Electronic – What does FG stand for


I have an old 12V cooler master fan that I am converting into a fume extractor for soldering and am connecting it to a standard 12v computer power supply. I am trying to wire it and am confused about one thing.

On the fan's label it has a coding for the different wire colors (red, black, and white) and it says:

red +

black –

white FG

I have looked up FG on google all over the place but can't seem to find anything that says what it stands for. I was thinking that it might be "Ground" but then what would the black negative wire be? Maybe I just have a fundamental misunderstanding (pretty new to all of this electronics stuff)

I did connect the black wire on the fan to a black wire on my power supply and the red wire on the fan to a yellow wire on the power supply (white wire connected to nothing) and it turned on and seemed to be working fine but I want to make sure that this is actually a correct wiring and isn't going to cause any problems in the future.

Best Answer

FG stands for Frequency Generator (or Feedback Generator), it has an output with a frequency proportional to the fans speed. It is used by the CPU to determine the fans speed.

Some (older) fans have an extra winding internally and the FG signal is a sinusoid with both amplitude and frequency proportional to fan speed.

Modern fans almost exclusively use a Hall-Effect sensor and the signal is an open-collector square-wave signal where the frequency is proportional to fan speed. Peak voltage is determined by the magnitude of the power supply that feeds the pull-up resistor.