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A comparative investigation on the use of random modulation schemes for dc/dc converters is presented. The modulation schemes under consideration include randomized pulse position modulation, randomized pulsewidth modulation (PWM), and randomized carrier-frequency modulation with fixed and variable duty cycle. The paper emphasizes the suitability and applicability of each scheme in dc/dc converters. Issues addressed include the effectiveness of randomness level on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes, and the low-frequency power spectral density (PSD) of each scheme. The validity of the analyses is confirmed experimentally by using a dc/dc buck converter operating in continuous conduction mode. The PSD of the output under each scheme will be presented and compared.