作者：Blade

How to measure the LED junction temperature for LED street lighting projects

 

How to measure the LED junction temperature for LED street lighting projects 

 

We know that the LED street lighting projects is a semiconductor diode, the same as a volt-ampere characteristic, and all diodes and semiconductor diode volt-ampere characteristic of a temperature characteristic. Its characteristics when the temperature rises, the volt-ampere characteristic left.

 

To illustrate how estimates of LED junction temperature. To LED street lighting projects installed inside the radiator, and is a constant current drive power. Should connect to the LED to the two line leads. Put in power before the voltmeter connected to the positive and negative terminals of the output (LED), then connect the power to take advantage of LED heat up before, immediately read the readings of the voltmeter, which is equivalent to the value of the V1, and then at least 1 hour, it has reached thermal equilibrium, and then measured once, the LED voltage across, which is equivalent to V2. These two values ​​subtract the obtained difference. Be 4mV removal, you can come to a junction temperature. In fact, the led high bay lighting is mostly for a lot of series and then parallel, that does not matter when the voltage difference is shared by many series of LED and contribution, so take this voltage difference is divided by the number of LEDs in series is again divided by the 4mV, you can get to its junction temperature. For example, the LED is a 10 string 2 and the first measured voltage is 33V, measured after the second thermal equilibrium voltage of 30V, the voltage difference of 3V. This figure is first divided by the number of LEDs in series (10), and get the 0.3V, divided by 4mV can be 75 degrees. Assumes that the boot before the ambient temperature is 20 degrees, so that when the junction temperature should be 95 degrees.

 

 

How to extend the life of LED chips used in led high power bulbs

 

How to extend the life of LED chips used in led high power bulbs

 

Here we are not prepared to discuss the problem of how to design a radiator, but to discuss a radiator cooling effect is relatively good question. In fact, this is a junction temperature of the measurement problem, if we can measure the junction temperature of a radiator that can be achieved, then not only can compare the radiator cooling effect, but also know that using this radiator can achieve led high power bulbs life.

 

Junction temperature appears to be a temperature measurement, but the junction temperature to be measured inside the led high bay, we can not take a thermometer or thermocouple into the PN junction to measure its temperature. Of course, the case temperature can still be measured with a thermocouple, and then given thermal resistance Rjc (junction to case), one can calculate the junction temperature. But after a good radiator is installed, the problem becomes complicated by the Because usually the led high power bulbs is soldered to the aluminum plate, aluminum plate installed on the radiator, if only measuring the temperature of the radiator shell, then to calculate the junction temperature must know a lot of thermal resistance value of. Including Rjc (junction to case), RCM (housing to the aluminum plate, which should include the thermal resistance of the film printed version), Rms (aluminum plate to the radiator), of Rsa (radiator to the air), which has a data inaccurate will affect the accuracy of the test. Figure 3 shows a schematic diagram of the LED to the various thermal resistance of the radiator. Merged a lot of thermal resistance, and its accuracy is more restricted. In other words, the radiator surface temperature to infer from the measured junction temperature accuracy is even worse.

The light decline of RGB LED downlight

 

The light decline of RGB LED downlight

 

Everything has to happen, the process of development and demise of the RGB LED downlight is no exception, there is a certain life. Early only flashlight LED table lamp such gifts, time spent not long life issues. The LED has widely used in outdoor and indoor lighting, especially high-power LED lights, its power, high fever, long working hours, and life issues are very prominent. The past that the RGB LED downlight life must be the myth of 100,000 hours seems completely shattered. So in the end where the problem is it?

 

Most of the white LED has been irradiated by the blue LED yellow phosphor. There are two main reasons caused by the LED light failure, a blue LED’s light fades, the blue LED light failure than red, yellow, green LED. There is also a phosphor light failure, phosphor decay at high temperatures is very serious. Various brands of led high bay light failure is different. Usually LED manufacturers are given a standard set of light decay curve.

 

RGB LED downlight light decline and its junction temperature, the so-called junction temperature is the temperature of the semiconductor PN junction, the junction temperature the higher the sooner the light fades, that is, the shorter the life. Can be seen from the chart, if the junction temperature of 105 degrees, the brightness dropped to 70% of the life of more than 10,000 hours, 95 degrees there is 20,000 hours, while the junction temperature cools to 75 degrees, there are 50,000 hours life 65 degrees can be extended to 90,000 hours. Extend the life of the key is to reduce the junction temperature. However, these data are only suitable for the Cree LED. Not suitable for other LED.

 

 

LED industry increased 42% in the first quarter,led high hat bulbs companies jointly seek breakthroughs

LED industry increased 42% in the first quarter,led high hat bulbs companies jointly seek breakthroughs

Recently, the lighting in the United States to join hands with Japan’s Toshiba Lighting appearance, both sides announced that LED lighting products and technology to achieve the strategic partnership. Since then, the lighting of the United States following the March 2011, the Shanghai Hotel Show to launch the first batch of LED products, LED lighting products and technology a big step forward step; At the same time, led high hat bulbs, the United States also became Toshiba Lighting the largest partner in China.
Insiders said that with the accelerated pace of China’s lighting industry, “powerful combination” has become a lot of new ways of lighting fast break. The beautiful lighting and Toshiba entered into a strategic cooperation, not only can effectively promote the beauty of exploration and development of sophisticated commercial lighting market, led high hat bulbs,but will also further promote China’s LED industry chain and technology upgrades, the cooperation between the two sides will open a common win a new situation in the era of the LED lighting.
In recent years, China’s LED lighting industry is growing rapidly. From the China Association of Lighting statistics show that only 2012 first quarter, China LED applications, the output value reached 19.9 billion yuan, led high bay, an increase of 42%. China Illuminating Engineering Society executive vice president and secretary general of Xuhuai said: “In the case of energy saving by the unprecedented attention, the country has LED lighting as a key development areas, led high hat bulbs,it has become one of the most important changes of the Chinese lighting industry.”
However, the rapid development of the market at the same time, China’s lighting industry, lack of core technology, the lack of innovation capability has become more prominent.”On the whole, there are still about two years the gap between China and the world-class.” Feng-Yi Jiang, vice president of the Nanchang University believes that “many developed countries, developing countries and regions in the world are accelerating the semiconductor lighting technology and industrial development, led high hat bulbs,technically, still in the second echelon. “

Constant voltage supplier is not suitable for mains LED lights

 

Constant voltage supplier is not suitable for mains LED lights

 

Many a variety of fallacious argument on this issue, it was said: the volt-ampere characteristic of the LED, the voltage is set, the current set. So the constant voltage and constant current effect is the same. Some people say that the constant voltage power supply mains LED lights in parallel should be used, and the LED constant current power supply should be used in series; Some people say that, because the mains LED lights constant current devices, so use constant current power supply; Some people say that using electricity supply should be a constant voltage power supply should be used when using battery power, constant current power supply. As for why such a request, it seems, who also did not understand.

 

So, what should be a constant voltage power supply, or a constant current power supply?

 

First look at the LED in the end is what kind of device. LED brightness is proportional to its forward current, and some of the LED structure determines its cooling power. Most LED will give the rated current, such as Φ5 20mA 1W 350mA … and so on, but that does not mean that the LED can only work in those rated current, but does not mean that the led high bay light is a constant current devices. For example, the Cree 1 watt LED and 3-watt LED is the same model, the current increased from 350mA to 700mA power from 1W to increase 3W, so the mains LED lights can be any value between 350-700mA.

The application of constant current driver in solar LED street lamps

 

The application of constant current driver in solar LED street lamps

 

Although there are many methods of use of solar energy are not suitable for China’s national conditions, but like the ultra-high-power solar LED street lamps, the family roof, power generation, only the most simple and most easily implemented solar street lights. The total number of street lights in China more than 100 million, 60 million into a solar street lighting, the annual savings in electricity generating capacity of more than one of the Three Gorges Hydropower Station. Future annual increase of 20 million street lights to switch to solar street lights, three years down a Three Gorges Hydropower Station. Its energy-saving effect is very impressive, but totally does not require launching a campaign to mobilize the country’s power to build, and this launch of local governments at all levels of strength and the power of the enterprises concerned can be completed.

 

The installation of solar street light is also very simple, almost as if planting trees, dig a pit and buried in the family to stay. Unlike the AC lights, Cable-laying and construction of transformer room, dug maintenance well … Although the cost of the cost of a single solar LED street lamps than ordinary high-pressure led high bay lamp is more expensive, but considering the overall cost of the laying of cables, the two are similar. Coupled with substantial annual savings on future electricity, can be said that the savings in electricity of solar street lamps in 2012 can make up the difference, after the savings in electricity is net income.

The selection of various constant current sources in solar powered led street lights

 

The selection of various constant current sources in solar powered led street lights

 

Constant current source in the solar powered led street lights can be divided into the boost, buck, buck three kinds: the so-called step-up its output voltage is higher than the input voltage. Buck output voltage is lower than the input voltage. Buck is to automatically adjust its mode of operation according to the input voltage lower or higher than the output voltage boost or buck.

 

In the solar powered led street lights, commonly used lead-acid batteries as energy storage device, its voltage is typically 12V or 24V. The required output voltage is connected to the LED structure is determined. In order to make all LED forward current, typically in series with each LED, then the required output voltage is the sum of all series LED forward voltage. For example, suppose that the 10 LEDs in series (Figure 9a), the sum of the forward voltage of about 10×3.3V = 33V. In fact, LEDs produced by various manufacturers vary, but also different between each LED. Therefore, the total of 10 led high bay lights forward voltage is not the same. In fact, the constant current source, the constant current rather than voltage. So, do not need to know the exact value of the sum of the forward voltage, and as long as the higher or lower than the input voltage can be. Here, 12V or 24V battery, it requires a boost type constant current source.

 

Sense resistor to be as small as possible, in order to avoid the above power consumption. As low as possible for the fact, which means that its internal reference voltage. For chip designers have a certain degree of difficulty. If the reference voltage of 0.1 volts, is a very good chip, this time, the external sense resistor with a very small value, which means the entire system is highly efficient.

Shopping malls of Energy-saving supermarkets taste the sweetness of using the led light

Shopping malls of Energy-saving supermarkets taste the sweetness of using the led light

Ms. Zhang went into Wal-Mart Dajiaoting shop, feel the soft, light and feel very comfortable. She looked up and found the tube by a small white spot in the dolphin, very bright but not dazzling.
“We switched to LED lighting, a total of more than 1300 sets of LED lights, a year could save 150 000 kWh, equivalent to the electricity consumption of the 40 families a year.”Wal-Mart’s regional general manager of operations Chen Shih said the supermarket operator electricity and water, the led light, is one of the biggest expenses, led high bay, so the application ofenergy-saving facilities commercial enterprises is very positive.
LED lamp energy saving effect is remarkable, and the initial investment is great, but in the long run, this energy-saving money worth spending. At present, Wal-Mart Dajiaotingshop, Wangjing stores have switched to LED lights. The Wangjing energy flagship store in the return on investment cycle of 2-3 years.
LED lights not only energy saving, but also high than the grille lighting 20% is not onlyhigh brightness, the led light, its light is very soft, is not dazzling the guests feel very comfortable.Moreover, compared with the grille, LED lights without UV radiation.
Interestingly, the long standing salesperson feel light, traffic again, did not so sultry. It turned out that 30% of each LED light to release the heat only Grille, which means thatthe mall at room temperature than the low Grille 2-3 degrees Celsius. This means that theLED lights can also store the “indirect energy saving, less air conditioning cost savings.

Carrefour Majiapu store fresh areas, freezers longer exposure, but fitted with a glass door. Through the glass door, the led light, Aunt Jiang bullish on commodities, and then opened the door, took a bag of frozen dumplings into the shopping cart, shutting the freezer door.

“Whose refrigerator took things on the closing, the only supermarket freezer before the open door, the led light, think of all distressed.” Aunt Jiang said.

Solar LED street lighting is an important factor in market

 

Solar LED street lighting is an important factor in market

 

We know that the global lighting electricity consumption accounted for 20 percent of all electricity, of which a large part in solar LED street lighting. China is no exception. According to the statistics China has installed lights about as much as 200 million. The street lamp average power of about 200 watts, assuming the daily opening time of 10 hours, then two units of electricity a day, 365 days is 730 kWh, 200 000 000 146 000 000 000 kWh. The full production of 26 units of the Three Gorges Hydropower Station, China’s largest hydropower station, the annual generating capacity to 84.7 billion kWh of electricity. All the street lamps which consumes huge quantities of about 2 of the Three Gorges power stations. This is not a small figure.

 

Moreover, now the street lights are still 20 million a year increase. But at the moment almost 90% of high-pressure sodium lamp. While its luminous efficiency is still high, but its short life, low power consumption, low color temperature, color rendering is poor, but also contain mercury and other toxic substances in the future, sooner or later be eliminated.

 

Since the Ministry of Science and vigorously developing LED lights Ten thousand ten cities “program. Solar LED street lighting are now in full swing speed high-speed development. Unfortunately, more than 90% of the “Ten City, 10000 or using the AC LED lights, or the transformation of the existing high pressure sodium lamps for led high bay lights. According to conservative estimates, the total number of 10 City, 10000, plans will be more than 2 million, but only one tenth of the total number of new street lights every year. As previously said that, if the annual increase of 20 million are using solar energy, then its total power will reach.

Improved electricity efficiency in constant current module LED household lights

 

Improved electricity efficiency in constant current module LED household lights

 

We know that all LED constant current power supply, but a lot of street lights manufacturer most come looking for a suitable constant current module LED household lights has been designed. Does not know that this design method will have problems, at least makes this design is not the best. May also want to re-design of the LED household lights module.

 

Often receive customer telephone inquiries, and your constant current driver module is able to bring much power? This problem is that it is impossible to answer. Because of the constant current module with how much power is related to many factors. From the constant current module itself, which is, of course, the current drive capability of the driver chips and cooling requirements and heat dissipation conditions. Yet even these have been finalized, for example, has been selected SLM2842 This is a constant current module, then his ability to drive seems to be completely sure! It is not true! Although it limits the drive capability can know, such as its maximum switching current, the maximum input current, the maximum input voltage and maximum output voltage. However, a constant current drive power modules In addition to its cooling capacity, the most important and its working efficiency. While the efficiency of its work and a lot of external factors, especially the user to usage. So when the design or selection of the LED household lights module is necessary to consider the requirements and characteristics of the constant current source.

 

All the power of the led high bay lamp are almost on the market with built-in. The so-called built-in power on the tube inside. The biggest advantage of this built-in can be made to replace the existing fluorescent tubes directly, without having to make any changes to the original circuit. Therefore, the shape of the built-in power usually do grow bar in order to go into the semi-circular tube.