Fan Speed Controller

The scheme modulates the speed of a fan directly proportional to the temperature detected by the NTC. LED1 illuminates when the temperature exceeds a certain threshold determined by D1. For supply voltages greater than 13.5V, the role of U2 is to limit the applied fan voltage to about 12V no matter how much the temperature increases. If V1 does not exceed 13.5V, group U2, R5 and R6 will be removed. To adjust the fan speed according to the temperature at different intervals, the R3 must be changed in the 1.5 - 2.5Koms range. Do not forget to heatsink the LMs. Have "FAN"!