Conductive EMI reduction in DC-DC converters by using the randomized PWM

In this paper, a comparative investigation on use of different random modulation schemes against the normal pulse width modulation (PWM) for the dc motor drive with step-down chopper (buck) and with half-bridge configuration is presented. For that purpose one experimental setup with DSP2 board has been developed. The board consists of the signal processor TMS320C32 which is suitable for verifying the different modulations strategies. The effectiveness of randomization on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes is evaluated by the power spectral density (PSD) estimations in the low-frequency range. Finally, one universal demo board with both power converters configuration (driven by the micro controller PICF16F876) has been used in EMI measurements to comply with the CISPR 25 (or EN 55025) regulative.