Patent ID: 7425781

Claim:
An electric power switching apparatus comprising switching circuit means controllable for performing successive switching operations to repetitively interrupt a flow of DC current, and control circuit means for generating a switching control signal for controlling said switching operations, wherein independent of a selected AM frequency, said control circuit means selects successive ones of a predetermined plurality of pulse period patterns having respectively different values of pulse period to generate said switching control signal as a series of said pulse period patterns, with successive pulse period patterns of said series having respectively different values of pulse period, and disperses a power spectrum of high-frequency harmonics of switching frequencies of said switching operations along the frequency axis within a radio broadcasting waveband; and said pulse period patterns having respectively different values of pulse period are predetermined such that none of a plurality of switching frequencies that are respective inverse values of pulse periods of said pulse period patterns shares a common multiple with any frequency that is within a predetermined AM (amplitude modulation) radio broadcasting waveband.