作者：Blade

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.

OFN package for different low voltage led landscape lights

 

OFN package for different low voltage led landscape lights

 

Chip package is also very important, the QFN chip package is clearly better than the chip in a TSSOP package, thermal resistance is much lower. In the purchase of the module should understand the used chip package (as far as possible in a QFN package, to avoid using the TSSOP package).

 

Now give a concrete example to illustrate: if the solar low voltage led landscape lights uses a 12V battery, the load is 8-string 3 and 1W LED load voltage at the output is roughly 26.4V, the current is 1.05A, the output power of 27.7 W. If the 12V battery, the highest time in the voltage is 14.8V, the step-up ratio is 1.78, then do not have the radiator when the QFN package case temperature is about 60 degrees. Acceptable, but when the battery voltage drops to 10.8V, the step-up ratio becomes 2.44 times, and this time the shell temperature will rise to more than 70 degrees, if the TSSOP package case temperature will rise to about 85 degrees is not allowed!

 

In addition to the need to consider the case temperature, but also consider the maximum input current. SLM2842 the maximum input current of 3A. In the calculation of the maximum input current, we must consider the efficiency of the constant current module itself. Assumed to be 90% at the same time assumes that the output power is 32W, divided by 0.9 is 35.5W.

 

The number of series low voltage led landscape lights should be less than 10, this is because LED lamps have a safety requirements. Voltage led high bay lamps shall not exceed the maximum safety extra low voltage (SELV) according to EU standards of the IEC 61347-2-13 (5/2006), the requirements for DC or AC powered LED module, which is the work output voltage ≤ 25 Vrms (35.3 Vdc), so the total number of series LEDs is not more than 10

Constant current control module for LED street lamps

 

Constant current control module for LED street lamps

 

In the case of electricity, of course, the best AC-DC direct constant current output of the program.

This program can only provide a small power output (<40W) only the United States Power Integration company TOP250YN can provide 75W power output of the program. The circuit is very complicated, expensive, and low flexibility, which is not popular in mains led lighting applications.

 

LED street lamps direct constant current output power supply, but usually only a single output. If you want to multi-channel must be customized (large ones, and each current). On the one hand increases the cost, and will have any change would be very troublesome.

 

So in the case of electricity, the best first constant voltage power supply regulator and then using the constant current of multiple constant current module. The greatest advantage that we can get the highest efficiency in a variety of LED street lamps connection structure. Can choose the output voltage of the constant voltage source to achieve the best match. And high flexibility, it is easy to change their combination.

 

As a light source, the dimming is very important. Not only in order to get a more comfortable environment in the home, today, to reduce unnecessary electric light, in order to further the purpose of energy saving is more important. For the led high bay light source dimmer than other fluorescent lamps, energy saving lamps, high pressure sodium and other easy to implement, so it should be in all types of LED street lamps with dimming function.

The plate cooling of the outdoor LED spotlights

 

The plate cooling of the outdoor LED spotlights

 

LED chip is characterized by high heat in a minimal volume. The heat capacity of the LED itself, it must be the fastest heat conduction out, otherwise it will produce a high junction temperature. Heat leads to the chip outside, a lot of improvements in the outdoor LED spotlights chip structure.

 

In order to improve the heat dissipation of the LED chip itself, the most important improvement is the thermal conductivity of the better substrates. Early outdoor LED spotlights only Si silicon as the substrate. Later changed to sapphire as a substrate. The thermal conductivity of the sapphire substrate is not very good (at 100 ° C is about 25W / (mK)), Cree’s silicon carbide silicon substrate in order to improve the cooling of the substrate, its thermal conductivity (490W / (mK), nearly 20 times) than the sapphire. And sapphire silver plastic solid crystal, the thermal conductivity of the silver plastic is also very poor. Silicon carbide only drawback is the cost more expensive. Cree is the production of silicon carbide substrate led high bay lights.

 

Using silicon carbide as a substrate, can indeed greatly improve its heat, but its cost is too high, and patent protection. Recent domestic manufacturers began to use the silicon material as a substrate. Because the base of silicon materials not subject to patent restrictions. And the performance is better than sapphire. The only problem is the expansion coefficient of GaN and silicon that much difference, but prone to cracking, the solution is to add a layer of aluminum nitride (AlN) as a buffer in the middle.

How the junction temperature is produced in SMD high power LED

 

How the junction temperature is produced in SMD high power LED

 

LED heat because the added energy is not completely converted to light, but part of the conversion into heat. SMD high power LED light effect only 100lm / W, its electro-optical conversion efficiency of only about 20 to about 30%. That is about 70% of electrical energy into heat energy.

 

Specifically, the generation of SMD high power LED junction temperature is caused due to two factors.

 

1. The internal quantum efficiency is not high, and is compound when electrons and holes, and cannot be 100% to generate photons, commonly referred to as “leakage current” which PN carrier in the composite rate. Leakage current multiplied by voltage is the power of this part, which is converted into heat, but this is partially accounted for the main component of the internal photon efficiency is close to 90%.

 

2. Internally generated photons cannot be all shot to the external of the chip and the last is converted into heat, this part is the main, currently known as the external quantum efficiency is only about 30%, most were converted to heat.

 

Although the incandescent light efficiency is very low, around only 15lm / W, but it almost all the electrical energy into light energy radiate out, because most of the radiation is infrared, light efficiency is very low, but exempt cooling problems.

 

The most common civilian light is the incandescent lamp, which is our ordinary bulbs. If the SMD high power LED is to replace incandescent bulbs, it is necessary to develop a in terms of the lamp shape or appearance of similar bulbs and incandescent bulbs, which is often referred to as led high bay bulb. Imagine, Bulb market is very huge.

The heat dissipation of household LED bulbs used in the bathroom

 

The heat dissipation of household LED bulbs used in the bathroom

 

LED cooling is now more and more people attach importance to, this is because the household LED bulbs failure or life is direct and to the junction temperature, heat is not good to high junction temperature, short life of the law of temperature in accordance with Porto Vilnius reduce the life of 10 ℃ will be extended 2 times. Released from Cree, Inc. the light fades and the junction temperature diagram (Figure 1) can be seen, the junction temperature can be controlled at 65 ℃, then the light fades to 70% of the life of up to 100,000 hours! This is the life people dream, but really can be achieved? Yes, as long as to seriously deal with it the heat dissipation problem is likely to do! Unfortunately, the actual cooling of the LED lights, a far cry from this requirement! So that the life of the household LED bulbs into the main problems that affect its performance, it is necessary to be taken seriously!

 

To junction temperature of 25 degrees when the light-emitting 100%, then the junction temperature to rise to 60 degrees, only 90% of the amount of light emitted; junction temperature of 100 degrees down to 80%; 140 degrees, only 70%. Seen to improve heat dissipation, it is very important to control the junction temperature.

 

In addition to the heat of the led high bay light will be making its spectral shift; color temperature increased; forward current increases (constant power); reverse current increases; increased thermal stress; phosphor epoxy accelerated aging problems, so that the household LED bulbs heat dissipation is the most important issue in the design of the LED lamps.