Rectifier output current and direct current, there is no essential difference, are all direct current. The difference is that the current output of the rectifier is a pulsating direct current, rather than the pure direct current output of the battery. A common rectifier circuit can be seen that the current output of the rectifier is composed of a sine wave 1\/2 waveform, which is called half-wave rectification. Or the other half of the waveform of the sine wave is collected in reverse by another rectifier diode, and then the full wave rectification current is gathered together. Whether it is half wave rectification or full wave rectification, the current is composed of half waveforms of one sine wave. The characteristics of each 1\/2 waveform are composed of 0 degrees to 180 degrees, and its current characteristics are changed from small to large (0-90 degrees), and then from large to small (90-180). That is, the current between the two half waves changes from large to small, and then from small to large. This change is called pulsation. This pulsation is smoothed by the charge-discharge characteristics of electrolytic capacitors. Therefore, the higher the frequency of the rectifier power supply, the smaller the gap of this pulsation will be, and the other way around. The smoothing effect provided by the capacitor is also that the larger the capacitance, the smaller the current change in its pulsation sag, and the reverse. Pure battery direct current does not have this phenomenon. Direct current is fundamentally different from alternating current. Direct current refers to its current direction is a single current direction, and the current direction of alternating current is bidirectional, and from 0 to the maximum, and then from the maximum to 0 between continuous change, in sine 360 degrees, represented by a straight line, can be restored to positive 180 degrees and negative 180 changes back and forth.