The fatal flaw of LED lamps - surge voltage

All LED lamps have this fatal flaw, and so far, no one has proposed a good solution. All those who work on LED power supplies or finished LED lamps avoid talking about this problem and pretend not to know about it. However, in actual mass production, this problem is endless. Of course, there are even more people who don’t know much and have no idea what’s going on.

Description of the phenomenon: The most common problem is that when doing a project, hundreds of lamps often break down for no reason. It is common for LED street lamps installed on a street to not light up from time to time, often break down, and then be repaired. There are also LED fluorescent lamps, many of which use non-isolated power supplies. They are often found to be blown up during mass production. The root cause is here. They are all caused by surge voltages. The most common ones are outdoor lightning strikes, or large loads turning on and off, voltage noise, etc. According to the written statement, it is a very high voltage that is instantly added to the input power supply end, and then transferred from the input power supply end to the output end.

We know that the PWM adjustment of the switching power supply requires several clock cycles. If the input voltage changes instantly and the time is very short (, the switching power supply has no time to adjust at all. At this time, the performance is that the high voltage is instantly transmitted to the output end, especially the step-down circuit used in LED fluorescent lamps now, because the load is connected in series in the 300V high-voltage circuit, the 300V high voltage increases instantly, and this high voltage is instantly added to the output end. Isolated power supplies will be better, but many of them can't escape the bad luck.

Some people say that TVS, chokes, and X capacitors are not very useful. This is because LEDs working under normal current are very sensitive to voltage changes. We know that when LEDs work under stable current, such as straw hat lamps, when the voltage applied to both ends increases by 0.1V, the current at both ends does not increase by a few percent, but may increase by tens of percent. When the voltage increases by 0.5V, it does not increase by tens of percent, but by hundreds of percent, that is, several times. Although the above components are still above 400V, this voltage will still increase the current at the output end sharply. At this time, the output is equivalent to a short circuit, or even a switch tube, which directly leads to the annihilation of the LED. The phenomenon of isolating the power supply is to blow up the switch tube, which is the fundamental reason. This is determined by the characteristics of LEDs.

Many constant voltage power supplies, like ordinary 12V constant voltage power supplies, when carrying some other loads, but the same power supply is used in a string of three, it is often found that many of them are blown up. The reason is here, because of the load characteristics of LEDs, it is more likely to damage itself and the power supply.