Driver drives LED efficiency

STMicroelectronics has introduced a new white LED driver with specific features for small LCD module backlight and high efficiency white LED power supply for portable applications.

STMicroelectronics has introduced a special part to drive the white LEDs that are becoming popular for colour LCD backlighting or portable devices.

Colour LCDs demand a pure white backlight so their colours are properly displayed.

White LEDs are becoming the preferred technology for this but need a typical forward voltage of between 3 and 4V DC.

The latest lithium-ion batteries have minimum operating voltages down to 2.8V DC.

As the brightness of an LED is proportional to its forward current, dedicated current-source power supplies are needed to drive white LEDs from the batteries used in portable applications.

The STLD20D is an inductive boost convertor designed to drive a white LED with high efficiency over a wide range of battery voltages.

It can drive up to four LEDs in series from a 2.8V DC battery voltage and offers dynamic supply voltage rejection to prevent backlight flickering.

Conversion efficiency is more than 80%.

The part includes an LED disconnect switch to reduce current leakage in stand by mode, soft start functions and a shut-down mode with dimming control.

The STLD20D offers a low standby current of less than 1mA, and includes overvoltage and overtemperature protection.

The part has a pulsewidth modulation input, so that a white LED can be dimmed without reducing its biasing voltage, which could affect the colour of its output.

This allows a pure white colour to be kept over the entire dimming range.

Peak inductor current is adjustable on versions of the STLD20D packaged in an SOT-23.

The part is also available in a 3 x 3mm QFN.

Pricing is US $0.45 in quantities of 100,000 pieces.

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