The circuit we give is a circuit that uses a common 1N4148 diode as a sensor to control the temperature of a component or any place that is subject to an undue temperature rise. This circuit, shown in the figure, starts a fan motor that starts when the temperature exceeds a value that will be set in P1. The sensitivity will be higher the higher the value that can be adjusted in P1 to obtain the trigger threshold. 470 k ohm trimmers are the smallest recommended for applications with a transistor, but the best ones are 2 M ohms and even 4.7 M ohms, when maximum sensitivity is obtained. of forced ventilation for an audio amplifier that has power transistors mounted on a heatsink.
