I often hear people in the industry complain that every time the LED lamp is broken and the power supply is broken, the most unreliable LED lamp is the power supply. Maybe he is telling the truth. However, it is also necessary to analyze in depth the cause of the LED power supply damage.
Recently, the LED lamps in my home have also broken down. When I take it down, it turns out that the power supply is broken, but although this is the case, it should be carefully analyzed.
First look at its photo of the shape:
Although it is just a very simple outline drawing, many problems can be seen, and these problems are common problems of all low-reliability power supplies.
1. Use cheap low-quality components.
We can see that its rectifier bridge (left side in the figure) consists of four rectifier diodes instead of an integrated rectifier bridge. We know that the cost of four diodes is much lower than that of an integrated rectifier bridge, because there are many companies that can produce diodes, because the production of diodes can be done with some of the simplest semiconductor production equipment that has been eliminated in the past, and that can be produced. There are not many companies that integrate rectifier bridges, because they must have high-quality integrated circuit production equipment and raw materials, which can be produced by some large manufacturers, and the price is certainly much more expensive than the four diodes. In fact, high back pressure diodes are not easy to do, and general manufacturers do not necessarily produce highly reliable high-pressure diodes. Later, I measured it with a multimeter, and I found out that there is a rectifier diode that is broken, and the electrolytic capacitor is still good.
So is there no problem with the integrated rectifier bridge? This is not the case. There are also many cases where electrolytic capacitors are broken down without protection. In addition, when selecting the voltage resistance, power consumption and other indicators of components, it is also necessary to leave room for it, such as the withstand voltage of electrolytic capacitors. Although the rated voltage is only 220Vx1.4=308V at the rated 220V, my piece The electrolytic capacitor withstand voltage on the power board is 400V, which should be enough, but we usually use 450V withstand voltage electrolytic capacitor, so the insurance factor can be larger.
2. No protective components are used
As can be seen from the photo, this power supply is not equipped with any protection device. However, as a power source connected to the mains, it is necessary to add protective components. That is because there are various surge voltages on the power grid. It may be a lightning strike at a long distance or a high-power device on the power grid. High voltage pulses caused by switching. If you do not protect this high voltage pulse, it is easy to break through the electrolytic capacitor.
Protection device for LED lamp power supply
The function of the LED power protection device mainly has two aspects. On the one hand, it protects the power supply itself from being damaged by external influences. On the other hand, it protects the external circuit environment from external circuits due to the operation or damage of the LED luminaire.
The main protection devices are as follows:
Varistor
The varistor is used to protect the LED lamp itself. It can be said that regardless of the power source, switching power supply, and linear power supply used in the LED lamp, this protection is required. It is used to protect the surge voltage that often occurs on the mains network. The so-called surge voltage is mainly caused by short-time high-voltage pulses caused by lightning strikes or high-power electrical equipment starting and stopping. Among them, lightning strikes are the main reason. Lightning strikes can be divided into direct lightning strikes and indirect lightning strikes. Direct lightning strikes refer to direct lightning strikes on the power supply network. This possibility is rare, and most large-scale power supply grid systems have lightning protection measures. Indirect lightning strikes refer to surges that are transmitted by lightning-induced electricity on the grid. This surge is highly probable because 1800 thunderstorms occur every moment in the world, with 600 lightning strikes per second. Each lightning strike induces a surge voltage on the nearby grid. The width of a surge pulse is usually only a few microseconds or less, and the amplitude of the pulse can be as high as several thousand volts. Mainly because of its high amplitude, it has the greatest impact on the damage of electronic equipment. If you don't protect it, all kinds of electronic equipment can easily be damaged. Fortunately, the protection of the surge is very simple, just add a surge-proof varistor, usually it is connected in parallel before the rectifier.
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