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A pulsating direct current contains components of both Direct Current (DC) and Alternating Current (AC) that changes in value over short periods of time.
A pulsating direct current may change in value, i.e., be always present but at different levels, or it may be interrupted completely. The changes may be irregular or at regular intervals (at a specific frequency), but the current never changes direction.
Pulsating currents are commonly the consequence of using diode rectifiers, or DC sources of lower amplitude connected in series with AC sources. It can be smoother, if a large value capacitor is used in parallel with the rectified source.
Pulsating direct current is used on PWM controllers.
Difference from AC
Pulsating direct current has an average value equal to a constant (DC) along with a time-dependent pulsating component added to it, while the average value of alternating current is zero in steady state (or a constant if it has a DC offset, value of which will then be equal to that offset). Devices and circuits may respond differently to pulsating DC than they would to non-pulsating DC, such as a battery or regulated power supply and should be evaluated.