HOW TO TEST OUTPUT RIPPLE AND NOISE OF POWER SUPPLIESAPPLICATION NOTE HOW TO TEST OUTPUT RIPPLE AND NOISE OF POWER SUPPLIES The switching power supplies (either step-down regulators, or isolated DC-DC converters, or OFFLINE power supplies) have the fundamental advantage of high efficiency i.e. low power dissipation when compared to linear voltage regulation. However the switching technique, that is beneficial to raise the efficiency, has an associated weakness i.e. the output voltage has always an AC content. The typical output ripple and noise of a switching power supply is as shown in fig. 1. Figure 1. Output ripple and noise of a switching power supply Four AC components can be identified: low frequency ripple at 2f being f the AC mains frequency high frequency ripple due to Pulse Width Modulation (PWM) to obtain the required line an……