All led luminaires have this fatal flaw, and so far no one has come up with a good solution.
All engaged in LED power supply or engaged in LED finished lamps, have shied away from this problem, pretending not to know, but the actual mass production, this problem is endless, of course, there are more people who do not understand, completely do not understand what is going on. The most common problem is to do a project, hundreds of table lamps, often unprovoked damage, common like a street installed LED street lights, from time to time not bright, often bad, repaired and bad, broken and then repaired. There are led fluorescent lamps, many with non-isolated power supplies, mass production often found to have blown out, the root cause is here. are caused by surge voltages, surge voltages are produced for a number of reasons, common is outdoor lightning strikes, or large load opening, shutdown, voltage clutter and so on.
In writing, it is a high voltage that often reaches thousands of volts, instantly added to the input power supply, and then transferred from the input power end to the output. We know that the PWM adjustment of the switching power supply requires several clock cycles, and if the input voltage changes instantly (up to thousands of volts), and the time is short (dozens of, hundreds of MS), then the switching power supply simply does not have time to adjust, then the performance is the instantaneous high voltage conduction to the output end, Especially now LED fluorescent lamp with the buck circuit, because the load is strung in the 300V high-voltage circuit, 300V high pressure instantly become larger, this high pressure instantly added to the output.
Isolated power supplies will be better, but many are also difficult to escape bad luck. Some people say that using TVs, chokes, x capacitors, in fact, is not very useful. Because LEDs that work under normal currents are sensitive to voltage changes. We know that LEDs work at stable currents, such as straw hat lamps, when working at 20MA, stable voltages at 3. At around 1V, the voltage added at both ends increases by 0. At 1V, the current at both ends is not an increase of a few percent, but may increase the percent, increasing by 0. 5V, is not to increase the percent, but to increase the percent, that is, several times, although the above few components, can play a little role, but after the TVs filtered voltage, or more than 400V, this voltage will still let the output end of the current sharp increase, then the output is equivalent to short circuit, Non-isolated power supply performance is an instant blow of constant current ring, and even switch tube, directly lead to the LED completely destroyed, the phenomenon of isolating the power supply is to blow up the switch tube, resulting in the lamp is not lit, this is the root cause.
This is determined by the LED characteristics.
A lot of constant voltage power supply, like 12V ordinary constant voltage power supply, in the belt of some other loads, often found that the damage rate is very low, but the same power supply, used for three a string, several strings and point led, often found a lot of bad, the reason is here, because of the LED load characteristics, it is more likely to damage their