"24V DC Cooling Fan" product TC642 style is a switch mode fan speed controller for controlling a brushless DC fan speed. Using pulse width modulation (PWM) to achieve proportional speed and temperature. We can enter the VIN pin connecting a thermistor (or other voltage output temperature sensor), provides the required 1.25V to 2.65V typical fan control voltage, and 0-100% duty cycle of the PWM we can control this, I think how to adjust how to adjust. These products can be a simple resistor divider VMIN input can be set to the minimum fan speed.