecessor to Power Electronics Technology, from 1984 to 2004. His engineering experience includes circuit and system design for Litton Systems, Bunker-Ramo, Rocketdyne, and Clevite Corporation. Design tasks included analog circuits, display systems, power supplies, underwater ordnance systems, and test systems. He also served as a program manager for a Litton Systems Navy program.

Sam is the author of Computer Data Displays, a book published by Prentice-Hall in the U.S. and Japan in 1969. He also authored the book Managing Electric Vehicle Power. He is also a recipient of the Jesse Neal Award for trade press editorial excellence, and has one patent for naval ship construction that simplifies electronic system integration.

You can also check out additional articles on his other author page.