Inductive-Based Switching Regulator Circuits Provide High-Efficiency White-LED Drives

Since the conception of cellular phones, PDAs, and handheld computers, there has been a continuing push for more useful and dynamic displays.  One of the more drastic changes in miniature display technology has emerged due to the availability of Internet content, pictures, and videos on ever shrinking personal devices.  The promise of more content and functionality has caused a migration towards higher resolution color displays.  This presents some added design issues, however, as a color LCD display requires white backlighting as opposed to the more standard green.  The current options are using a Cold Cathode Fluorescent Lamp (CCFL), an electroluminescent backlight,  or newer white-LEDs.  White-LEDs are quickly becoming the light of choice because of their falling costs, longer life, and smaller size.  The problem this presents is that the white-LED has a high voltage drop (3.1V to 4.0V depending on manufacturer) as compared to the green-LED with a voltage drop of  1.8V to 2.7V.  Whereas the green-LED can be powered directly from the commonly used Li-Ion battery with a linear regulator and a ballast resistor, the white-LED used for backlight or frontlight purposes will require the battery voltage be boosted.