I. Main parameters of a diode
The technical specifications used to indicate the performance and application range of a diode are called its parameters. Different types of diodes have different characteristic parameters. For beginners, it is essential to understand the following key parameters:
1. Rated forward operating current
This refers to the maximum forward current that a diode can withstand during continuous operation. Because current flowing through the diode causes the die to heat up, and the temperature rises, exceeding the allowable limit (around 140°C for silicon diodes and around 90°C for germanium diodes) will cause the die to overheat and be damaged. Therefore, the rated forward current of a diode should not be exceeded during use. For example, the rated forward current of a commonly used IN4001-4007 type germanium diode is 1A.
2. Maximum reverse working voltage
When the reverse voltage applied across a diode reaches a certain value, it will break down the diode and cause it to lose its unidirectional conductivity. To ensure safe use, a maximum reverse operating voltage is specified. For example, the IN4001 diode has a reverse withstand voltage of 50V, and the IN4007 has a reverse withstand voltage of 1000V.
3. Reverse current
Reverse current refers to the reverse current flowing through a diode under specified temperature and maximum reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the diode. It is worth noting that reverse current is closely related to temperature; approximately, the reverse current doubles for every 10°C increase in temperature. For example, a 2AP1 type germanium diode with a reverse current of 250µA at 25°C will see its reverse current rise to 500µA at 35°C, and so on. At 75°C, its reverse current reaches 8mA, not only losing its unidirectional conductivity but also potentially causing overheating and damage. Conversely, a 2CP10 type silicon diode has a reverse current of only 5µA at 25°C, and even at 75°C, the reverse current is only 160µA. Therefore, silicon diodes have better stability at high temperatures than germanium diodes.
II. Main Applications of Diodes
Thanks to the tireless efforts of scientists over the years, the application of light-emitting diodes (LEDs) has gradually become widespread. Currently, LEDs are widely used in indicator lights of various electronic products, light sources for fiber optic communications, indicators in various instruments, and lighting. Many characteristics of LEDs are unmatched by ordinary light-emitting devices, including safety, high efficiency, environmental friendliness, long lifespan, fast response, small size, and robust structure. Therefore, LEDs are a light source that meets the requirements of green lighting. Currently, LEDs are widely used in many fields; some of their main applications are introduced below:
(1) Applications in electronic products
Light-emitting diodes (LEDs) are commonly used in electronic products as backlights for screens or for display and lighting applications. From large LCD TVs and computer monitors to media players such as MP3 and MP4 players and mobile phones, LEDs are used as backlights for their displays.
(2) Applications in automobiles and large machinery
Light-emitting diodes (LEDs) are widely used in automobiles and heavy machinery. They are used in turn signals, interior lighting, instrument lighting, headlights, turn signals, brake lights, and taillights in automobiles and heavy machinery. This is mainly because LEDs have a fast response time and a long lifespan (generally, the lifespan of LEDs is longer than that of automobiles and heavy machinery).
(3) Application in coal mines
Because LEDs offer advantages over conventional light-emitting devices, such as higher efficiency, lower energy consumption, longer lifespan, and stronger luminous intensity, they are used in miners' lamps and underground lighting equipment. Although not yet fully widespread, they will soon be commonly used, and LEDs will replace conventional light-emitting devices in coal mine applications.
(4) City decorative lights
In today's bustling commercial era, neon lights are an important symbol of urban prosperity. However, neon lights have many drawbacks, such as a short lifespan. Therefore, replacing neon lights with light-emitting diodes (LEDs) offers numerous advantages. Compared to neon lights, LEDs not only have a longer lifespan but also offer energy savings, ease of driving and control, and require no maintenance. The replacement of neon lights with LEDs is an inevitable outcome of the development of lighting equipment.
