Pwm: what is it and what is it for in fans

Something that surely few people already know what almost no one notices in terms of the characteristics of PC fans is in the PWM function, for which you must have important knowledge related to the technical part of computing. However, computer users are more used to this function than we think.

The tasks carried out by the PWM run in the background and without being noticed, although its advantages are visible on the PCs we use.

In recent years, hardware manufacturers have paid special attention to the possibility that the speed of the fans that cool various electronic devices, such as computers, can be controlled efficiently through the integrated circuits of the components. personal.

The evolution that the technology used by the electric fans that we find in today's electronic equipment is very important. Fans that have been used for many years, and which in turn have been modified to offer more and more advantages.

But this was not always the case, since until not many years ago, the possibility that a computer was silent and that it included a function to control the speed of the fans was not present in any model.

Several years ago, we did not find any form of active cooling on x86 computers, mainly because they did not generate excess heat inside the PC cases. But this began to change with the first 486 computers, which required more resources to perform more and more tasks.

From that time until today, computers began to consume more and more energy and also generate more heat, although they also began to obtain higher yields.

It is for all this that in addition to the evolution of the components, the cooling systems also underwent important changes and evolutions, mainly in terms of the way to control the speed of the fans, which is done through PWM.

Through a simple "volt mod", with which you could select 5, 7 or 12V from a classic Molex connector, you could control the speed of the fans several years ago.

Subsequently, resistors began to be used to decrease the speed of the fans, as well as the use of potentiometers and thermal resistances, thereby exercising wide-range manual speed control. The well-known rehobus.

But currently, if you are looking to control the speed of the fans and pumps, the most used and efficient option is PWM control or the use of drivers from manufacturers such as Corsair or NZXT to manage the speed of our fans via software or BIOS..

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Today, manufacturers launch their mid-range motherboards equipped with at least a 4-pin PWM header. For a bigger budget, high-end motherboards include four or more 4-pin connectors that control the speed of equipment's cooling systems.

Despite this evolution, there are still many people who do not know about this motherboard function that emerged in 2003, or do not take it into account when buying a computer. Even more surprising is that today we can still find fan manufacturers creating their components including outdated 3-pin connectors.

For this reason, we will explain what PWM control is, how it manages the speed of pumps and fans, and what advantages are obtained by knowing how to use this function, which is still ignored by most users.

How PWM Works

The operation of the PWM needs a circuit that has parts that fulfill different functions each. In this circuit, the comparator works as a link, and is made up of one output and two different inputs.

When making the configuration, keep in mind that one of the two inputs will take care of giving space to the modulator signal. On the other side, the second input has to be attached to a sawtooth type oscillator so that the function can be carried out properly.

The signal provided by the toothy oscillator is what sets the frequency output. Over the years, the PWM system has already proven that it works correctly, making it a widely used feature when it comes to managing the availability of energy resources.

Types of PC fans

Taking into account the number of cables with which a fan comes from the factory, it is possible to differentiate them according to three main types of connections.

If they come with just two ground wires, these fans have positive and negative connections. The second group of fans comes with three wires; two are responsible for powering the fan, while the third carries the tach signal, also known as the "Tach". By means of this third cable, a signal of an equal frequency can be transferred at the speed of the fan, which is measured in RPM (revolutions per minute). The last type of fans comes with four cables, which are what we know as “PWM fans”. One wire is grounded, the second is responsible for power, the third counts RPM, and the fourth transfers pulses to the fan.

PWM Control Uses

Although you might think that the term PWM (Pulse Width Modulation) or Pulse Width Modulation, in Spanish, is little used, the truth is that it is usually widely used in areas such as electrical engineering, and may be useful in various sectors, such as in telecommunications, servo motor devices, audio equipment, and many more.

Ultimately, the PWM performs the function of a switch, turning it on and off continuously, thereby adjusting the amount of power the pump motor or fan gets.

This motor is a fundamental part for a PWM system in charge of controlling the speed of pumps and fans, working at + 12V (full power) or 0V (zero power).

The speeds reached by the pumps and fans will be directly determined by the width of the PWM signal, or what is the same, by the time the motor remains on.

To give us an idea, a 10% duty cycle means that the PWM will send a few pulses of power in a certain period of time, causing the motor to run at a low speed. On the contrary, with a 100% duty cycle, a fan or pump is operated at maximum speed, that is, with a continuous engine start.

Liquid refrigeration

The energy consumption demanded by the pumps used in water cooling is considerably higher, which is why the energy is mostly connected to the Molex connector, while the other two cables of the PWM and the tachometer are connected to the motherboard header in order to manage the PWM as well as the speed.

In case there is no PWM signal in the fans, then the operation will be at its maximum power, while the liquid cooling pumps will have an average speed. In other words, if you want to run the pump at full power, you will have to connect it to a PWM signal that is set to 100% duty cycle.

Molex connection in D5 Pump (Corsair Hydro X Series), although it can also be purchased with a 4-pin PWM connection.

Premium fans include their own unique IC drivers within the motor core that create a slanted PWM signal instead of a flat square. These last signals tend to produce annoying squeaks at the moment when the fan speed is minimal.

This annoying noise is due to the fact that when the motor receives an abrupt increase in power, this causes the rotor to move, thus generating these clicks that sometimes annoy the user.

To avoid this, you must resort to using special integrated circuits, which will ensure that the engine ignition is smoother when receiving a boost.

Why is PWM so important?

It is normal for almost all fans in a computer to turn off when the voltage is set to about 5V or less. In these cases, the fans stop working and no longer rotate, which is why the fan manufacturer's stated speed range is often only achievable using PWM regulation.

In this way, through the PWM control, the fans can be made to work at very low speeds, around 300 to 600 RPM.

When these speeds are reached without the fans stopping, you get really quiet operation, plus with the PWM control they can be turned off if the user wants.

Another interesting feature about PWM control is that with a simple signal it is possible to control all the fans. Considering that the fans receive 12 volts continuously, special splitters can be used to send a PWM signal to all the pumps and fans in the equipment. In this way a harmony is achieved in the operation of all the fans and pumps.

Nowadays, the motherboard manufacturers give more and more relevance to the issue of PWM regulation, which is why there are very robust and detailed configurations on the market that make it easier to use this resource.

With the help of the PWM there will be no more annoying noises when the equipment components are fully operational, since they can work at low speeds as well as regulate the PWM duty cycle curve based on the temperature readings.

Advantages of PWM control

Using a regulator in the speed of pumps and fans can benefit us in several aspects:

A fan running at a slower speed produces fewer annoying noises. By running at a slow speed, the fan consumes less energy. Low fan speeds increase its life and performance.

But above all, the greatest advantage obtained with the PWM control is its high level of efficiency, its simple operation and the low cost of implementing it, taking into account that the fan will remain fully on or off.

There are several reasons why PWM control continues to be not only a highly popular system, but also a highly effective one.

It is a fact that motors as a whole, but DC motors in particular, act very quickly to the PWM control, allowing them, for example, to adjust their speed in a few seconds when they receive the PWM signal. Also, these signals that control the speed of the motors are very fast, mainly when little or no calculation is needed.

When PWN default speed is combined with motor responsiveness, high-quality efficiency is obtained from PWM controllers, especially in applications that are highly temperature sensitive and require temperature changes to occur instantly.

Disadvantages of PWM control

Among the negative points that can be found to the PWM control, it should be mentioned that the information contained in the tachometer is limited when receiving the PWM signal, since the power does not always reach the fan.

However, it is possible to retrieve this information from the tachometer by using a technique commonly called "pulse stretching", which is to turn on the fan for as long as necessary to collect the tachometer information. This can lead to an increase in noise generated by the fan.

Another disadvantage of low frequency PWM is related to the noise generated by the commutation. That is, when the fans are continuously on and off, there is a potential for noise. The same is true for the speed of this switching, which if it does not become fast, a blink may become noticeable.

Finally, both the price of this regulation and the problems of interference caused by radio frequency are also negative points.

Final words and conclusion about the PWM connection

If we focus on the aspects of reliability, acoustic noise and energy efficiency, there is no doubt that the best way to regulate fan speed is to use a PWM unit with a frequency greater than 20 kHz.

Just as it eliminates the requirement for noisy pulse stretching and annoying switching noises associated with low-frequency PWM units, it has a much wider control range than other PWM controls offer.

By means of the high frequency PWM control, it is possible that the fan works at minimum speeds, close to 10% of the maximum power, contrary to the minimum speed that a fan with linear control could reach, being able to operate in this case at 50% of maximum speed.

PWM control is highly beneficial in terms of power consumption, since the fans are continuously running or turned off.

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Lastly, thanks to the fact that a fan can operate at very low speed with PWM control, its useful life increases, as does the reliability of the system.