Possible reasons are as follows:
1, external causes, that is, the output voltage fluctuation and jump caused by the instability of the input voltage of the external power grid.
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2, the internal cause, that is, the internal fluctuation and jump caused by the quality of the related components of the switching power supply.
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3. The unbalanced operation of the load will also cause its voltage fluctuation and jump. This is the disadvantage of switching power supply, it is inevitable. The switching power supply is suitable for the occasion where the load is relatively fixed, and the switching power supply should not be unloaded. Adding a fixed access discharge resistance to maintain a suitable minimum current can reduce this voltage jump, but increase power consumption and reduce efficiency.
If the chip is only 12 ~ 13V, it may not be started, pay attention to measuring whether the pin 8 has 5V output. Either 3844 itself has a problem, or its power supply part of the problem, mainly check these places:
1, 7 pin power supply filter capacitor, including a diode and series resistance.
2, the main filter capacitor.
3, auxiliary power supply winding pin virtual welding.
4, the starting resistance should also be measured.