LED is called the fourth-generation illumination source or green light source. It has the characteristics of energy saving, environmental protection, long life and small size. It is widely used in various fields such as indication, display, decoration, backlight, general illumination and urban night scene. According to the different functions, it can be divided into five categories: information display, signal light, vehicle light, LCD backlight, and general illumination. Conventional LED lights have shortcomings such as insufficient brightness, which leads to insufficient penetration. The power LED lamp has the advantages of long life and long life, but the power LED has technical difficulties such as packaging. The following is a simple analysis of the factors affecting the light extraction efficiency of the power LED package . Package elements that affect light extraction efficiency 1. Heat dissipation technology For a light-emitting diode composed of a PN junction, when a forward current flows from the PN junction, the PN junction has a heat loss, which is radiated into the air via a bonding glue, a potting material, a heat sink, etc., in the process. Some materials have thermal impedance that blocks heat flow, that is, thermal resistance, which is a fixed value determined by the size, structure, and material of the device. Let the thermal resistance of the LED be Rth (°C/W) and the heat dissipation power be PD(W). At this time, the PN junction temperature rise due to the heat loss of the current is: T(°C)=Rth×PD The PN junction temperature is: TJ=TA+Rth×PD Where TA is the ambient temperature. As the junction temperature rises, the probability of PN junction luminescence recombination decreases, and the brightness of the LED decreases. At the same time, due to the increase in temperature rise due to heat loss, the brightness of the LED will no longer continue to increase proportionally with the current, indicating thermal saturation. In addition, as the junction temperature rises, the peak wavelength of the luminescence will also drift toward the long wavelength, about 0.2-0.3 nm/°C, which is for the white LED obtained by mixing the YAG phosphor coated with the blue chip. Drift causes a mismatch with the excitation wavelength of the phosphor, thereby reducing the overall luminous efficiency of the white LED and causing a change in the white color temperature. For power LEDs, the drive current is generally several hundred milliamperes or more, and the current density of the PN junction is very large, so the temperature rise of the PN junction is very obvious. For packaging and applications, how to reduce the thermal resistance of the product, so that the heat generated by the PN junction can be dissipated as soon as possible, not only can improve the saturation current of the product, improve the luminous efficiency of the product, but also improve the reliability and life of the product. . In order to reduce the thermal resistance of the product, the choice of packaging materials is particularly important, including heat sinks, adhesives, etc., the thermal resistance of each material is low, that is, the thermal conductivity is required to be good. Secondly, the structural design should be reasonable, the thermal conductivity between the materials should be continuously matched, and the thermal connection between the materials is good, avoiding the heat dissipation bottleneck in the heat conduction channel and ensuring the heat is dissipated from the inner to the outer layer. At the same time, it is necessary to ensure that the heat is dissipated in time according to the pre-designed heat dissipation channel. 2. Filling glue selection According to the law of refraction, when light is incident from the optically dense medium to the light-diffusing medium, when the incident angle reaches a certain value, that is, greater than or equal to the critical angle, full emission occurs. In the case of a GaN blue chip, the refractive index of the GaN material is 2.3, and when light is emitted from the inside of the crystal to the air, the critical angle θ0 = sin-1 (n2/n1) according to the law of refraction. Where n2 is equal to 1, ie the refractive index of air, and n1 is the refractive index of GaN, from which the critical angle θ0 is calculated to be approximately 25.8 degrees. In this case, the light that can be emitted is only the light within the solid angle of the space where the incident angle is ≤ 25.8 degrees. It is reported that the external quantum efficiency of GaN chips is currently around 30%-40%. Therefore, due to the internal absorption of the chip crystal, the proportion of light that can be emitted outside the crystal is small. It is reported that the external quantum efficiency of GaN chips is currently around 30%-40%. Similarly, the light emitted by the chip is transmitted through the encapsulating material to the space, and the effect of the material on the light extraction efficiency is also considered. Therefore, in order to improve the light extraction efficiency of the LED product package, it is necessary to increase the value of n2, that is, to increase the refractive index of the packaging material, so as to increase the critical angle of the product, thereby improving the package luminous efficiency of the product. At the same time, the encapsulation material absorbs light less. In order to increase the proportion of the emitted light, the shape of the package is preferably arched or hemispherical so that when the light is directed from the encapsulating material to the air, it is almost perpendicularly incident on the interface, so that no total reflection is produced. 3. Reflection processing There are two main aspects of reflection treatment. One is the reflection treatment inside the chip, and the other is the reflection of light by the encapsulation material. Through the reflection treatment of the inner and outer sides, the proportion of the light flux emitted from the inside of the chip is increased, and the internal absorption of the chip is reduced. Improve the luminous efficiency of power LED products. In terms of packaging, power LEDs usually mount power chips on metal brackets or substrates with reflective cavities. Bracket-type reflective cavities generally use electroplating to improve reflection, while substrate-type reflective cavities are generally polished. In the mode, the plating treatment is carried out under conditions, but the above two treatment methods are affected by the precision and process of the mold, and the reflective cavity after the treatment has a certain reflection effect, but it is not ideal. At present, the substrate-type reflective cavity is made in China, because the polishing precision is insufficient or the metal plating layer is oxidized, the reflection effect is poor, which causes a lot of light to be absorbed after being incident on the reflection area, and cannot be reflected to the light-emitting surface according to the intended target, thereby resulting in the final The light extraction efficiency after packaging is low. 4. Phosphor selection and coating For white power LEDs, the increase in luminous efficiency is also related to the choice of phosphor and process. In order to improve the efficiency of the phosphor to stimulate the blue chip, firstly, the selection of the phosphor should be appropriate, including the excitation wavelength, the particle size, the excitation efficiency, etc., and comprehensive evaluation is required, taking into account various performances. Secondly, the coating of the phosphor should be uniform, preferably the thickness of the glue layer of each light-emitting surface of the light-emitting chip is uniform, so as to avoid local light being unable to be emitted due to uneven thickness, and the quality of the spot can be improved. Summary: Good thermal design has a significant effect on improving the luminous efficiency of power LED products, and it is also a prerequisite for ensuring product life and reliability. The well-designed light exit channel, which focuses on the structural design, material selection and process processing of the reflective cavity, the filling glue, etc., can effectively improve the light extraction efficiency of the power LED. For power-type white LEDs, the choice of phosphor and process design are also critical to the improvement of the spot and the improvement of luminous efficiency. The story of Ethernet began in the ALOHA period. The exact time was after a student named Bob Metcalfe received a bachelor's degree from the Massachusetts Institute of Technology and moved to Harvard University across the river to pursue a PhD. During his studies, he came into contact with Abramson's work, and he was very interested in it. After graduating from Harvard, he decided to stay in Hawaii for vacation before going to Xerox Palo Alto Research Center to work in order to help Abramson work. When he arrived at the Palo Alto Research Center, he saw that researchers there had designed and built machines that would later be called personal computers, but these machines were solitary; he used the knowledge he gained to help Abramson work with his colleague David Boggs designed and implemented the first local area network. The local area network uses a long thick coaxial cable and runs at a rate of 3Mbps. Voip ONU,GPON ONT Pots, FTTH Optical Network Modem,Telephone Port, FXS Port Shenzhen GL-COM Technology CO.,LTD. , https://www.szglcom.com
They named this system Ethernet, and people once thought that electromagnetic radiation could be transmitted through it.
Shared medium
The Carrier Sense Multiple Access (CSMA/CD) technology with collision detection specifies a method for multiple computers to share a channel. This technology first appeared in the ALOHAnet developed by the University of Hawaii in the 1960s, which uses radio waves as a carrier. This method is simpler than token ring network or main control network. When a computer wants to send information, it switches between the following actions and states:
Start-If the line is idle, start the transmission, otherwise skip to step 4.
Send-If a conflict is detected, continue to send data until the min echo receive interval is reached to ensure that all other transponders and terminals detect the conflict, and then skip to step 4.
Successful transmission-report to the higher-level network protocol that the transmission was successful, and exit the transmission mode.
Line is busy-keep waiting until the line is free.
Line is idle-before reaching the maximum number of attempts, go to step 1 to try again at random intervals.
Exceeded the maximum number of transmission attempts-report the transmission failure to the higher layer network protocol, and exit the transmission mode.
Because all communication signals are transmitted on the shared line, even if the information is only sent to one of the terminals (destination), it will be sent to all computers on the line in the form of broadcast. Under normal circumstances, the network interface card will filter out the information that is not sent to itself, and will send an interrupt request to the CPU when it receives the information whose destination address is its own, unless the network card is in Promiscuous mode. This "one talk, everyone listen" characteristic is the security weakness of the shared medium Ethernet, because a node on the Ethernet can choose whether to listen to all the information transmitted on the line. Sharing cables also means sharing bandwidth, so in some cases the speed of Ethernet may be very slow, such as after a power failure, when all network terminals are restarted.