this paper relates to the technical field of computer cooling fan , in particular to a driving circuit of a three-stage variable speed DC brushless cooling fan which can be controlled by a computer.

at present, the variable speed DC brushless cooling fan on the market is mainly used for cooling the computer system.it has no direct connection with the computer system circuit, and the computer system circuit cannot control the rotating speed of the fan.it is limited to connecting a thermistor in series at the power input end of the fan.the thermistor resistance power consumption is large, and the fan speed changes little with temperature, so the fan will lose some energy consumption in vain.

the purpose of this paper is to connect the fan with the computer system circuit.the speed of the fan can be controlled by the computer system circuit, and the speed can be adjusted with the change of temperature, and can be adjusted in three different speed sections, thus saving energy consumption.

this paper is realized through the following technical scheme:the drive circuit of the computer-controlled variable speed DC brushless fan is characterized in that it comprises four parts, namely a voltage dividing circuit, a comparison amplifying circuit, a winding pulse amplitude control circuit and a winding work monitoring circuit, and is connected with , the last three circuits all have DC amplifiers, among which:INPUT1 in the voltage dividing circuit inputs 12V power supply voltage, INPUT2 inputs computer system voltage signal, INPUT2 is connected with series resistors R1 and R2; In the comparison amplifier circuit, the collector of transistor Q1 is connected to nputi, the base electrode is connected to INPUT2, and the load resistance of the collector of transistor Q1 is a parallel connection of two groups of resistors R4 and R5; The collector of transistor Q2 is connected between R4 and R5 through load resistor R6, and the base electrode is connected between series resistors R1 and R2 of INPUT2. In winding pulse amplitude control ; Capacitors C1 and C2 are respectively connected in series with motor windings L1 and L2 to act as filtering capacitors to absorb sudden waves generated when motor windings L1 and L2 work; The base of the transistor Q2 is connected to the load resistor R6 of the transistor Q2 in the comparison amplifier circuit (2); The winding work monitoring circuit is connected to winding on the output of group L2. In order to test the working current of the motor winding, the base of the transistor Q4 is connected to the output of the motor winding L2 through the resistor R7.when the motor is working, the output of the transistor Q4 is a square wave signal, and the square wave signal increases with the increase of the rotating speed high, when the fan stops, transistor Q3 outputs a direct wave.

the voltage dividing circuit in this paper provides constant voltage and computer system voltage signals to the comparison amplifying circuit respectively.the comparison amplifying circuit provides different bias currents to the winding pulse amplitude control circuit under the control of the computer system voltage signal.the winding pulse amplitude control circuit provides working current to the motor , the winding work monitoring circuit monitors the working current of the winding pulse amplitude control circuit, so that the motor speed of the fan can be controlled by the computer system circuit. By selecting the resistance values of R4, R5 and R6 respectively, the fan speed can be adjusted in three different speed sections. Computer system electricity road can adjust the fan speed according to the temperature change, thus saving energy consumption.