LEDs can be driven efficiently with a buck regulator circuit that uses a transistor to alternately conduct and interrupt current flowing from the input voltage to an inductor and diode, storing energy in the inductor during conduction. This topology can directly replace linear regulators and efficiently step down the input voltage to a lower level needed to power an LED. The control circuit drives the transistor to transfer the stored energy from the inductor through the diode to power the LED while maintaining a constant output voltage.

1. Driving LEDs (II) http://dev.emcelettronica.com/print/51768
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Driving LEDs (II)
By Emanuele
Created 09/04/2008 - 10:00
BLOG Diodes
by Franco Musiari [ DESIGN IN [1]]
Buck Regulators
This is the simplest topology - see Fig. 5 – and can directly replace the linear regulators
previously described. The control circuit drives a transistor alternately in conduction status
and interdiction status. During the conduction status the current flows from VIN to the diode
(green dotted line on Fig. 5) and the energy initially associated to delta between VIN and the
voltage fall on the LED, on the transistor and on RS is stored in the inductance. At the