The fatal defect of LED lamps - surge voltage
Surge voltage seriously affects the service life of LED lamps, such as doing a project, hundreds of desk lamps, often for no reason damage, common like a street installed LED street lights, from time to time, often broken, broken and repaired. There are LED fluorescent lamps, many of which use non-isolated power supply, and they are often found to have blown out during mass production. The root cause is all here. All are caused by surge voltage, common is outdoor lightning strike, or large load on, off, voltage clutter and so on. In writing, a very high voltage is applied instantaneously to the input power source and then transmitted from the input power source to the output.
All LED lamps and lanterns will be affected by the surge voltage hazard, the surge voltage value is different according to the actual situation, and the surge hazard of LED lamps and lanterns, part of the LED drive power supply to solve, such as the surge protection ability of some LED drive power supply voltage 4KV, some lower, some higher.
Switch power supply of PWM adjustment need several clock cycle, and if the input voltage instantaneous change, and time is very short, and there is no time to adjust when switching power supply, at this moment is the moment of the performance of high voltage transmission to the output side, especially now LED fluorescent lamp with step-down circuit, because the load is in 300 v high voltage in the circuit, The 300V high voltage is suddenly increased, and this high voltage moment is added to the output end. In this case, it is easy to damage the power supply.
Some people say that the TVS, the choke, the X capacitor, it's actually not very useful. This is because LEDs operating at normal current currents are sensitive to voltage changes. As we know, the LED work in stable current, such as straw hat lamp, its both ends when increasing the applied voltage of 0.1 V, at both ends of the electric current and not add a few percent, but may increase percent dozens, increased by 0.5 V, nor increase percent dozens, but increase the percentage hundred, or several times, although the above that a few components, there are more than 400 V, This voltage will still make the output current surge, then the output is equivalent to a short circuit, or even the switch tube, directly lead to the annihilation of the LED, the isolation of power supply phenomenon is the explosion of the switch tube, this is the root cause. This is determined by the LED characteristics.
A lot of constant voltage power supply, such as 12V ordinary constant voltage power supply, with some other load, but the same power supply, used for three in a string, often found a lot of fried, the reason is here, because of the load characteristics of LED, it is more likely to damage itself and damage the power supply.