Our common cooling fans have two wires, red and black are power lines, the red wire is positive, the black is negative, collectively known as red positive and black negative, but as users have higher and higher requirements for cooling fans, cooling fans are constantly upgraded and revised to three and four wires. Let’s first discuss the role of the third wire of the cooling fan.
The third and fourth wires are the functional signal lines of the cooling fan. One is the RD alarm signal and the other is the FG speed measurement signal. The RD alarm function is a rotation detection function. When the cooling fan is running, the signal pin outputs a low level and outputs a high level when the rotor is blocked; the FG speed measurement signal is an open collector output connected to a “pull-up” resistor and a compatible reading device input power voltage. This output provides a square wave signal that is a frequency generator or output tachometer.
There are also PWM speed regulation signals and temperature control signals. When the temperature control function signal is applied, the speed of the fan is controlled by the temperature when the cooling fan is running, and different temperatures correspond to different speeds. The PWM speed regulation function can use frequency and high and low voltage levels to control the fan speed. Under this function, the frequency can be adjusted from -, the high level voltage range can be adjusted from 3V~, and the low level range is less than or equal to 0.8V. The fan speed can be linearly controlled by adjusting the “duty cycle” until the fan reaches its maximum speed.