A switching device 30 and a related operating method are disclosed for generate a train of drive pulses under a basic pattern for a repetition cycle time T. The train of drive pulses has leading edges shifted from basic time periods T1 by shift amounts .PHI.0 to .PHI.02, respectively, which are different from each other, whereby switching frequencies, occurring based on the leading edges of the drive pulses, are spread. A spread frequency, which is a inverse number of the cycle time T of the basic pattern, is set to be higher than an audible frequency.