A multi-phase DC/DC converter is provided with: a plurality of converter units (11A, 11B,,, 11F) each connected in parallel with an input unit and an output unit and performing a power conversion; an output current detection circuit (5) for detecting an output current (Io); and a control unit (15) for, according to the detected output current (Io), determining the number of operating units (N) of the converter units (11A, 11B,,, 11F) and performing a switching control at a switching frequency (F) so that the phases of the determined number of operating units (N) of the converter units are different from each other. The product of the number of operating units (N) and the switching frequency (F) is outside the broadcast band range. This provides a multi-phase DC/DC converter and a multi-phase DC/DC converter system, in which noise caused by switching does not affect the broadcast band.
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