The stepless speed governor output voltage range of 2.5 v to 8.0 v between the smooth change, the amount of free air set and a range. Clockwise twist knob can increase the air volume, counterclockwise twist reduce the air volume, and knob with switch function! Stepless Speed Regulation Fan Speed Regulation principle: The non-adjustable fan is a 5 fan motor, while the two-stall fan is the interior has a step-up circuit board, when placed in the second gear, the boost plate be USB 5 v up after the motor, the air volume is big. Module : USB Fan Air Conditioner Strong winds and weak wind adjust freely. Instructions: Plug the speed controller male connector into a mobile phone charger or computer USB charger, then plug the fan plug into the speed controller female connector. Alternatively, use a 5.0V Micro USB power adapter.