Introduction to the basic parameters of LED lamp chip
As an electroluminescent P-N junction device, the characteristics of the LED can be described by the electrical parameters of the P-N junction and the optical parameters of a light-emitting device.
1. The volt-ampere characteristic is an important parameter describing a P-N junction device. It is an important indicator of the performance of the P-N junction and the quality of the P-N junction manufacturing process. The so-called volt-ampere characteristic is the characteristic that the current flowing through the P-N junction changes with the voltage, which can be vividly displayed on the oscilloscope.
A complete volt-ampere curve includes forward and reverse characteristics. Generally, the reverse characteristic curve changes steeply, and when the voltage exceeds a certain threshold, the current will rise exponentially. Generally, three parameters of reverse breakdown voltage, reverse current and forward voltage can be used to describe the volt-ampere characteristic curve. The forward voltage VF refers to the voltage drop between the two terminals of the device under the rated forward current. This is not only related to the band gap of the material, but also indicates the volume resistance and ohmic contact resistance of the P-N junction. The size of the VF reflects the pros and cons of the electrode production to a certain extent. Relative to a forward current of 20 mA, the VF value of red-yellow LEDs is about 2 volts, while the VF value of GaN-based blue-green LED devices is usually greater than 3 volts. The reverse leakage current IR refers to the reverse current value flowing through the device under a given reverse voltage. The magnitude of this value is very sensitive to the quality of the device. Normally, under a reverse voltage of 5 volts, the reverse leakage current should be no more than 10 microamperes. Excessive IR indicates poor junction characteristics. The reverse breakdown voltage means that when the reverse voltage is greater than a certain value, the reverse leakage current will increase sharply, reflecting the reverse withstand voltage characteristics of the device. For a specific device, the standard for the magnitude of the leakage current is different. Under stricter circumstances, the reverse leakage current is required to be no more than 10 microamperes under the specified voltage.
Second, in addition to electrical characteristics, a series of optical parameters need to be used to describe the performance of LED devices, among which the more important parameters are the peak wavelength and light intensity of the device. Visible light belongs to the category of electromagnetic waves, and wavelengths can usually be used to express what the human eye can feel. The radiation energy of visible light generally has a wavelength range of 380nm-760nm. The longer the wavelength, the lower the corresponding photon energy and the redder the color of the light. When the wavelength of the photon becomes shorter, the light will gradually change from Red turns to yellow, then turns green to blue, until it turns purple. For an LED device, the light emitted will expand at the peak λP, and its wavelength half-width is usually 10-30nm. The smaller the half-width, the purer the material of the LED device, the more uniform the performance, and the integrity of the crystal. The better the sex. Light intensity is another important parameter to measure the performance of LEDs, usually represented by the letter Iv. The definition of light intensity is that in a given direction, light has 1 stream per unit solid angle.
The light of bright is 1 candela, and its unit is expressed by candela (cd). The relationship can be characterized by formula (6-1):
Iv=dφ/dΩ (6-1)
In the formula, the unit of φ is lumens, the unit of Iv is cd, and dΩ is the unit solid angle, and the unit is degree. The normal light intensity of an ultra-bright LED chip is generally between 30-120mcd. After being packaged into a device, its normal light intensity is usually greater than 1cd.
Luminous flux is a more objective parameter for judging the luminous efficiency of LEDs. It represents the amount of light energy emitted by the electroluminescent body in a unit of time, in lumens (lm). Generally, the luminous efficiency of incandescent lamps and fluorescent lamps are 15lm/w and 60lm/w respectively. The greater the power of the bulb, the greater the luminous flux. For a high-performance LED device, the luminous efficiency is 20lm/w, and the laboratory level can reach 100lm/w. In order for LED devices to be used for lighting faster, the luminous efficiency of LED devices must be further improved. It is estimated that after 10 years, the luminous efficiency of LEDs can reach 200lm/w. By then, mankind will usher in a new era in which solid-state light sources completely replace traditional light sources.
