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I use Supertext chips
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), with excellent results, but there are similar chips readily available from National, AD, Maxim, TI, ON, etc. You can also easily find 1 and 2 transistor circuits for this purpose. The basic principle is to charge an inductor to a reference current with the LED in series, turn off the transistor, steer the inductor current through the LED, and repeat. There are other, similar topologies, including some that switch capacitors from series to parallel connection to provide higher or lower drive voltages for better efficiency. Paul Mathews