What is ripple current?

Ripple current is a factor in all power supplies, even DC to AC power supplies, though the effect is most noticeable in AC to DC or DC to DC power supplies. Ripple current is simply the current that flows into and out of capacitors which, as nearly all power supplies are heavily dependent on capacitors, occurs often with power supplies. How this affects the output is that this change in current is directly related to a change in voltage. Thus, ripple current is a negative aspect of power supplies and is one measurement of how noisy a power supply can be. The larger the ripple current, the noisier the power supply. It should be noted that, perhaps ironically, ripple current is measured in volts (often millivolts) instead of amperes.

While ripple current is one way of gauging the quality of a power supply, it isn’t the only factor. Many applications are unaffected by small variations in voltage or, if there is a need for smoother voltage output, these variations can be removed with external circuitry. There are even power supplies that output the same voltage as input and only act to reduce ripple current and any other external noises.