Thought this might be of some interest....talks about cell-phones transitioning to white LED's. However a new technology might elimanate the need for backlighting. Most of the rest of the article is on the voltage requirements in cell-phones.
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First, growing demand for color displays is forcing a move away from using green or amber LEDs for backlights and toward white LEDs,
Bell said. Because white LEDs have a much higher forward voltage, 4 V compared with 1.8 or 2 V for conventional LEDs, they need a
step-up converter where none was needed before.
Additionally, color LCDs run off a higher contrast-bias voltage, "up in the 9-V range, and once again requiring a boost converter," he
said.
A wild card in the cell-phone-display game is the emerging technology of organic electroluminescent (EL) displays, which produce
color, operate at a lower voltage than the 9 V for color LCDs, and preclude the need for a backlight, thus saving power.
"Everyone is waiting to see if organic EL displays take off," said Bill Edmiston, semiconductor product manager at Toko America Inc.,
Mt. Prospect, Ill. If so, cell-phone power requirements will change once again.
(Where conventional monochrome EL displays are used as display or keypad back- lights in cellular phones and PDAs, they command
their own type of high-voltage AC-driver chips, a specialty of companies such as IMP Inc., San Jose.) |
