After entering 2011, LED interior lighting gradually to march, it also means the beginning of march to civilian families. On the one hand this is a big happy event, because the civilian market is very large; on the other hand is a very serious challenge, because the civilian market requirements particularly low cost, reliability is particularly high. Leave now fully meet the requirements of the civil markets are still far, we can say there is a long way to go.
The most common civilian lamp is an incandescent, which is our ordinary use of the light bulb. So if the LED to replace incandescent bulbs, it is necessary to develop a cap in terms of shape or appearance are similar to light bulbs and incandescent bulbs, this is what we often referred to as LED bulb. Imagine, bulb market is enormous.
One. The LED bulb requirements
Because you want to replace incandescent, so at least the following requirements:
1. Brightness To a considerable wattage incandescent usually talk about not talking about the number of lumens. LED although you can also talk about wattage, but because LED light effect is still evolving, but said its wattage and do not represent the number of lumens. The most commonly used incandescent wattage is 15 watts, 30 watts, 45 watts, 60 watts, 75 watts and 100 watts and so on. If you talk about the number of lumens, you can use to calculate the luminous efficiency of incandescent lamps. Luminous efficiency of incandescent lamps in 7.5-12lm / W. The higher the wattage the greater the efficiency. Therefore, the relative number of lumens listed above several wattage incandescent can list as follows:
If using LED to replace, you can draw the appropriate wattage. But because the LED luminous efficiency continued to rise, it is difficult to give exact figures. Currently usually assumed LED1, its luminous efficiency of 100lm / W, if the use of the highest light efficiency LED2, its luminous efficiency of 130lm / W (warm white light effects will be lower than this value). You can draw these two luminous efficiency LED corresponding to the number of watts. However, because the LED requires a constant current source and the constant current source has a certain degree of efficiency, is assumed to be 85%, the other can not be used as a transparent LED bulb, but only the use of white foam shell. Its light transmittance of about 85%. Both equal to 0.72 multiplied. The number of watts after considering the above factors can be drawn and incandescent equivalent to. Seen from the table, LED2 at the same brightness can save about 10 times the power. There is little need of special note. That is, from the current efficiency and heat dissipation LED light bulb is concerned, it is impossible to do 10 watts or more, that is still only can replace 60-75W incandescent LED bulb. Of course, another matter PAR lamps (discussed later).
2. To shape generally similar to pear-shaped incandescent, the LED bulb should also be for the pear-shaped. This is easy to do. But for all glass products incandescent, LED heat dissipation is difficult to adopt because the whole structure of the glass. The following will be discussed in detail the structure of LED bulb.
3. Small size to be quite, because the LED needs constant current source and a heat sink, so it is very difficult to do
The weight to be quite the same because the LED needs constant current source and a heat sink, so it is very difficult to do
5. The lamp must be the same China in the past are mostly used bayonet, most of the reform and opening switch and the United States, like the screw-on. E26 is the US or E27. This also is very easy to do
6. Power to be the same, should be 220VAC (or US 110VAC), this is no problem
· Two. Structure LED bulb
LED bulb can be divided into external and internal structures. We first look at its external structure. A typical LED bulb shape shown in Figure 1 (which is the author of the recent Fry's Electronics store to see in Silicon Valley's largest power LED bulb, price $ 40):
This is one of 5W LED bulb, length 13cm, radiator length 5cm, diameter 4.5cm, blister length 5.2cm, diameter 5.5cm, weight 114 g. It can replace 45W incandescent about. Its external structure mainly includes three parts, one lamp, two radiators, three is a blister. The internal structure are mainly two parts, one constant current drive power, the second is the LED board (including the aluminum plate and LED), including (Figure 2).
The following were constituted to discuss these parts.
III. Bulb power
Bulbs are used as electricity supply, so the power must also be mains AC input, the English called Off-Line, there is the Chinese translation offline is very appropriate, because the English meaning intended From Line should be translated into online, but will be mixed and online network, so it is better to be directly referred to the mains power supply.
· Bulb mains power supply basic indicators are as follows:
1. Power basic types: the main points of isolated and non-isolated two kinds, whether it refers to the load side of the line of fire 220V isolation. Generally speaking, non-isolated because no isolation transformer, so low cost, but requires high pressure aluminum plate, otherwise the radiator is likely to live. So the comparison is not easy to pass safety inspection. Isolated relatively safe, relatively easy to pass safety regulations, but the high cost.
2. Power output: Because of the volume of the size of the bulb incandescent bulb must be considerable, so the limited size of the radiator, there is no more than 9W.
3. Power efficiency: Usually about 80-85% of isolated, non-isolated at around 90%
4. The power factor (PF): 0.5-0.6 without PF correction, plus PF correction at around 0.9-0.99
5. Small size: bulb left power due to space is small, so the volume is very strict limitations.
Here to introduce several typical bulb power.
3.1 Non-Isolated Power
Here is a used by the US Semiconductor NCP1014 non-isolated power supply schematic diagram (Fig. 3)
The basic indicators of the power supply as follows:
Figure 4: NCP1014LEDGT Outline
In fact, this is one of the core power supply constant current diode NSI45025, to ensure that the LED constant current at 25mA. So it can only be used for low-power SMD type LED. NCP1014 integrated circuit in which the applied style is actually an active power factor correction (PFC), it can be raised to the power factor of> 0.9 to meet the US Energy Star requirements. Input of L1, C1, C2 is an anti-electromagnetic interference (EMI) filters. Its disadvantage is non-isolated, so 220V will be directly added to the load on the LED.
· In fact, if you do not require power factor, then the constant current diode (CRD) power scheme can be made very simple (Figure 5).
Figure 5: The easiest constant current diode bulb power supply (Click chart to enlarge)
This power factor is between about 0.5-0.6. Because the circuit is simple, so volume can be made small, and low cost.
3.2 isolated power supply
To improve security, the best use of isolated power, so much an isolation transformer, increasing the size, cost, reduces efficiency. Figure 6 is an adoption of iWatt iW3610 isolated flyback power supply circuit. In fact, this chip and Cypress's CY8CLEDAC02 very similar.
Figure 6: The iW3610 isolated power supply circuit diagram (click chart to enlarge)
The main technical indicators as follows:
This circuit can also automatically detect whether the TRIAC dimmers on the wall, if any, can be dimming, dimming range can be transferred to its 100% from 2%. And finally adopted the PWM dimming, dimming frequencies up to 900Hz, thus avoiding flicker. Also thanks to the quasi-resonant control so that the total efficiency of up to 85%. It is also characterized by the use of a primary feedback transformer thereby eliminating the optocoupler devices. Its shape is shown in Figure 7. Its shape is specially designed for the bulb.
· Four. Bulb radiator
The LED bulb is usually in an aluminum plate welding (LED floor), the piece of aluminum plate again and a circular aluminum heat plate is fixed, then put this piece of aluminum heat sink plate is fixed to the housing up (see Figure 8) .
Figure 8: LED to the heat sink plate is fixed up to
Figure aluminum cooling plate can be seen there finishing marks. After the floor after finishing LED can be directly fixed up, otherwise, there will be an air gap between the two, the need to improve the thermal plastic coated silicon thermal conductivity.
Bulb due to size restrictions so the heat is a big problem. Either the radiator can only rely on convection and radiation are two ways to put heat into the air to go, and the ability to both heat and its heat is proportional to the area. The bulb of the cooling area can be calculated as follows. Assumed the radiator can be approximated as a truncated cone spiers. Assuming that the height of the great circle of the cone is H, diameter D, and the height of the truncated cone of small round h, diameter d.
Figure 9: truncated cone
The lateral area of the cone is πHD / 2, so that after an apex truncated lateral area is πHD / 2-πhd / 2 = π (HD-hd) / 2. Assuming that H = 8cm, h = 3cm, D = 5cm, d = 3cm, then the lateral area of a truncated beyond that 48.7cm2, can be approximated as 50 cm2. And because most of the radiators are open trench to increase its cooling area, open trenches after the increase in the cooling area of the groove depth g multiplied by the length l multiplied by 2, multiplied by the number of grooves. The average depth of the groove is assumed 0.3cm, length 5cm, the number of grooves was 46, then after the opening area of the trench increases 0.3x5x2x46 = 138. Cm2. Total cooling area of 188 cm2. According to the empirical data, the required heat dissipation area per watt at about 35-60 cm2. How Much depends on the specific ambient temperature and allowed to heat up. Because the bulb is used mostly indoors, the ambient temperature is not very high, so you can use 35 cm2 / W. So 188 cm2 cooling area can be scattered by about 5.3W. But this is only a very rough estimate, the concept can be only one order of magnitude. The real situation or to the actual measured heat can.
· Japan's technology online dismantling several LED bulb. And measured its blister temperature, the results shown in the following table: Because temperature is the same, the following table are several housing bulb temperature.
(Click chart to enlarge)
Figure bulb power from 7.5W to 4W. The lowest temperature is 4W bulb, its shell temperature of 38 degrees. The highest temperature for Toshiba Lighting 7.2W bulb, its surface temperature up to 61 degrees. This is because the Toshiba bulb slotted groove radiator no reason. So do not slotted groove radiator, although the surface is smooth, good-looking appearance, but its cooling effect will be a lot worse. While the surface temperature is higher, the thermal resistance in the same system and the power situation, LED chip junction temperature is higher, the shorter the life of the LED.
Due to restrictions bulb radiator area, it is difficult to heat than 7-9W. According to the current LED light effect, it's also equivalent to 60W incandescent lamp lumens. With LED light effect later gradually increased, I believe there will be the same size and can replace 100W incandescent.
Most of the heat sink material aluminum alloy, because of low cost, easy processing and good thermal conductivity. But recently there has been a lot of insulated plastic radiator and ceramic radiator, the cooling effect is not bad. Because the last heat mainly by convection and radiation. The convection is completely determined by its shape and size. Radiation and radioactive material is relevant. Thermal emissivity of various materials in the following table:
(Click chart to enlarge)
Seen from the table, the oxidation treatment is an important way to improve the heat radiation of metal material. The thermal oxidation process does not require any plastic can achieve extremely high radiation coefficient. So long as its shape and a metal heat sink, then the effect of convection and radiation, and effects are the same metal radiator. But its certainly not as good thermal conductivity metal, so the overall cooling effect will be worse. But if it is made as thin as possible, coupled with the inner wall of a layer of metal, you can put this low thermal conductivity to minimize the negative factors. Now has thermal conductivity of greater than 20 w / mk of plastic, but its price is relatively high. The ceramic and plastic radiator radiator the case. But its higher thermal conductivity can be done, of course, but also the cost is much higher. Figure 10 is Shanghai Long-mao Microelectronics 6W plastic bulb. Its heat sink temperature of 67 degrees.
Figure 10: a plastic radiator 6W LED Bulb
The biggest advantage of plastic and ceramic insulation, so even non-isolated power supply is also easy to pass safety inspection.
· In addition, in order to improve heat dissipation constant current drive power of the bubble shell, usually have added thermal sealant to replace the poor thermal conductivity of air. Another method is to punch in the radiator, so that the flow of air. However, there will be a water problem.
Five. Bulb blister
The so-called blister refers to the transparent front of the bulb. In incandescent lamps, the entire housing is made of glass, but in the bulb lamp, although it could be made of glass in front of the housing, there is actually doing. But because LED bulb heavy weight, more than five times better than incandescent light weight, if made of glass, then fall to the ground, mostly on the possibility smashes. So more LED bulb uses made of plastic foam shell to prevent break. And LED bulb because the heat is dissipated from the heat sink, so all through the blister Everbright visible, there is little infrared heat, so the use of plastic blister will not do because of overheating and damage.
However, the biggest problem is the problem of the plastic housing of the light transmittance. Because the LED presence of glare problems, so far as possible milky foam shell, so as not to see the inside of LED lights. The milky white blister. Its transmittance is more problematic. So for the plastic shell for LED bulb light bulb has the following requirements:
1. with high transmittance, high diffusion, no glare, no light;
2. The light source is better concealment (see LED lamp beads as possible);
3. The light transmittance of more than 90%;
4. With a high flame retardancy;
5. With high impact strength;
Now there is a country called Zhiguang LED optical lampshade is said to achieve all of the above requirements (Figure 11).
Figure 11: Various LED plastic blister (Click chart to enlarge)
· If this really can achieve 94% light transmittance, but also anti-glare, no light, then there really is a very ideal. Figure 12 shows the appearance.
Figure 12: Zhiguang LED optical lampshade Appearance
VI. Several brand LED Bulb
The following lists the measured results of several mass-market brand LED bulb
It may be noted a 60W incandescent bulb weighs only 28g. These LED bulbs than about five times lighter. Another light-emitting efficiency is not the table itself, the luminous efficiency of LED, but the luminous efficiency of the bulb, including the power efficiency and the transmittance of the mask. Therefore, to be able to reach 100lm / W luminous efficiency overall is still some way to go.
Seven. LED PAR lamps
PAR lamp is actually a high-power halogen lamp Philips specifications, Philips called it "chloride lights." But the name has not been promoted. Generally known as "Down" or "Spotlight." The spotlight has mainly refers to the kind of MR16 lamp socket, so we have also called PAR lights or downlights. And because of this PAR lamps are compatible, so the high-power LED PAR lamps and PAR lamps will also adopt the same size. But different structures, different wattage and different brightness. Philips PAR20, PAR30 and PAR38 shape as shown in Figure 13. And compatible LED PAR lamp, its dimensions and they are identical (Figure 14).
Figure 13: Philips PAR20, PAR30 and PAR38 shape (click chart to enlarge)
Figure 14: and PAR20, PAR30, PAR38 corresponding LED Downlight (Click chart to enlarge)
· After using the LED, because there is no uniform standard, so having a variety of performance indicators, now select one of the more typical and original Philips halogen indicators compare the following table.
(Click chart to enlarge)
In which both light intensity indicators used different units, Philips uses cd (candlelight), and are usually LED is used lm (lumens). Relationship between the two is as follows: φ (lm) = 4πI (candles). But because the two different solid angle of emission, it is not converted. Only roughly speaking, the luminous efficiency of halogen lamps is about 17-33 lm / W. The LED luminous efficiency 100-130lm / W. About 4-6 times higher than halogen.
Structure PAR lamps and bulb is basically the same, only bigger size, wattage larger. Therefore, the power supply requirements should be larger.
In February this year the company announced a US Sprinter for LED constant current driver IC (LT3799), it can drive 4-100W of the LED, and itself with PFC, the external power MOSFET switch, without the need for isolated flyback optocouplers, minimize external components, but also for SCR dimming.
Flyback isolated constant current power supply can be used for high-power LED PAR lamp (Click chart to enlarge): 15
This diagram is a circuit diagram 24 watt PAR lamp demo board to. The main technical indicators are as follows:
· It's a demo version of layout shown in Figure 16. Of course, the specific application may also be designed into a round.
Figure 16: The demo version of LT3799 (click chart to enlarge)
The mains current source because of power, and can adapt to a wide power range 4-100W, they must be using an external MOS switch, but also because of power, it requires the use of power factor correction (PFC). For different power, in addition to select a different MOS tube, but also asked to choose a different size transformers. Transformer to increase the overall size and weight of the constant current source, reducing efficiency. But it is necessary to isolate the mains.
VIII. Market prospects LED bulb
According to official estimates, LED grow at an annual growth rate of more than 30% growth until 2014. LED bulb if you want to replace all incandescent words, its global market reached $ 640 billion, while until December 2010, LED bulb sales of 20 million. Only 3.2 percent of its market penetration is expected to reach 12.5% in 2013. That is the equivalent of $ 80 billion in sales. And the unit price will be an annual rate of 15-20% descending. One can replace 60W incandescent LED bulb, selling $ 90 in 2008, to 2010 it sold only $ 40.
And China is a big country of production and use of incandescent, 2009 produced 3.79 billion incandescent lamps, about one-third of global production, domestic consumption of 1.4 billion annually. But China has not specified a date when the ban on the production of incandescent lamps, but only through consumption tax preparation to accelerated phase-out incandescent lamps. However, there are only going to use energy-saving lamps to replace incandescent lamps instead of LED bulb to replace. So while China also produced a lot of LED bulb, but mainly for export. Domestic sales account for only a tiny minority. The fundamental problem is too expensive. But with the LED luminous efficiency, lower production costs, LED bulb there will one day be able to replace all incandescent lamps. Replace incandescent assumed the whole of China takes 10 years, we can roughly estimate what this decade in the process of China replace LED bulb.
(Click chart to enlarge)
* As the RMB exchange rate is not good forecast, so in US dollars
Now the highest luminous efficiency LED is about 140lm / W, 2020, LED light effects will be raised to 240lm / W. This can reduce power consumption, reduced size and weight of the heat sink. Thereby reducing the overall cost of LED bulb. At that time, LED bulb completely replace incandescent era will come!
