US Patent 7928712 Low noise fast dithering switching power supply

The present invention is a switching power supply that switches (dithers) between at least two switching frequencies without introducing a ripple signal at the dithering frequency, which is based on the time duration of a dithering cycle. In one embodiment of the present invention, an average current in an energy transfer element, such as an inductive element, during operation using one switching frequency is regulated to be approximately equal to the average current during operation using any other switching frequency. The average current may be regulated by controlling the durations of transition periods between operating using one switching frequency and operating using another switching frequency. By maintaining a constant average current while operating using different switching frequencies, dithering frequency ripple may be significantly reduced or eliminated.