I'm designing a PCB and I want to use this AC/DC power supply converter. I have found this commercial PCB where they use it and I have these questions:

  1. I have seen that the PCB has some slots (see image) but I do not know if they are necessary due to the AC/DC converter or the relay (to isolate the signal switched by the relay from the rest of the PCB signals). In case they are necessary for the regulator, is it possible to do it with Proteus ARES?
  2. In the datasheet (page 2 of the PDF, labelled "PA-3"), an external MOV varistor is required for 230VAC operation but, with what AC voltage rating? Would it be correct to use a TVS diode?
  3. I have also seen that a TVS diode is added to the PCB at the 5 V output, is it really necessary?

EDIT: I added the schematics and the layout

Thanks in advance.

enter image description here


1 Answer 1


You haven't provided a schematic, so we don't know what is connected to those traces. However, this certainly has the look of increasing the creepage distance to minimize leakage across some isolation barrier.

Circuit boards are made from insulating material. But, stuff happens, and after some use, dust and dirt can get on the PCB. Add some humidity in the air, and you can have resistance orders of magnitude lower between two points than would be if the board were clean.

In some applications, like patient-touching medical devices, a few µA of leakage you can usually ignore become significant. One way to reduce the leakage current despite inevitable dirt and moisture is by increasing the creepage distance. That's the shortest distance along the surface of any object between two conductors. Cutting a slot in a PCB can greatly increase the creepage distance between two critical nets.

Cutting slots in a PCB is a extra step in manufacturing, but is usually cheaper and more desirable than making the device larger.

  • \$\begingroup\$ Thanks for your answer. I found the schematics and the layout, sorry for not adding it before. I have edited adding this information. One question, is the 5 V TVS diode necessary? \$\endgroup\$
    – FranMartin
    Dec 26, 2017 at 14:15

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