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After investigation, the inductors burns out for the following causes:
1.The inductors does not match the output power of the switching power supply. Coil DC resistance is large, resulting in full load or overload output, coil temperature continues to rise until burned. This is possible but unlikely.
2. Power overload operation for a long time (more likely). This will lead to increased coil resistance loss (DC) and eddy current loss (AC) of the inductor, both of which are turned into heat energy, making the temperature of the inductor rise rapidly until it burns out. General switching power supply overload 50% (that is, 150% of the rated output power), the protection circuit comes into play.
The rated output power of the power supply, in fact, is also the limit output power, can not be exceeded when used, and to leave a certain margin. Only in this way can it run continuously, safely and stably.
3.The quality of inductance is wrong. If the quality of the inductor core is not good, when there is a large high-frequency AC component through the inductor, it will produce a large eddy current loss in the magnetic core, so that the temperature of the magnetic core coil will continue to rise until burnt out.
4. The first filter capacitor fails. This will cause all the pulsating AC components after rectification to be added to the inductor, so that the eddy current loss of the magnetic core reaches the maximum, and the inductor will burn out due to the rapid increase in temperature. At this time, the output voltage is reduced and the voltage is increased by negative feedback, which makes the output pulsating AC component larger and the eddy current temperature of the magnetic core rise faster, leading to a vicious cycle and finally the inductance is burned out.
5. Short circuit between turns of inductor coil. This is also a possible reason, similar to a power transformer, if there is a short circuit between turns, the transformer will burn.
