The constant voltage power supply is the important cause of the LED light failure

Shanghai MaoYuHai Long Mao microelectronics co. , LTD.

now we began to realize that light failure is the main reason for the high power LED street light can't work for a long time, also began to recognize the lower light failure is an important way to improve its heat dissipation. In spite of this, from the shenzhen lighting environment management center of all kinds of street lamp test results, there are still most of the street lamp light failure is cannot satisfy the use requirement. After 1200 hours of light light failure, the best is 8%, the worst is 26%, the average of 14%. Test results in accordance with Cree company, junction temperature at 105 degrees, 14% light failure also should be at work for 6000 hours, most of the visible lights junction temperature above 105 degrees.

in figure 1. Cree company LED junction mild droop life test results

may be a lot of companies do not agree with this result, because they think their radiator are carefully designed. The actual situation may also is such, but the test result is also beyond doubt. Where is the problem?

I think that may be the radiator is not designed to be so bad, but it may be because there are some lights is to use the results of the constant voltage power supply.

but why using constant voltage power supply will cause light failure? It sounds like a bit of a fable. But in fact there are so serious. Let's beginning! LED the volt-ampere characteristics of

as we all know, LED is a diode, and the electrical characteristics of diode is the most important is its volt-ampere characteristics. Figure 2 gives the Cree XLamp7090XR - of the company E volt-ampere characteristics.

in figure 2. XLamp7090XR - LED temperature characteristics of volt-ampere characteristic

although it looks like an ordinary diode, but the biggest difference is that its temperature characteristic. Actually all the volt-ampere characteristics of diode has the problem of temperature characteristic, but is that the LED is need special attention. This is because the

2. High power LED working current is larger, 1 w to 0. 35一个,3 - 5 w is 0. 7 w a, 20 to 1. 5 a, 30 w of 1. 75 a, 50 w is 3. 5A。 But could also be someone think, forward current of rectifier diode is also likely to achieve such a great value.

2. 2 LED because the luminous efficiency is lower, so most of the input power is converted to heat, so it is a high fever, do well if the radiator, the junction temperature will rise high.

2. 3 leds, unlike rectifier diode, it is not using general silicon materials, but the use of special materials ( Such as gallium nitride) Is made. So its volt-ampere characteristic temperature characteristic is different from general diode, but to significantly greater than general diode. For example, the general volt-ampere characteristic of diode temperature characteristic of - Mv / 2 ° C, but Cree XLamp7090XR - of the company E temperature of volt-ampere characteristics is high Mv / 4 ° C, than the average diode twice. Produced by high junction temperature problems

3. 1 the LED junction temperature rise high after the first is to reduce light output.

- China lighting network Zhi son

China lighting network