Power Supply Teardown question

[zerobrain]

Hi,

i have take apart a power supply and came accross a construction Dave showed as well in one of his teardowns (see attached image).

In the image you see lines L1 and L2 entering from the bottom, passing a fuse and an NTC. Then there seems to be an emc filter. But what i don´t get are the spark gaps being "parallel" to the current compensated inductors. Has anybody got a clue what they are being used for in this case?

Not drawn in the picture: after the inductors a four-way- rectifier is applied...

Thanks a lot..

[Jebnor]

With inductors, sudden stopping of current will induce a voltage spike. The spark gaps are there to kill any voltage spike before it gets too bad.  I think.

[Seekonk]

Spark gap?  Are you talking about the cut gap in the board?   The UL clearance for air is less than for just a circuit board.  Notice the other side of the inductor the clearance is much wider and therefore acceptable for that voltage.   Without the cut in the board it wouldn't have passed certification.   That cut is not intended to be a spark gap.

[Niklas]

With inductors, sudden stopping of current will induce a voltage spike. The spark gaps are there to kill any voltage spike before it gets too bad.  I think.

Similar issue, but for CAN bus. Energized inductor with one end fixed to DC, either through a short or a capacitor, creates a voltage transient.
www.ti.com/lit/an/slla271/slla271.pdf

[zerobrain]

Thanks for all the answers!
@Niklas, Jebnor - that makes sense!
@Seekonk - no i really meant the "spiky" things parallel to the coils.

Your explanations made sense, but i won´t get still - after looking more deeply into the schematic: Why the the minimum distances not more an issue after the foru-way-rectivifer? I painted in the diodes forming that rectifier and i noticed (marked yellow) the minimum distance between Vmax and 0 is rather small.

Is that an error or are the rules different here?

thanks very much

Dominik