The circuit diagram shows. The IC is a NE555 time base circuit, RP3 is a temperature-regulating potentiometer, its sliding arm potential determines the IC trigger potential V2 and threshold potential Vf, and V5=VF=2VZ. 220V AC voltage by c1.r1 current limiting pressure relief, d1.d2 Rectifier, C2 filter, DW voltage stabilizer, to obtain about 9V voltage for IC. The power supply is plugged in at room temperature, and the temperature increases gradually because the V2 electric wire is energized and heated. Thermal sensor BG1 with the increase of temperature, its penetration current ICEO increase, V2. V6 raised. When V2>VZ,V6≥VF, IC Flip, ③ foot into low potential, BCR cutoff post Office hot wire Stop heating, temperature began to gradually decline, BG1 iceo gradually reduced, V2. V6 reduced.