This thesis summarises the studies carried out and the results achieved concerning the optimization of the Electromagnetic Interference (EMI) emissions on a DC-DC power converter by means of the spread spectrum technique. The power converter taken into account is the L6983, a synchronous step-down switching regulator produced by STMicroelectronics. In the first part of the work, the device was analysed in the laboratories of the "Politecnico di Torino" so as to describe the characteristics of the EMI emitted spectrum and to define a possible scope for improvement. Successively a 6-months internship was carried out at STMicroelectronics (Aosta headquarters) during which the architecture of the device was thoroughly studied together with some different clock dithering solutions in order to eventually implement in the L6983 the optimum one..