This is the simplest topology 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 increasing of the stored energy in the magnetic circuit, the resistance decreases to the passage of the current, current that grows until the controller, that measures it on RS, does not drive the transistor to the interdiction status.