Boost converters simplify drive circuitry for white LED backlighting

6 October 2004 Power Electronics / Power Management

ON Semiconductor has introduced fully-integrated white LED boost converters that drive up to five white LEDs in series to simplify and miniaturise colour LCD display illumination. Highly power-efficient backlighting - accomplished in a compact PCB footprint - is required for the colour LCD displays that are quickly becoming standard equipment in most new digital cellular handsets, PDAs and digital cameras. A series configured array of white LEDs is currently considered the most effective backlighting solution for the design of colour displays because this architecture achieves ideal current matching of the LEDs to provide uniform lighting.

ON Semiconductor's NCP5007 and NCP5006 can offer such a solution. The devices operate as a DC-DC boost converter that regulates the current through the LED string. Dimming is accomplished by applying a pulse width modulated signal (PWM) to change the average output current. In addition to being offered in a compact, low-profile SOT23-5 package, the NCP5007/6 incorporates built-in over-voltage protection that eliminates the need for an external zener diode. This works to simplify and miniaturise the circuit.

With an input voltage range of 2,7 V to 5,5 V, the devices are ideal for battery power applications that use 1-cell Li-Ion battery or ¾-cell NiMH batteries. In addition, the NCP5006 is available in an industry standard pinout which makes it easy to implement in existing platforms.

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