The utility model relates to a control circuit for a heat radiating fan, particularly a temperature control and a PWM composite control circuits for a heat radiating fan. The temperature control and the PWM composite control circuits for the heat radiating fan comprise a temperature control circuit and a PWM control circuit. The utility model is characterized in that the temperature control and the PWM composite control circuits for the heat radiating fan is provided with a temperature control and PWM compatible rotational speed regulating control circuit which is formed by connecting the temperature control circuit, the PWM control circuit and a temperature control common amplification circuit in series. A temperature control rotational speed type, a PWM control rotational speed type and a PWM composite control rotational speed type are simultaneously operated, and the performance is stable. The utility model has the function of power supply reverse connection protection, the fan can be at a very good condition when being connected with power supply inversely, and the control circuit for the heat radiating fan also has the function of keeping minimum rotational speed constant. The range of speed regulation for the temperature control can be conveniently changed, the voltage can be changed just needing changing the resistance of a thermal resistor and the corresponding resistance value, and then the functions can be achieved.