"220V Cooling Fan" is the use of direct current operation, which is we all know, then what is it DC? It is understood that "DC" (Direct Current, called DC), also known as the "constant power", a constant current is DC, is the same size and direction of DC, in 1747, the experiment proposed the law of conservation of charge, and It defines the terms positive and negative charges. The constant current is the size (voltage level) and direction (positive and negative) does not over time (within a relatively range) changes, such as batteries. "220V Cooling Fan" refers to a direction pulsating direct current (positive and negative) unchanged, but the size change over time, for example: we 50Hz AC obtained after the diode rectifier is a typical pulsating direct current, half-wave rectification of 50Hz is obtained pulsating direct current, or if it is a full-wave bridge rectifier get is 100Hz ripple current, they only pass filter (inductance or capacitance) after it becomes smooth DC, of course, "220V Cooling Fan" in which there are still pulsating component (called ripple factor), depending on the size of the filtering effect of the filter circuit.