The disadvantages of the built-in power supply of LED fluorescent lamps and the seriousness of the problem

At present, almost all of the 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 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).

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.

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.

First, the power consumption of the 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:

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.