Label: Q: What does the DC on the machine mean? Answer: Direct Current (DC) refers to the current whose direction and time do not change periodically, but the magnitude of the current may not be fixed, resulting in a waveform. The circuit passing through is called a DC circuit, which is a closed conductive loop composed of a DC power supply and resistance. The direction of DC current and voltage is the same, and there are '+' and '-' poles. However, the voltage and current of the DC power also fluctuate. For example, after the diode is rectified before being filtered and stabilized, this is called pulsating DC, but the direction of the DC is always the same. From positive to negative. Battery power supply is a kind of direct current.