Author Topic: Isolation between logic and high voltage traces and grounds  (Read 1827 times)

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Offline Pack34

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Isolation between logic and high voltage traces and grounds
« on: September 03, 2015, 10:10:07 pm »
I have some 150V traces on a circuit board that's being controlled with 5V logic and op-amps. For the higher voltage lines, I have the ground piped through the boost converter so I have a controlled path for the return current. I wanted to keep everything as low noise as possible and felt that the return for something like this going under my analog circuitry would be bad news. They both share a common ground, but that just doesn't meet until the input (star configuration). I also wanted to isolate the switching boost converter as much as possible.

How much isolation is enough? We're talking about <1mA of current and I've setup a solid 15mil isolation but I just wanted to be that it's enough before I had it made. This is the first time I'm working with voltage this high and wanted to be sure to keep noise to a minimum.

Any advice?
 

Offline fivefish

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Re: Isolation between logic and high voltage traces and grounds
« Reply #1 on: September 03, 2015, 10:27:41 pm »
Why not use an optocoupler?

 

Offline Chris C

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Re: Isolation between logic and high voltage traces and grounds
« Reply #2 on: September 04, 2015, 01:14:14 am »
In terms of preventing arc-over, here's an article on the topic, which also provides a handy calculator:

http://www.smps.us/pcbtracespacing.html

For 150V peak, a bare metal trace requires 24 mils clearance.  If coated (solder resist), 16 mils.  If there are any holes in the solder resist, use the higher number near those holes.

If AC line powered, consider if a spike might drive your peak voltage higher, and adjust as needed.  A MOV might be a good idea to limit the possible peak voltage.
 

Offline Pack34

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Re: Isolation between logic and high voltage traces and grounds
« Reply #3 on: September 04, 2015, 01:48:22 pm »
In terms of preventing arc-over, here's an article on the topic, which also provides a handy calculator:

http://www.smps.us/pcbtracespacing.html

For 150V peak, a bare metal trace requires 24 mils clearance.  If coated (solder resist), 16 mils.  If there are any holes in the solder resist, use the higher number near those holes.

If AC line powered, consider if a spike might drive your peak voltage higher, and adjust as needed.  A MOV might be a good idea to limit the possible peak voltage.

That is precisely what I was looking for! Thanks Chris!
 


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