Monday, January 3, 2011

【 Weak current College 】 how to extend the high brightness LED life 】



You only need to join simple, low cost of electronic components, you can protect valuable high-brightness LED. This thermal protection design helps lighting designers achieve smaller, lower cost of production.

Needless to say, the light-emitting diodes for durable and long-life characteristics in the different application handy, brings obvious benefits. However, when a high power LED to high luminosity, the heat will become a key issue. In fact, enter the power LED is only less than 20% into light, the remaining 80% is transformed into heat energy. This is indeed a lighting system designers need to overcome the problem.

If lighting system implementation is poor, even the most perfect thermal design, it is difficult to develop their full potential, bring the real purpose. Keep safe LED operating environment, reduce the heat dissipation on LED life impact, they fell for driving LED's electronic components.

In fact, as long as we take a look at high-luminosity LED manufacturer's component product specifications, it is not difficult to determine the main design requires attention, and that parameter at a high temperature operation on these devices.

The actual lifetime of LED and power dissipation and LED the temperature of the nodes are often inversely. Manufacturers can appear in different temperatures run Tj80 million hour mean time between failures (MTBF). In practical system, LED by the failure would not necessarily lead to big problems, but in the heat, and Tj also rose to 120 ° c or more systems, LED's life would be substantially reduced. In some extreme cases, the LED will immediately fail.

Thermal design can introduce super compensation function, in order to counter the most adverse circumstances. However, in some cases, this is impossible. The downlight, for example, generally installed in the insulation of the ceiling space between the layers. This space is not only impede cooling, there is no adequate place to install additional cooling facilities.

Relative luminosity also inversely with the junction temperature. As data changes, the manufacturer estimated maximum junction temperature of the light output is reduced by 30%.

Similarly, lumens maintenance effects and junction temperature also inversely. At 70 ° c junction temperature, a LED operation for more than 5 million hours, usually loss 30% photometric output; temperature higher loss will be greater, but formal data has not yet been made public.

Therefore, the designer's most important objective is the dissemination of the LED heat as soon as possible, thus keeping the junction temperature maximum ratings following, prevents premature failure.

In General, used to produce the desired LED current electronic devices, you can easily introduce detect overheating method that effectively reduce LED drive current, maintain stable operating temperature. Although the light output is somewhat diminished, but LED "vitality" was very strong, long term operation.

To design an LED driver circuits, for example, the buck converters is equipped with temperature control function, driving current up to 1 ampere, supply voltage between 4 volts to 6 volts. The circuit uses a 150 k Ω N T C thermal control tube temperature detection, the location of the component and LED to maintain close contact with the heat. Current flows through the thermal control tube will be doubled, and the sum of peak current Exchange, thus adjusting the led current.

You only need to join simple, low cost of electronic components, you can protect valuable high-brightness LED. This thermal protection design helps lighting designers achieve smaller, lower cost of production.

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