Hello,thanks for reading my post first.

I made a power supply which can produce -12V according to the data-sheet of LM2576-12. The outputted voltage is 24V and the 0.5A re-settable fuse has been used. Occasionally I found a circuit board which exists a situation that the re-settable fuse will protect automatically if overflowing. After that, the lagging circuit has been add in. And the lagging time is about 650ms -12output. However,the overflowing still existed.

  The outputted inductive energy storage is 330uH and the outputted capacitance is 440uF. The capacitance in the inputted port is 660uF. Here the freewheel diode is B340A.

  After that, joining in buffer circuit which the capacitance is 5uF. E:\ Can be seen obviously that the building time of -12V is about 650ms from oscilloscope. But I don’t understand why there has a pretty big current shock when powering on.

Here the switch power is big enough that the output is over 10A. When in ballast, it need about 20ms to build a stable voltage from 24v.It can start normally if the switch voltage is stable and the circuit board is closed. The biggest shock current can arrive 20A. But the shock time is so short just about 200us.

Now my main problem is: it can’t enable when in -12V. Why a pretty shock current exist here when starting? How to explain it?

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