What is the wiring of the internal switch of the hair dryer? What's the use of that diode? It is better to have a picture.
Blower switch is a single-pole, two-position and three-state switch, in which one power cord is connected to the knife, the first one is connected to the live wire, the second one is connected to the first one through the diode, and the third one is empty. The function of the diode is to cut off the half-wave, so that the remaining half-wave pulsating DC is equivalent to half of 220 volts, that is, the hot line is energized only half the time, thus achieving the purpose of lossless voltage reduction.