Performance, power supply structure and service li

Performance, power supply, structure and service life of LED fluorescent lamp

recently, LED fluorescent lamp has become one of the first LED lamps to enter the room, because it has many advantages over fluorescent lamp

I Advantages

compared with fluorescent lamps, LED fluorescent lamps have 10 advantages:

1. High luminous efficiency: the luminous efficiency of fluorescent lamps is about lm/w (the luminous efficiency of Philips T8 fluorescent lamps is 72lm/w), while the luminous efficiency of LEDs is more than 100 LM/W. recently, the luminous efficiency of Cree's xlampxp-g has reached 130 lumens/w, and will continue to improve in the future. The difference between the two has now nearly doubled. In the future, it may reach more than three times

2. high efficiency of lamps and lanterns: the efficiency of lamps and lanterns mainly refers to the effective light effect, because fluorescent lamps emit light at 360 degrees, and the light emitted in the opposite direction is useless. Therefore, fluorescent lamps usually use a white lampshade, which can reflect a considerable part of the reverse light. Generally speaking, the efficiency of fluorescent lamps is only about 70%. The LED fluorescent lamp is 120 degrees luminous, so all the light is effective light. Although sometimes I feel that the 120 degree luminous angle is a little narrower, it is still enough in most cases. And this luminous angle can also be adjusted according to needs

as mentioned earlier, the luminous efficiency of Philips T8 fluorescent lamp is 72lm/w, and the 36W fluorescent lamp emits 2592 lumens in total, but the lamp efficiency is only 70%, so the effective lumen number is 1814.4 lumens, and the luminous efficiency of LED has exceeded 130lm/w. Assuming 100lm/w, it can reach 1800 lumens as long as 18W, that is, as long as half the power of fluorescent lamp can have the same brightness

and the luminous efficiency of LED is increasing year by year

3. high power efficiency: because all lamps except incandescent lamps need special power supply, the efficiency of the power supply also affects the efficiency of the whole lamp

take the 36wt8 fluorescent lamp of Philips company as an example. Its rated output power is 36W, but due to the connection of inductive ballast, the measured input power is 42.4w, that is, the core inductance loss is 6.4w, and the efficiency is reduced to 85%. The power consumption of most domestic core inductors is more than 10W, and the power factor is less than 0.512. The power efficiency of LED is usually as high as 90%, and an 18W LED fluorescent lamp only needs 20W input power. The power factor can also reach more than 0.9

compared with fluorescent lamps, it can save more than half of the electricity, that is, using an 18 watt LED fluorescent lamp can replace a 36 watt fluorescent lamp

not only that, LED fluorescent lamp has many other advantages:

4. Long life: the life of a carefully designed LED fluorescent lamp can reach 50000 hours. The life span of a fluorescent lamp is usually only 5000 hours (some domestic fluorescent lamps have a life span of only 300 hours). The difference between the two is nearly 10 times. The best long-life fluorescent lamp has only 10000 hours, and the difference between the two is five times

5. No mercury, no pollution. We know that fluorescent lamps contain mercury. 36mm fluorescent lamp contains mg of mercury, and 26mm (T8) contains 20mg of mercury. Fluorescent lamps use fragile glass as the shell. Once the glass is broken, the mercury in it will evaporate into the air immediately, which can instantly make the mercury concentration in the surrounding air reach mg/m3, times higher than the national regulations. Mercury is a toxic substance that is very harmful to human body. When the mercury vapor reaches 0.04 to 3 mg, people will be chronically poisoned within 2 to 3 months. When it reaches 1.2 to 8.5 mg, it will induce acute mercury poisoning. If the amount reaches 20 mg, it will directly lead to animal death. 1mg of mercury is enough to pollute 5454.5 kg of drinking water, making it below the drinking standard. The LED fluorescent lamp does not contain any toxic substances, which is a completely green and pollution-free light source

6. The color temperature range is wide, which can provide almost any color temperature, and can also provide red, green, blue and even any color of light

7. The color rendering index is high. The color rendering index of incandescent lamp is 95, that of fluorescent lamp is, and that of LED fluorescent lamp is>80

8. no ultraviolet radiation

9. non glass products, not easy to be damaged, resistant to impact and vibration

10. The LED fluorescent lamp with external isolated power supply can't contact the high voltage of the mains at both ends of the lamp tube, only the DC safety voltage lower than 36V, there is no danger of electric shock, and it is a safe lamp

II. Price

at present, the only disadvantage of LED fluorescent lamps is their high price

however, although the current price of LED fluorescent lamps is about ten times that of fluorescent lamps, it is still cost-effective in terms of its service life, power saving and pollution-free. Because if compared with the fluorescent lamp with a service life of 5000 hours, the LED fluorescent lamp with a service life of 50000 hours is already worth 10 times the price, and the electricity saved during this period is completely pure income. In Japan, because fluorescent lamps contain mercury, broken fluorescent lamps have to pay the same amount of money as buying a new fluorescent lamp as toxic substance treatment fees. Therefore, even if long-life (10000 hours) fluorescent lamps are used in Japan, the money paid is equivalent to 10 times the cost of LED fluorescent lamps

in some 24-hour continuous work sites, such as underground parking lots, 24-hour overtime production factories and other places. Saving electricity is also very important. As mentioned above, a T8 LED fluorescent lamp can save about 20 watts of electricity, and 20x365x24/1000=175.2 kwh of electricity can be saved in a year. If calculated at 0.7 yuan per kilowatt hour, 122.64 yuan of electricity can be saved in one year, and the cost of this LED fluorescent lamp can be saved in two years. The electricity saved in the future will become net income

so now there is a practice called EMC (energy management contract) abroad

is funded by a consortium or bank. Install LED fluorescent lights for an underground parking lot or shopping mall for free, but charge the owner all the saved electricity charges. The agreement may be valid for 5 years. After only two years, all the investment can be recovered. From the third year, all the saved electricity bills will become net income. This is a very beneficial investment project. Domestic people have begun to do so

moreover, according to haitz's law, the price of LED will be reduced ten times every ten years

III. led

in order to obtain relatively uniform light emission and disperse heat, LED fluorescent lamps are usually composed of many low-power led beads in series and parallel. There are two kinds of low-power led, one is pin type, commonly known as straw hat tube, and the other is patch type. In the early days, straw hat tubes were mostly used for LED fluorescent lamps, but because of the large thermal resistance (up to 450 ° c/w) and serious light failure, this kind of pin LED has been rarely used by people now, and most of them use patch type. The main indicators of various LEDs are luminous efficiency. Low power LEDs are usually directly expressed in lumens, lifetime (usually expressed in terms of junction temperature), and thermal resistance RJS

the indicators of several commonly used patch LED are as follows:

figure 3020 (a) heat dissipation and 3014 (b) bottom plate heat dissipation mechanism

because 3020 only has two ends of electrode welding heat dissipation, while 3014 adopts bottom plate heat dissipation, the difference in thermal resistance between the two is more than 3 times, and the difference in service life between the two is more than 2 times. 3014 works at 30mA, so its luminescence is also as high as 9 lumens. The luminous efficiency is equivalent to 90 lm/w

the number of LEDs used in fluorescent lamps is usually more than 200. Obviously, it is impossible to connect them all in series, but they must be connected in series and in parallel

generally speaking, it is hoped that there are fewer strings and more strings. In this way, once an LED in a string is open circuit, it will only make this string unlit, and the current of this string will be shared among the remaining circuits. For example, if a total of 200 LEDs are connected into 8 strings and 25 parallel, each string is 30mA, and the total current of 25 strings is 750ma, one string is broken, and the current of each string is only increased by 1.25ma. Conversely, if it is connected into 25 strings and 8 parallels, each string is 30mA, and the total current of 8 strings is 240mA. If one string is open, 30mA will be divided into the remaining 7 circuits, and each circuit will increase by 4.28ma on average

however, some LEDs are protected by a parallel zener diode. Even if there is an open led, this string will not be off, but only this led is off. The above problems do not exist

in addition, if the number of LEDs in series is less than 10, then the power supply voltage required is lower than 35V, which is also lower than the international safety voltage

the number of series and parallel is also related to the possibility of power supply. This will be discussed in the next section

IV. power supply

led fluorescent lamp power supply is divided into built-in type and external type. The so-called built-in type means that the power supply can be placed inside the lamp tube. The biggest advantage of this built-in type is that it can directly replace the existing fluorescent tubes without any changes. Therefore, the built-in shapes are made into long strips, so that they can be stuffed into semi-circular tubes

next, we will introduce two built-in types, non isolated and isolated

1. non isolated constant current power supply: non isolated means that there is a direct connection between the load end and the input end, so touching the load has the risk of electric shock

at present, the non isolated direct step-down power supply is used most. That is, after rectifying the AC to obtain the DC high voltage, the buck circuit is directly used for voltage reduction and constant current control. Its electrical schematic diagram is shown in the following figure:

Figure 1 The main technical features of this non isolated power supply: a wide voltage input range from 18V to 450V, constant current output; Frequency jitter is used to reduce electromagnetic interference, and random sources are used to modulate the oscillation frequency, which can expand the audio energy spectrum. The expanded energy spectrum can effectively reduce the in band electromagnetic interference and reduce the difficulty of system level design; Linear and PWM dimming can be used to support the driving application of hundreds of 0.06w LEDs. The working frequency is 25khz-300khz, which can be set by external resistance

the advantages of non isolated constant current source are simple and high index. Its output current can be determined by the number of LEDs in series and parallel. But in most cases, its output current should not be too large, and the output voltage should not be too high. For example, 264 low-power LEDs are connected into 22 series, 12 series and parallel, each 20mA, a total of 240mA. The volume can also be made very small, usually in long strips, so that it can be put into T10 or T8 tubes. If the current of each string is 30mA, 12 is 360mA. It cannot be realized in some non isolated power supplies. In order to keep the total current of 240mA unchanged, it can only be changed into 8 series and parallel. However, if the total number of LEDs remains unchanged, the number of LEDs in series is required to be increased to 33. At this time, the total voltage will increase to 108.9v. But usually, the maximum allowable output voltage of this non isolated constant current source is 80V. Only the original 22 strings can be maintained, so the total number of LEDs can only be 176. Even if 30mA is used, the total lumens may not meet the requirements

Figure 2 The shape photo of non isolated step-down constant current source

usually its efficiency is about% and the power factor is about 0 92

however, this non isolated power supply also has some limitations, because the non isolated power supply will introduce the high voltage of the AC power supply to the load end, resulting in the risk of electric shock. Usually, the insulation between LED and aluminum radiator depends on aluminum