面向便携设备的白光LED驱动应用指南

　　Manufacturers of smart phones， cell phones， and PDAs are incorporating digital camera technology into their products so they can be used as cameras as well as for their intended use. Each of these devices uses a megapixel CCD camera that generally performs poorly in low-light conditions such as indoors， on cloudy days， or in the morning or evening. To provide a photoflash function for these low-light conditions， manufacturers are starting to turn to new high-power， white-light LEDs. These LEDs output a wide light spectrum and are compact and easy to control. They operate at much lower voltages than Xenon gas-discharge tubes， which require hundreds of volts to flash. Additionally， white-light LEDs can be left on continuously to provide lighting for digital movie photography. One challenge in using white-light LEDs is powering them with the wide input-voltage range that batteries present. A white-light LED can have a forward voltage ranging from 3.2 to 4.8 V. This falls in the middle of most battery input-voltage ranges， which means the converter needs to be able to step up or step down the input voltage to maintain the forward voltage of the LED.