Distinguishing the quality of crystal diodes 3

By utilizing the unidirectional conductivity of diodes, they are commonly used as rectifiers to convert alternating current into direct current, allowing only the positive (or negative) half of the alternating current to pass through, and then filtering with capacitors to form a smooth direct current. In fact, the power supply of many electrical appliances is like this. Diodes are also used as detectors to "detect" useful signals in high-frequency signals. Old radios have a "detection diode", usually using 2AP9 germanium tubes.

There are several types of diodes, and for electronic manufacturing, the following diodes are often used: voltage regulator diodes for voltage regulation, switch diodes for digital circuits, varactor diodes for tuning, and photodiodes. The most commonly seen is the light-emitting diode.

Light emitting diodes are ubiquitous in daily household appliances. They can emit light in red, green, and yellow colors, and come in rectangular shapes with diameters of 3mm, 5mm, and 2 × 5mm. Like ordinary diodes, light-emitting diodes are also made of semiconductor materials and have unidirectional conductivity, meaning they can only emit light when connected to the opposite polarity. The LED symbol has two more arrows than a regular diode, indicating that it can emit light. LEDs are usually used to indicate the working status of circuits. They consume much less power than small light bulbs and have a much longer lifespan. By using light-emitting diodes, electronic display screens can also be constructed. The display screens in stock exchanges are made up of a dot matrix of light-emitting diodes, but because various colors are composed of red, green, and blue, and blue light-emitting diodes have not been mass-produced before, general electronic display screens cannot display true colors.