The Three Major Functions of Cooling Fans

The Three Major Functions of Cooling Fans

1. PWM (Pulse Width Modulation)

Function Principle
PWM, or Pulse Width Modulation, refers to a technique where the frequency (period) of a pulse signal remains constant, while the conduction and cutoff periods of the pulse are adjusted to vary the fan speed. This achieves the goals of energy saving and noise reduction.
The fan's driver circuit receives a PWM signal from the controller. The duty cycle (the ratio of pulse width to period) of this signal determines the average supply voltage of the fan motor, thereby controlling its speed.

Application Scenarios

• In computer motherboards: The motherboard dynamically adjusts the PWM signal's duty cycle based on the CPU temperature, precisely controlling the fan speed. When the CPU temperature is low, the fan speed is reduced to minimize noise; when the temperature rises, the speed increases to enhance cooling performance.

• In industrial and communication equipment: PWM-based fan speed control is widely used to meet the varying cooling requirements of different devices under different operating conditions.

2. RD (Reverse Detection / Alarm Signal)

Function Principle
The RD function, also known as the ALARM signal, monitors the fan's rotation direction. When the fan operates normally, the RD signal remains at a low level; if the fan is locked or reverses due to malfunction, the RD signal switches to a high level, triggering an alarm.
By monitoring the RD signal's voltage level, the system can determine whether the fan is running normally or has stalled. If the fan reverses, the RD signal changes accordingly, alerting the motherboard or control device.

Application Scenarios

• In server chassis and other high-performance devices: Correct fan rotation is critical for effective heat dissipation. If a fan reverses, it may fail to expel heat properly, potentially causing hardware overheating and damage. The RD signal allows the system to detect such issues promptly, notifying administrators for inspection and repair.

3. FG (Frequency Generator / Speed Feedback)

Function Principle
The FG function outputs a square wave signal, where the frequency of the signal corresponds to the fan speed. This allows the system to monitor the fan's rotational speed in real time.

Application Scenarios

• In electronic device cooling: The FG signal is used to monitor fan speed, ensuring that high-power components like CPUs and GPUs operate within safe temperature ranges. For example, a computer motherboard can dynamically adjust fan speed based on the FG signal—lowering it during low loads to reduce noise and increasing it under heavy loads for better cooling.

• In industrial control equipment: The FG signal helps monitor fan status, preventing overheating that could lead to production line shutdowns or data loss.

Summary

The three key functions of cooling fans—PWM (speed control), RD (fault detection), and FG (speed feedback)—work together to ensure efficient, reliable, and safe thermal management in various applications, from consumer electronics to industrial systems.