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There are a lot of white LED driver circuits floating around. A
popular circuit called the “Joule Thief” can drive one white LED from a single
1.2v or 1.5v battery cell. Most of these circuits use one or two transistors
to form a voltage boost circuit. Yes, they those circuit do drive a LED but
they are not very efficient and they don’t do a good job of controlling the
current to the LED. The circuit below uses a tiny LT1932 IC made by Linear
Technology. This IC can be configured for a wide variety of LED driver
needs. I have shown one simple application. The circuit takes power
from one 1.2v NiMH rechargeable battery or a 1.5v disposable battery and drives a
single white LED with 15ma of current. With an efficiency of about 70%, the
circuit should run for about 40 hours, if a quality 2500ma-hour battery is used.
Click on Drawing Below to view PDF version of Schematic
