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Technical Terms

Ripple and noise refer to the unwanted AC components superimposed on a DC power supply's output. This is often specified as PARD (Periodic and Random Deviation). Total output noise is a combination of periodic ripple and random, high-frequency noise.

Switching power supplies generate high-frequency noise due to the rapid switching action of transistors and rectifiers. The figure below illustrates the relationship between ripple, noise, and total ripple noise.

In contrast, series regulators (linear power supplies) lack high-frequency switching components and therefore exhibit significantly lower noise. Their output noise is primarily composed of ripple at the commercial line frequency and its harmonics.

Relationship between ripple and noise components

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