with the rapid development of computer technology, computer systems usually need to carry out a large number of operations, and the amount of heat generated during busy tasks also gradually increases.heat dissipation problems cannot be solved by heat dissipation holes and fins alone.for active heat dissipation equipment, air cooling technology with high cost performance has always been the most commonly used cooling method for computer systems, however cooling fan although it is economical and practical, it also has many defects:with the increase of rotating speed, the noise generated by the cooling fan in high-speed operation also gradually increases:long-term high-speed operation will not only shorten the cooling the service life of the fan, and the cooling fan itself also generates a lot of heat.

if the cooling fan can run at high speed when the system is busy and reduce the rotating speed or even stop when the system is running smoothly, it can be used in the most reasonable way, not only prolonging the service life of the cooling fan, but also reducing unnecessary heat generation. The existing intelligence SmartFan technology is developed to realize the reasonable use of the cooling fan.it uses Intel's Pulse Width Modulation, PWM) specification to control the PWM duty cycle to control the speed of the cooling fan. Since the PWM change is based on the temperature data read by the diode in the central processing unit, and its accuracy exceeds that of the thermistor, the rotation speed of the radiating fan is adjusted according to the duty cycle of the PWM pulse width, and its control precision is degree is also very high.

through intelligent cooling fan technology, users can independently set the temperature limits of CPU and motherboard in Basic Input Output System,BI0S).when the cooling fan judges that the temperature exceeds the set limits through PWM pulses, it will automatically operate , and the rotational speed can be adjusted according to the amount of heat generated:on the contrary, when the temperature does not exceed the set limit, the cooling fan will rest properly.

however, only the 4-pin heat dissipation fan in the existing heat dissipation fan can realize the function of an intelligent heat dissipation fan through PWM, and the 3-pin heat dissipation fan cannot receive PWM signals because there is no corresponding pin, so the 3-pin heat dissipation fan still needs to change its working voltage by small to control the speed.

at present, there are various mainboards supporting intelligent cooling fans in the market, but they all have a common defect, and only one of 3-pin or 4-pin cooling fans can be supported. In this way, for customers, the choice of cooling fan will bring inconvenience to them, and the same applies to for manufacturers, due to the limitations of the motherboard on the type of cooling fan, different requirements are also put forward for the selection of cooling fan connectors, increasing the difficulty of component procurement. If the control circuits required by the 3-pin and 4-pin cooling fans can be integrated, the motherboard can automatically distinguish the type of cooling fan and control its rotating speed, then such problems will no longer occur.

summary of the invention:

in view of the above, it is necessary to provide a computer cooling fan control circuit, which can selectively control the rotation speed of different types of cooling fans.

it is also necessary to provide-a 3-pin cooling fan speed control circuit.

the inverting input end of the operational amplifier, the non-inverting input end of the operational amplifier is grounded through a first voltage dividing resistor, the output end of the operational amplifier is connected with the first end of the current controller through a first current limiting resistor, the second end of the current controller is connected with a first power supply, and the first three terminals are connected to the power supply pin of a heat dissipation fan connector and connected to the inverting input end of the operational amplifier through a second voltage dividing resistor, the detection pin of the heat dissipation fan connector is connected to the rotation speed counter, and the control pin of the heat dissipation fan connector is connected to the operational amplifier through a second current limiting resistor receives a second pulse width modulation signal sent by the input/output control chip, and the computer cooling fan control circuit detects the cooling fan rotation speed measured by the rotation speed counter when the duty ratio of the second pulse width modulation signal is changed judging the type of the radiating fan according to the change situation, and sending the first or second pulse width modulation signal according to the type of the radiating fan to adjust the rotating speed of the radiating fan.

the phase input end is grounded through the integrating capacitor, the non-phase input end of the operational amplifier is grounded through a resistor, the output end of the operational amplifier is connected to the first end of the current controller through a resistor, the first end of the current controller is connected to a power supply, and the third end of the current controller is connected to a power supply through an electric the resistor is connected with the non-inverting input end of the operational amplifier and the second pin of the heat dissipation fan connector, the current flowing through the first end of the current controller is proportional to the current flowing through the third end of the current controller, and the first pin of the heat dissipation fan connector is grounded 。

the above computer cooling fan control circuit can distinguish the type of cooling fan by changing the I of the pulse width modulation signal for circulation and comparing the measured cooling fan rotation speed, and automatically select an appropriate circuit to control the cooling fan rotation speed according to the discrimination result, which is quite consistent with reasonable and convenient.