LED Drive Solutions and Power Supply Design ideas. Robust and efficient high-brightness LED drivers. Zetex have LED drivers for boost/buck they are cost effective too,
Shown below is a design from an Application Note of Zetex. Here ZXSC400 drives a Luxeon V Star LED. The input voltage ranges from 4.2V to 5.4 V with a maximum output current of 700mA at 5V input.
Voltage mode boost converter in the SOT23-6 package. Its low feedback voltage allows the current in a chain of LEDs to be set and accurately monitored with a single resistor giving minimal losses. Excellent load and line regulation.
1.8V to 8V supply range, regulation of ±1%, 80% efficiency, 4.5µA Quiescent drain.