A PC fan is one of the most important devices in the machine. It has the ability to influence how fast and effectively the whole system unit can work. Furthermore, the simple comfort brought by a silent fan can really enhance the efforts of a person who is working on a PC. Considering the importance of efficiency of a fan, it cannot be further emphasized that its functional aspects must be put into consideration. One such aspect is its speed. The speed of a PC fan determines the rate of cooling of other devices inside the PC so that it can either keep them efficient by cooling them at the required rates or let them overheat and damage the whole system. This article presents case studies for PC fan speed control. There are two main fan control technologies; the PWM and PI/PID.

PWM Control

The PWM control system is the standard of all computer fan control systems. Before delving into details, let us define it first. PWM is an acronym for pulse width modulation. It gives a fan control abilities that allow adjusting the rotation speed without having to adjust the input voltage that is fed to the fan.

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There are three types of PWM fan control systems. These are the two wire type, the three wire type and the four wire type. The two wire type allows the fan full speed rotation immediately the computer goes on. This is the oldest type in the market. Due to its inability for control, it is rarely used and it is about to be rendered obsolete.

The three wire type uses technology called ‘tacho’. This is the ability to sense the speed of the fan. This means that it can detect the speed at which the fan is running at any given time. The challenge with this type is that it does not allow for feedback systems. The three wire is one of the most common among computers in the modern world. However, it is not the latest in terms of PC fan technology.

The four wire type is the latest in the market. It also uses ‘tacho’ technology and in addition to that, it has the capacity to sense the speed simultaneously and this enables feedback system.

The PWM fan control system has a number of ways in which it operates. First, there are those that have no external control. They rely solely on the system unit. This means that the moment the computer is switched on, the fan starts running at a predetermined speed. When the user switches off the computer, the fan also stops.

The second control operation uses a thermostart. In such a fan control system, there is ability to set the upper and lower limits of the fan. Fan speed is usually measured in revolutions per minute (rpm). The number of revolutions in one minute is the one that determines what value is set as the maximum and what value is set as the minimum. The bracket is dependent on the amount of cooling and the choice of whether to switch to maximum or minimum is dependent on the amount of processes being handled by the computer (and thus heat emitted).

Other methods include the linear voltage method where a linear voltage regulator is used to vary the amount of voltage that is applied on the motor so that the motor can in turn vary the rate of rotation of the fan and the diode technique which also varies voltage and thus the rpm.

The 4 pin Molex connector KK family is the most common PWM connector. It has the capabilities of the traditional 3 pin Molex connector except for the fact that it has an additional pin that is dedicated to PWM. This additional pin is the one that is responsible for varying speed control.

PI/PID Control

PID is an acronym for proportional, Integral and Derivative. All these three components that form the whole PID function create output that is dependent on the measured error of the rpm of a PC fan. In order to understand how the whole system works, it is important to understand how each individual component of the PID Control system contributes to the role.

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Proportional: the output of proportional component is a product of gain and error. This means that an increase in either gain or error or both leads to a higher value of the proportional component and thus a higher value of its output.

Integral: this is where all measured errors of the fan control system are stored. When the integral component has collected very few errors, is operation is at a low but when it has collected many errors it is optimal. This means that its role is to collect as many errors as possible.

Up to this point, the two components of the control system (P and I) can work effectively as they are. This means that even without the derivative function, the other two can still control the fan effectively. This is why it is also called the PI control.

Derivative: it focuses on the rate of change of error. In function, its main role is to countercheck overshooting of the other two components; proportional and integral functions. As a result, a stronger PI dampens the D and a stronger D dampens PI.

The whole control system allows fine tuning of the fan loop. This is because its use is controlling variables. In the context of PC fan, the PID loop is responsible for automatically detecting whether temperature (the variable) is at its optimal point. If or when it is not, then the control system will consider the current value of error over time interval and the rate at which the error is changing. It will then determine how much of the necessary correction should be applied so that the fan can operate at its optimum level.

For those PCs that run on PID, users are able to tell when the control function is automatically activated. The fan usually runs very fast and within a short period of time one can almost tell that the system has cooled down.