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240VAC Offline flyback power supply clearances

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treez

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Hi,
Just so we can check a PCB we are buying in, could you please state what is the distance required between the tracks (covered in solder resist) at the output of the 50Hz full bridge rectifier in a 240vac offline flyback smps? They obviosuly have 340Vpk between them...ie its primary side DC positive and DC negative.
 

Hi,

There a lot more than the input voltage that determines the distance.
* the regulations of your country
* which regulation
* where/how the device us used (commercial, industrial, medical..)
* environmemt ( altitude, humidity, dirt...)
* and so on...

Klaus
 

Pollution degree ( per the standards ) is a big determinant, if dry, no moisture, no dust etc, you can get away with 1mm for 230Vac / 350VDCpk - working creepage

however where condensation, dust, etc can have ingress, then for 230Vac, working insultaion 3.4mm creepage, and even this is too light for long term reliability ...
 

Pollution degree ( per the standards ) is a big determinant, if dry, no moisture, no dust etc, you can get away with 1mm for 230Vac / 350VDCpk - working creepage
however where condensation, dust, etc can have ingress, then for 230Vac, working insultaion 3.4mm creepage, and even this is too light for long term reliability ...
Thanks, we sometimes think that if the tracks are covered in solder resist , then the solder resist should provide the insulation..?....or do we need to conformal coat?
No dust ingress's to our enclosure innards, and we have rubber seals to keep water out.
 

We think that surely the solder resist isnt going to degrade with time?
 

Hi,

Solder resist is considered as "no isolation", afaik.

Most pribably because it will widely depend on
* type: lacqueur, foil
* thickness
* production process

Especially the thickness will be problematic to control reliably. On every edge of the traces the thickness will vary a lot with lacqueur viscosity and ammount of lacqueur.

If you want increased isolation you need extra isolation foil or potting compound..

I recommend to read through the corresponding regulations.

Klaus
 

Only"special" solder resist counts... track edges are a problem...
 
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