LED fluorescent lamp adopts CREE and AOD super bright LED white light as the light source, and the shell is acrylic / aluminum alloy. LED fluorescent lamp installation is relatively simple. It is divided into two types: built-in power supply and external power supply. When installing the built-in power supply, remove the original fluorescent lamp and replace it with the LED fluorescent lamp, and remove the ballast and starter to allow 220V AC The mains electricity can be directly added to both ends of the LED fluorescent lamp. The external LED fluorescent lamp with power supply is generally equipped with a special lamp holder, which can be used after replacing the original one. At present, almost all the power sources of LED fluorescent lamps on the market are built-in. The so-called built-in means that the power supply can be placed inside the lamp. The biggest advantage of this built-in type is that it can be made to directly replace the existing fluorescent tube without any changes to the original circuit. Therefore, the shape of the built-in power supply is usually made into a long bar shape, so as to be inserted into the semi-circular lamp tube. There are two types of built-in power supplies, one is non-isolated (Figure 1) and the other is isolated (Figure 2).
Non-isolated means that there is a direct connection between the LED load end and the 220V input end, so there is a danger of electric shock when touching the load. The isolation between the 220V and the aluminum shell with only a very thin insulating layer of the aluminum substrate is usually not easy to pass CE and UL certification.
Isolation means that there are isolation transformers at the input and output ends. Such transformers may be of commercial or high frequency. But all can isolate the input and output. The risk of electric shock can be avoided. It is also easy to pass CE or UL certification.
1. Power consumption of built-in power LED fluorescent lamp
The biggest advantage of using the built-in power supply is that it can directly replace the existing fluorescent lamp without any changes to the original wiring. Does this built-in advantage also pay a price? This is true, and the price is not small. This starts with the ballast structure of ordinary fluorescent lamps:
We know that the starting of the most common fluorescent lamp is to use a series iron core inductor and a parallel starter (Figure 3a). For this kind of circuit, when the LED fluorescent lamp is directly replaced, just unplug the starter. However, because the iron core inductor is still connected in series in the circuit, it still brings about 6.4W (Philip) to 10W (domestic) losses. As a result of this additional loss, the power saving efficiency of the LED is greatly reduced. For example, a 20W LED fluorescent lamp can replace a 36W fluorescent lamp. Taking the built-in non-isolated 20W LED fluorescent lamp as an example, the measured results are as follows. ‖
In other words, the result of direct replacement is that the efficiency is greatly reduced. For domestically produced inductive ballasts, the efficiency is only 56.2%. Only 6.8W less power than ordinary fluorescent lamps.
This makes the power-saving efficiency of LED fluorescent lamps greatly reduced, making contract energy management (EMC) difficult to implement.
Second, heat dissipation and life
Another biggest disadvantage of the built-in power supply is its low life. Because the power supply must be placed in an aluminum tube, the aluminum tube cannot be made in the form of fins, but can only be an ordinary semi-cylindrical type, at most with some shallow strip grooves on the surface (Figure 4) .
The surface area of ​​this half-cylinder is: 2πR * h / 2 = πR * h. For the T8 tube, its diameter is 26mm, so the radius is 13mm. The 1.2-meter T8 tube has a surface area of ​​π * 1.3 + 120 = 490cm2. We know that the surface area of ​​LED heat sinks usually requires 60cm2 / W. , So this semi-aluminum tube can only dissipate about 8W of heat. The T8 LED fluorescent lamp usually has an input power of 20W. Assuming that the luminous efficiency of the LED is only 20%, then the input electric power of 16W becomes heat. But now only 8W of heat can be dissipated, and 8W of heat can not be dissipated, the result is that the junction temperature of the LED is increased and the life is shortened.
Not only that, because the power supply is built in, the heat of the power supply is also added to the tube. Assuming that the efficiency of the power supply is 88%, there is also 2.4W of heat to be dissipated, which is equivalent to an increase of 30% of the heat, that is to say a total of There is 10.4W of power that cannot be emitted. This makes the difficulty of heat dissipation of LEDs even more, or makes the service life of LEDs shorter. Moreover, the length of the power supply is about one-fifth of the length of the lamp tube, and the heat generated by the power supply is also concentrated in this section, so that the LEDs near the power supply are more hot baked, so the life is more than the LEDs in other places Short, when the lamp is damaged, the section close to the power supply is blacked out first. It can be considered that the life of the LED fluorescent lamp with built-in power supply will not exceed 10,000 hours.
And put the power supply in the tube, the power supply itself must withstand the high ambient temperature generated by the LED, which greatly reduces the life of the electrolytic capacitor in the power supply, which also reduces the life of the entire lamp.
3. Cost of use
Because the life of the LED fluorescent lamp with built-in power supply is only 10,000 hours, compared with the 50,000 hours of external power supply, its use cost is obviously five times higher. Not only that, in the process of use, whether the LED is damaged or the power supply is damaged, usually both must be discarded together. The LED fluorescent lamp of the external power supply can be damaged and lost.
In addition, the built-in power supply type also increases the cost of recycling electronic waste. Because the power part must be taken out and dealt with separately.
Fourth, other functions
The external power supply not only has high efficiency and long life, but also can add special functions such as manual dimming or automatic dimming, which are unmatched by the built-in type!
From the above introduction, we can conclude that the shortcomings and problems of the built-in type are very serious. Unfortunately, some people just want it to be 10% cheaper at the time of purchase, regardless of its use cost is more than 5 times higher. It can really be said that it is a big loss, not a gain!
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