For DC fan users, customers often for one or more of the following reasons, the fan speed can be controlled: 1, in order to reduce DC fan noise, in order to achieve user-specific cooling effect and noise requirements. 2. In order to increase the service life of DC fan, the rotating speed of DC fan is reduced to the minimum to prolong the service life of DC fan under the premise of satisfying the cooling effect of customer. 3. In order to automatically control the speed of DC fan according to the environment, in order to keep the target equipment working at safe operating temperature. Step by step cooling of the automated system in order to allow DC fans to operate at preset, varied speeds, etc. . DC Fan speed control method, the common method is to convert the control information into after the relevant channel input to the DC fan leads; 1. By the voltage signal-(V)2, by the current signal-(I)3, by the resistance change reaction temperature change (thermistor)-(t)4, by the resistance change of the manually adjustable passive resistor-(R)5, by the external PWM signal-(p)(pulse width modulation signal) Pulse Width modulation (PWM) signal is a very common signal produced by computer (or single-chip microcomputer) according to computer instructions 

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