In addition to the common PWM speed control and FG speed detection and RD stop alarm, what other protective functions do cooling fans have? Next, let's understand their functions together. First, motor signal detection: 1, FG: speed measurement signal, real-time detection of motor current speed continuous square wave signal. 2. RD: Alarm signal, fan normal low level, output high level when stop. Motor protection: 1. LD function of cooling fan: This is an open collector function, which is the same hardware function as the FG function mentioned above. When the fan runs at conventional speed, the output is low, and when the fan runs below 70% of the target rated speed, the alarm starts. The reason is that low speed operation may aging or reduce voltage. 2. OVP function of heat dissipation fan (over-voltage protection). The voltage exceeds 20% of the working voltage and the fan stops running. 3. Heat dissipation fan SS function (soft start): When the fan is powered, the current increases gradually from zero until the fan reaches the rated current. 4. Cooling fan CL function: Under this function, during the lock-in period, the current is limited. 3. Motor speed control methods are as follows: 1. PWM: speed control signal line. PWM function can use square wave signal to change duty cycle to linearly control fan speed. 2. TC: Temperature control signal line. When this function is applied, the speed of fan is controlled by temperature. By detecting the ambient temperature, the speed of fan can be controlled intelligently. 3. VC: DC voltage signal control. Under this function, the speed of the fan is controlled according to the voltage signal. 4. CC: Current source signal control. Under this function, speed can be controlled by applying external current source signal. 5. CS: Fixed constant speed function, which is a very important function, because it allows the fan motor to operate safely in a very large power supply voltage range. 6. RC function of cooling fan (manual control variable resistor): When applying this function, speed can be controlled by using an external variable resistor.