There are a lot of signal lines "220V AC Cooling Fan" device above, below we introduced by some of the output signal of the DC cooling fan. Fan cooling fan equipment each size can match FG or RD signal lines. Cooling fan has two lines, three lines, four lines. Two lines just positive and negative, in addition to the positive and negative poles than three additional lines for signal, and the signal line, there are two: one is the FG, which is the speed signal is a square wave signal, usually the signal frequency quadrupole fan * the actual speed of 30 = fan, there will be slow to say the actual speed. Another is "220V AC Cooling Fan" RD signal, its function is to run the fan output low, the fan does not turn the output high, CPU by detecting the signal can know whether the fan running. Four-wire "220V AC Cooling Fan", in addition to the positive and negative and FG, another usually PWM lines, from line changes the duty cycle of the PWM signal input to adjust the fan speed, speed and duty cycle variation is basically a linear generally at the high end did not change significantly. Change curve and the internal circuit design of the cooling fan, you can achieve different adjustment range.