Mao Yuhai: Problems and shortcomings of the built-in LED fluorescent lamp

At present, almost all LED fluorescent lamps on the market are powered by 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 used to directly replace existing fluorescent tubes without any modification to the original circuit. Therefore, the shape of the built-in power supply is usually made into a strip shape so as to be inserted into a semicircular tube. There are two types of built-in power supplies, one is non-isolated (Figure 1) and the other is isolated (Figure 2).

LED fluorescent lamp driver

Figure 1. Non-isolated LED fluorescent lamp power supply

Non-isolated means that there is a direct connection between the LED load terminal and the 220V input terminal, so there is a danger of electric shock due to the touch load. There is only a very thin insulation layer of the aluminum substrate between the 220V and the aluminum case, which is usually not easily CE and UL certified.

LED fluorescent lamp driver

Figure 2. Isolated LED Tube Light Power Supply

Isolated means that there is isolation transformer isolation at the input and output. This transformer may be either power frequency or high frequency. But both can isolate the input and output. You can avoid the risk of electric shock. It is also easy to pass CE or UL certification.

one. Power consumption of built-in power LED fluorescent lamp

The biggest advantage of using a built-in power supply is that it can directly replace existing fluorescent lamps without any changes to the original wiring. So is this built-in advantage also cost a certain price? This is true, and the price is not small. This starts with the ballast structure of ordinary fluorescent lamps:

LED fluorescent lamp driver

(b) Electronic ballast

Figure 3. Fluorescent lamp power supply circuit diagram

We know that the most common fluorescent lamps use a series of core inductors and a parallel starter (Figure 3a). For such a circuit to be directly replaced with an LED fluorescent lamp, it is only necessary to remove the starter. However, since the core inductor is still connected in series in the circuit, it still brings losses of nearly 6.4W (Philip) to 10W (domestic), and as a result, the additional loss of this part greatly reduces the power saving effect of the LED. For example, a 20W LED fluorescent lamp can replace a 36W fluorescent lamp, and the built-in non-isolated 20W LED fluorescent lamp is taken as an example. The measured results are as follows.

That is to say, the result of direct replacement is that the efficiency is greatly reduced. For domestic magnetic ballasts, the efficiency is only 56.2%. It only saves 6.8W more than ordinary fluorescent lamps.

This makes the energy saving performance of LED fluorescent lamps greatly reduced, so that contract energy management (EMC) is difficult to implement.

two. Heat dissipation and life

Another major drawback of the built-in power supply is its low lifetime. Because the power supply must be placed in an aluminum tube, the aluminum tube cannot be made into the form of fins, but only the ordinary semi-cylindrical type, and at the very least, some very shallow strip grooves are added to the surface (Fig. 4). ,

LED fluorescent lamp driver

Figure 4: Semi-plastic semi-aluminum LED fluorescent tube with hollow aluminum tube

The surface area of ​​such a semi-cylindrical is: 2πR*h/2=πR*h. For the T8 tube, its diameter is 26mm, so the radius is 13mm. T8 lamp 1.2 m, a surface area of: π * 1.3 + 120 = 490cm2 , we know that the surface area of the radiator LED generally requires 60cm2 / W. Therefore, this semi-aluminum tube can only dissipate about 8W of heat. The T8 type LED fluorescent lamp usually has an input power of 20W. Assuming that the luminous efficiency of the LED is only 20%, then 16W of input electric power becomes heat. Now only 8W of heat can be dissipated, and 8W of heat can't be dissipated. The result is that the junction temperature of the LED rises and the life is shortened.

Not only that, because the power supply is built in, the heat of the power supply is added to the tube. Assume that the efficiency of the power supply is 88%, so 2.4W of heat is also dissipated, which is equivalent to adding 30% of heat. There is a power of 10.4W that cannot be dissipated. This makes it difficult to increase the heat dissipation of the LED, or to make the life of the LED shorter. Moreover, the length of the power supply is about one-fifth of the length of the lamp, and the heat generated by the power supply is concentrated in this section, so that the LEDs close to the power supply are subjected to hotter baking, and thus the life is more than that of LEDs elsewhere. 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.

Moreover, the power supply is placed in the tube, and the power supply itself is subjected to the high ambient temperature generated by the LED, which greatly reduces the life of the electrolytic capacitor in the power supply, thereby reducing the life of the entire lamp.

three. The cost

Because the built-in power LED fluorescent lamp has a lifetime of only 10,000 hours, compared with 50,000 hours of external power supply, the cost of use 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 broken which one is lost.

In addition, the built-in power supply also increases the cost of recycling electronic waste. Because the power supply must be removed and processed separately.

four. 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 auto dimming, which are unmatched by the built-in type!

in conclusion

It can be argued that the built-in shortcomings and problems are very serious. Unfortunately, some people just plead that it may be 10% cheaper at the time of purchase, regardless of the cost of using it more than five times. It can be said that it is a small loss, not worth the candle!

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