Output Noise and Ripple

Ultimately, the power supply is only part of a larger system. Therefore, besides being concerned about the effect of noise and ripple on the converter itself, we need to worry about its effect on the rest of the system. The good news is that if the system were excessively noise sensitive, no one would have touched switchers with a ten-foot pole (or a lOdB zero) in the hrst place. They would have been using those low-noise, power-guzzling LDOs (linear regulators) instead  

Pickup Coil / Antenna unintentionally created (picks up noise) 

Output bypass cap too far from point of measurement (traces pick up noise too) 

Output Noise and Ripple, and Its Relation to Input Noise and Ripple (PSRR) 

Engineers are known to beef up the input capacitor for various reasons. At least some are hoping to reduce the output noise and ripple That actually does work in some cases, but the arguments are subtle and need to be qualified, depending on the type of converter and its application. Let us go through the reasoning. 

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Figure 3-1 Wrong Way to Measure Output Noise and Ripple...

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