Diode is an electronic device made of semiconductor materials (silicon, selenium, germanium, etc.). It has unidirectional conductivity, that is, when direct voltage is applied to the anode of the diode, the diode conducts. When a reverse voltage is applied to the anode and cathode, the diode is turned off. Therefore, the turn-on and turn-off of the diode is equivalent to the turn-on and turn-off of the switch. Diode is one of the earliest semiconductor devices, and its application is very extensive. Especially in various electronic circuits, diodes are reasonably connected with resistors, capacitors, inductors and other components to form circuits with different functions, which can realize various functions such as rectifying alternating current, detecting modulation signals, limiting and clamping, and stabilizing power supply voltage. No matter in common radio circuits or in other household appliances or industrial control circuits, traces of diodes can be found.