Pwm fan how does it work

A 4-pin PWM fan is driven by pulses with varying duty cycles. This brings us to the next question. Why is there a need for a 4-pin PWM connection when a 3-pin header will do? This feedback is useful for the motherboard to have, as it tells the motherboard if the fan is running at the required speed. It would be dangerous to have a malfunctioning fan with the motherboard temperature rising unnoticed, as overheating can damage internal components.

Built-in PWM modules spare you the hassle of writing code to emulate a software PWM, which can be tedious and challenging. Most 4-pin PWM fans require a signal with 25 kHz frequency, which should be within the capacity of most low-end microcontrollers. Inspecting, debugging, reworking, and assembling PCBs has never been simpler or more accurate. Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation.

A 3-wire fan can be controlled using the same kind of drive as for 2-wire fans—variable dc or low-frequency PWM. The difference between 2-wire fans and 3-wire fans is the availability of feedback from the fan for closed-loop speed control. The tach signal indicates whether the fan is running and its rate of speed. It is always valid, since power is continuously applied to the fan.

With low- frequency PWM, however, the tach signal is valid only when power is applied to the fan—that is, during the on phase of the pulse. Because the tach output is typically from an open drain, it will float high when the PWM drive is off , as shown in Figure 1. In order to be sure of a correct fan speed reading under PWM control, it is necessary to periodically switch the fan on long enough to get a complete tach cycle.

In addition to the power, ground, and tach signal, 4-wire fans have a PWM input, which is used to control the speed of the fan. Instead of switching the power to the entire fan on and off , only the power to the drive coils is switched, making the tach information available continuously.

Switching the coils on and off generates some commutation noise. Figure 2 shows the differences between 3-wire and 4-wire fan circuits. The main advantages of this are guaranteed fail-safe cooling and a very simple external circuit.

However, because the fan is always switched on, its lifetime is reduced and it uses a constant amount of power—even when cooling is not needed. Also, its incessant noise is likely to be annoying. This method is also very easy to implement. The fan is switched on only when cooling is needed, and it is switched off for the remainder of the time. The user needs to set the conditions under which cooling is needed—typically when the temperature exceeds a preset threshold. It has a comparator that produces a THERM output—one that is normally high but switches low when the temperature exceeds a programmable threshold.

Figure 3 is an example of a circuit using the ADM When a fan is switched on , it immediately spins up to its full speed in an audible and annoying manner. Because humans soon become somewhat accustomed to the sound of the fan, its switching off is also very noticeable. It can be compared to the refrigerator in your kitchen. Linear control: At the next level of fan control, linear control , the voltage applied to the fan is variable. For lower speed less cooling and quieter operation the voltage is decreased, and for higher speed it is increased.

The relationship has limitations. From the outside on the other hand you will be hard-pressed to find a difference — with the main exception of the connector: Regular fans have three pins, the PWM colleagues feature one more for the fan control. Which of course means that the motherboard, where these pins are connected to, must support them. Which can only cause problems on older models as PWM support has been standard in modern systems for quite some time now.

Cookies on bequiet. Accept only technical necessary cookies Information about the use of cookies. Accept all cookies. Thats a very good Read!!!! Voltage regulation is very limited since most fans just shut down if the voltage falls under 7 or 5V, depends on the fan model.

Having the speed regulated with PWM, it means that it is always getting 12V of power, but in little packets. This way the fan can reach slower speeds than if it was regulated by voltage. On top of that, you should know that the fans […]. Read more. Join the EKWB forum, talk to our team, share your thoughts and connect with the liquid cooling community. What is PWM and how does it work?

July 14, Guides Atila Gobor. Share on social: Facebook Twitter. EK-Vardar mm ER Fan The high static pressure fan, designed and built primarily for highest-performance computer liquid cooling systems. Get yours here! Browse the shop. Learn more about EK products. Go to EK Shop. Check out our fully water-cooled prebuilt PCs.