Although white LED drivers have been available for several years, demand has soared in the past year as new mobile phones and PDAs are produced with color rather than monochrome displays.

No market surveys exist on the number of white LEDs being shipped, but suppliers say that their use has risen sharply.

"Three to four years ago, there were perhaps 200 million to 300 million mobile phones, and they used monochrome displays," said Tony Armstrong, product-marketing manager of the power business unit at Linear Technology Corp. (Milpitas, Calif.). This year, Armstrong estimates that of the more than 400 million handsets that will ship, at least 60 percent to 70 percent are equipped with color LCDs, as are about 10 million PDAs.

"When you add these up, it doesn't take long to see there are hundreds of millions of sockets for white LED drivers," he said.

The automotive market is also demanding more white LED drivers, Armstrong said. "There will be continued proliferation of white LEDs into nonportable applications, such as traffic lights, brake lights and automotive instrument panels."

IC drivers are needed because the white LEDs, which have a typical voltage drop of 3.5 to 4 V, can't be driven directly from a low-voltage battery when connected in series. "You need an IC to transfer and boost the battery voltage," said Patrick Heyer, product-marketing manager of portable power-management products at Texas Instruments Inc. (Dallas).

While many suppliers of white LED drivers have extensive offerings of other power-management devices, some chip makers with strengths in other areas are nevertheless developing products for this market. One is Catalyst Semiconductor Inc., which expects to leverage its E2PROM process technology for white LEDs.

"We'll offer the cost and efficiency benefits of high-volume E2PROM manufacturing," said David Gillooly, director of marketing and applications, who expects Catalyst's white LEDs to be cost-competitive with rivals' parts.

The Sunnyvale, Calif., company's initial offering is the CAT32, a switched-mode, constant-current boost regulator operating at a 1.2-MHz fixed frequency. The chip boosts a low-voltage battery and automatically regulates driven current for up to four white LEDs operating in series.

Catalyst faces stiff competition from several chip makers that have provided white LED drivers for several years and are expanding their portfolios.

Linear Technology has introduced a white LED driver with an on-chip Schottky diode. "A lot of suppliers integrate the MOSFET on the driver but not the diode," Armstrong said. "You only need two external capacitors, a resistor and an inductor to complete the driver circuit."

For TI, the key focus is to improve the driver's circuit design in order to increase efficiency and extend the LED display's battery life. "White LED drivers are often in the display module rather than on the motherboard, complicating integration," Heyer said. "We're trying to reduce the quiescent [off-state] current of the drivers."

By: DocMemory
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