1. Field of the Invention
This invention relates to a fan controlling system and method, and more particularly, to a fan controlling system and method for linearly adjusting a rotation speed of a fan.
2. Description of Related Art
With the rapid development of computer technologies, computers are becoming one of the most important electronic devices in daily lives. Since modern computers have better efficiency and can manage more complicated tasks, a central processing unit (CPU) in a computer has to be able to operate in a high operating speed. However, the CPU, if operating in the high operating speed, generates too much heat. The heat crashes the computer occasionally, or even brings nonrecoverable damages on hardware components in the computer permanently. Therefore, heat dissipating systems are becoming one of the most popular research fields in the art.
One of the most common heat dissipating systems is a combination of a fan and a plurality of heat dissipating plates. Such the combination has a simple structure, and has a variety of advantages, such as low cost, highly reliable performance, and adopting mature technologies. In order to dissipate the heat efficiently, the fan has to rotate at a high rotation speed occasionally. However, the fan, when rotating at too high a rotation speed, generates a loud noise. Moreover, the fan, if rotating at the high rotation speed all the time, is easily to have a breakdown.
A first fan controlling system of the prior art is brought to the market to solve the above problems. The first fan controlling system comprises a temperature sensor, and is applicable to an electronic device (i.e. a computer host or a desktop computer) having a fan capable of rotating at two rotation speeds, i.e. a low rotation speed and a high rotation speed. Please refer to FIG. 1, which shows a first relation between temperature and time of the first fan controlling system. As shown in FIG. 1, a first temperature curve 10 represents a temperature of the electronic device. Heat generated by the CPU changes the temperature. When the temperature exceeds a temperature threshold Ct, the fan is controlled to rotate at the high rotation speed, or the fan is controller to rotate at the low rotation speed, as shown by a rotation speed curve 12 in FIG. 1. One drawback of the first fan controlling system is that the fan has to change to rotate from high rotation speed to low rotation speed and vice versa frequently if the temperature fluctuates around the temperature threshold all the time. Such an scenario shortens the lifespan of the fan.
Please refer to FIG. 2, which shows a second relation between temperature and time of a second fan controlling system according to the prior art. In addition to the temperature threshold Ct, another temperature threshold Ct1, which differs form the temperature threshold Ct by a small temperature difference Δt, is added to the second relation. When the temperature exceeds the temperature threshold Ct (an upper bound), the fan is controlled to rotate at the high rotation speed. When the temperature is still lower than the temperature threshold Ct1 (a lower bound), the fan is controlled to rotate at the low rotation speed. When the temperature is within the temperature thresholds Ct and Ct1, the rotation speed of the fan is not changed, so as to stabilize the operation of the fan. However, the second fan controlling system still suffers the drawback of the first fan controlling system. For instance, the fan still has to change to rotate from high rotation speed to low rotation speed and vice versa frequently if the temperature fluctuates around the temperature thresholds Ct and Ct1 all the time (i.e. a second temperature curve 20 fluctuates around the temperature threshold Ct1, the fan has a rotation speed 220 changing abruptly). Such a scenario still shortens the lifespan of the fan.
Therefore, it is becoming one of the urgent errands in the art to present a fan controlling system and method to overcome the drawbacks of the prior art. Such the fan controlling system and method controls the fan to rotate without the influence of temperature fluctuation and reduces a noise made by the operating fan, and prolongs the lifespan of the fan.