2015/8/7 下午 05:02:57        Administrator        General   126 Comments
Fans found in motherboards primarily serve the purpose of dissipating heat generated by the board and are set to run at a defined RPM under normal circumstances. But in order to remove as much heat as possible, these fans will typically be tuned to operate under their high-speed settings. This move, while beneficial from a heat removal standpoint, also speeds up the fan, leading to an increase in the amount of noise generated. Moreover, the fact that the amount of heat to be removed is dependent on applications also makes high RPMs not necessarily be an integral part of a computer’s normal operation.  
In the midst of seeking a balance between cooling and noise generated doing so, Smart Fan emerges.
What is Smart Fan? It is a function that enables the RPM of a fan be automatically adjusted: When the temperature rises, the fan runs faster; if temperature drops, it slows down. In other words, a fan’s RPM is now dependent on the temperature that Smart Fan detects. Therefore, whenever the fan is seen moving at an inconsistent RPM, more than mechanical failure, it is Smart Fan doing its job, actively controlling RPM based on the current temperature.
Smart Fan is most applicable in situations where users need not subject their computers to heavy loading in a low-noise environment. It is also advantageous for boards used in a low-temperature setting, as the lowered RPM helped preserve heat in the board for components more susceptible to the cold.
Smart Fans can be typically configured under the BIOS options. Users may configure their temperature levels according to their requirements and the duty cycle in which the RPM is controlled, or place a direct RPM value. Image (a) shows the temperature and Duty cycles corresponding to the Smart Fan settings. Image (b) shows an example where 50% of the PWM is outputted to the fan when the CPU temperature reaches 30°C; 50 – 60% at 30 – 40°C; 85% at 60°C and above.

                                                                               Image (a)

                                                                                  Image (b)

Fans commonly controlled using PWM are 4-pin fans, which sets itself apart from its 3-pin counterpart with an additional Fan Control input (as shown in image (c)). This signal enables RPMs to be controlled with PWM. On the other hand, as 3-pin fans lack the PWM option, its speed will have to be controlled by adjusting the fan power voltage levels. In terms of board designs, 4-pin fans, for their ability to use PWM as a mean to control RPM, can be controlled as long as PWM is supplied by the board; for 3-pin fans, boards will have to be designed in a way that PWM can be harnessed for adjusting the fan power voltage levels.
A good 3-pin fan design will be one that is capable of deriving different RPMs from different PWMs. When plotting RPMs against PWMs (image (d)), a gradual straight line will be shown when is board is well-designed, depicting different RPMs for different temperatures, while a less desirable design only controls the fan for a very narrow range of temperatures, severely limiting its “smart” potential.
For connectors, 3-pin fan connectors can be used for 3-pin and 4-pin fans, likewise for 4-pin connectors, though the latter case may lead to the inability for RPM control when applied on a 3-pin fan caused by design differences. Therefore, it is advised to use 4-pin fans when Smart Fans are to be achieved on a board with 4-pin fan connectors. 
With Smart Fans, fans are no longer bounded by a fixed RPM. So now, if you fear your system hanging from overheating, but noises from fans are getting too loud for comfort, give Smart Fans a try; let it automatically take charge of your fan speed based on temperatures.
                                                                             Image (c)


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