Dithering in circuits

Are you designing a board which requires agency certifications? Do you want to control any EMI/EMC concerns that are arising out of power supply section. One way to address your concerns is dithering of power supply. You might have taken proper concerns in layout but sometimes the power supply may be the source of noise in spite of extreme care taken in design. Dithering is nothing but a small electronic circuit to control the switching frequency of the power supply. The frequency spectrum of the oscillator can be spread to increase the band of frequency. Frequency spread meant distributing the total energy among the multiples of fundamental frequency. The dithering circuit is a simple op-amp circuit controlling the voltage into one of the frequency determining pin of the switching power supply. The voltage on this pin of switcher determines the frequency of operation of the switcher. Have you ever used a spectrum analyzer to probe a frequency generator in the circuit? If you try to probe the signal, you see a peak at the fundamental frequency of the switcher but if the signal is measured with dithering applied we can see the signal distributed over a band of frequencies. This technique can also be said as spread spectrum where the frequency is spread over a band.