A 3-terminal voltage regulator can be used as an efficient temperature regulator for a current resistive heating element up to 3 A, as shown in the figure circuit. The sensor is a common NPN transistor of any type that must be mounted in contact with the heating element. Evidently, the temperature of this element should not exceed approximately 100º C, since above that the transistors used as a sensor can be damaged. The resistor may have its value changed depending on the desired temperature and the input voltage must be suitable for the sensor used. The regulator integrated circuit admits equivalent as the LM317 if the element has a current below 1.5 A and must always be mounted on a heat radiator. The same circuit can be modified to control the brightness of an incandescent lamp, in which case the transistor used as a temperature sensor must be replaced by a phototransistor.
