Drive LED high luminosity electronic components to extend the life of

There is no doubt that the durability and long life characteristics of LEDs can be used in different applications, bringing obvious benefits. However, when high power LED is applied to high luminosity operation, heat dissipation becomes a key issue. In fact, less than 20% of the power input to LED is converted into light energy, and the remaining 80% is converted into heat energy. This is the lighting system designers need to overcome the problem.

If the poor implementation of the lighting system, even the most perfect thermal design, to the fullest play real use. The responsibility of maintaining a safe LED operating environment and reducing the impact of thermal dissipation on the life of the LED falls on the electronic components used to drive the LED. In fact, if we look at the component specifications high luminosity LED provided by the manufacturer, it is not difficult to determine the need to pay attention to the main design parameters, and that the negative impact on the operation of these devices at high temperature. The actual life of LED is inversely proportional to the power dissipation and the temperature of the LED node. The manufacturer can display an average time between failures (MTBF) of about one hundred million hours operating at Tj80 DEG C. In a practical system, the failure of LED is not necessarily a big problem, but in the lack of heat, and the Tj rose to 120 degrees or more in the system, the life of the LED will be greatly shortened. In some extreme cases, LED more real-time failure. The design of thermal energy can be used to compensate for the worst environment. In some cases, however, this is impossible. The lamp for example, usually installed in the space between the ceiling insulation layer. This space not only prevents heat dissipation, but also does not have enough position to install additional cooling facilities. The relative luminosity is inversely proportional to the junction temperature. With the variation of the data, the manufacturer estimates that the output of the light at the maximum junction temperature will be reduced by 30%. Similarly, the lumen maintenance effect is inversely proportional to the junction temperature. At 70 junction temperature, a LED operation over a period of more than 50 thousand hours, the general loss of photometric output; higher temperatures will be greater losses, but the official data has not been disclosed. Therefore, the most important goal of the designer is to heat the LED as soon as possible, so as to keep the node temperature below the maximum rating to avoid premature failure. In general, the electronic device used to generate the desired LED current can be easily introduced into the method of detecting the high temperature, which can effectively reduce the driving current of the LED and maintain a stable operating temperature. Although the light output will be slightly reduced, but LED's vitality is very strong, long-term operation. With a LED driver circuit design as an example, the buck converter is equipped with temperature control function, driving current up to 1 amps, supply voltage from 4 volts to 6 volts. The circuit uses a 150k NTC thermal control for temperature detection, the position of the component and LED maintain close thermal contact. The current flowing through the heat control will be multiplied and then added to the peak current to regulate the LED current. Simply by adding simple, low-cost electronic components, you can protect the precious high luminosity LED. This technique can be applied on a number of different control systems, and applies to any ZXSC series LED driver IC buck and boost mode of operation. This kind of thermal protection design is helpful to the design of the lighting system to achieve a smaller, lower cost solution.

Source: China Electronics News