3V battery powered white LED driver

The following circuit will drive LEDs of any color, including white LEDs, using a DC power supply ranging from 2V to 3.3V. White and blue LEDs typically require more than 3V, so the circuit uses a charge pump scheme to provide a constant LED light intensity from a voltage below 3V. The LEDs are driven with fast pulses of a 3mA peak current, which remains fairly constant even as the battery voltage changes. This circuit is designed only for low LED current applications. A common CR2032 lithium coin cell battery should power the lamp for two days. A pair of 2.5Ah AA NiMH batteries should power the circuit for nearly a month.