What are the functional requirements needed? – Optional functions

There are some functions that are needed by customers from time to time. Most commonly asked functions are AR (auto restart), RD (rotation detection), FG (frequency generation), speed control, etc. Here below a brief summary of each function is made for your reference. For more information regarding detailed specification and applications, please contact ARX.

Auto Restart:

In the event that the fan (impeller) is blocked by expected or unexpected external means, a signal sent will be sent from circuit to IC such that the power is switched to stand by status. Meanwhile, a capacitor is charged as a reserved source of power for rebooting the fan. By applying this function, the temperature of the fan can be kept at lower level in case the fan is stopped with power on.

Alarm Signal:

Alarm signal is used to tell the status of operation. There are two kinds of alarm signals for your choice.

A. RD (Rotation Detection)

RD sensors are used to provide the signals of operating status of fan motor. Whether the fan motor is running or stopped can be detected with an output of high (low) or low (high).

B. FG (Frequency Generation)

Signal is an open collector. This is also called tachometer signal, used to detect the speed of the fan. The two pulses per revolution comes with 50% duty cycle.

Speed Control:

A. Temperature Control

The thermal speed control option varies the speed without the need of any external input. This option uses a thermistor to monitor the temperature and regulate the speed accordingly. The thermistor will change its resistance at different temperatures, thus creating a variable voltage divider circuit at the adjust leg of the voltage regulator. The fan will automatically adjust its speed to optimize the airflow to the surrounding temperature. The fan will operate at its maximum speed and minimum speed when detecting specific high (temperature) or specific low (temperature), respectively. Between the two temperature limits, the fan speed will vary almost linearly with temperature.

B. PWM (Pulse Width Modulation)

Pulse Width Modulation (PWM) is a technique for controlling analog circuit with a processor’s digital output. In other words, PWM is a way of digitally encoding analog signal levels. The PWM fan speed control method adds an extra 4th wire to the connector. The 4th wire is a Pulse Width Modulation (PWM) input that provides a duty cycle to the fan. For example a 60% PWM duty cycle is a perfect square wave where 60% of the signal is high and 40% of the signal is low. A 60% PWM duty cycle applied to the 4th wire of the fan will result in a fan speed of 60% the total maximum fan speed. That is, if the fan is rated for 5000 RPM max, a 60% PWM duty cycle will result in the fan running at 3000 RPM. An 80% PWM signal applied to the fan is a square wave were 80% of the signal is high and 20% is low resulting in a fan speed proportional to the duty cycle as referenced to the maximum speed of the fan.

(1) FPWM

By means of applying voltage on and off, the amplitude should be equal to the nominal voltage of the fan, the frequency should be held constant and the duty cycle allowed to vary between 0 and 100%.

(2) VPWM

By means of applying voltage on and off


This is a function that can produce a stand by state. The fan will stop its operation when getting the stand by signal. The fan will reboot when the system signals the need for cooling.

D. Others

Functions other than the above can be customized upon request. Please contact us when needed.