zappedagain
Electrical
- Jul 19, 2005
- 1,074
Sorry for the dual post - this wasn't getting any responses in the other group so I'm reposting here...
I'm designing a circuit to meet the CE mark test of 8KV discharge. I read through thread797-134233: calculating minimum air gap and saw a discrepancy that I'm looking to answer.
The dielectric breakdown of air is 3KV/mm, or about 76KV/inch.
I believe I have a copy of the 'Sparkgap breakdown voltages for needle gap' referenced in that thread (I'm not sure because I received it from a colleague in the mid-90s). This table shows a breakdown voltage of about 26KV/in at 25C, 29.9 In Hg baromteric pressure.
That's almost a 3:1 discrepancy between the two techniques. While the chart is more real-world, that seems a rather large safety factor. Are there some other facts that explain the difference between the two techniques? For example, the chart shows that at -40C and 60 In Hg you need to apply a correction factor of 2.30 so that almost accounts for it; those aren't typical operating conditions though.
What I really want to know is: How far do I need to keep my traces from the aluminum enclosure (that is perpendicular to the PCB) to not have the an ESD event jump onto my PCB traces?
I'm designing a circuit to meet the CE mark test of 8KV discharge. I read through thread797-134233: calculating minimum air gap and saw a discrepancy that I'm looking to answer.
The dielectric breakdown of air is 3KV/mm, or about 76KV/inch.
I believe I have a copy of the 'Sparkgap breakdown voltages for needle gap' referenced in that thread (I'm not sure because I received it from a colleague in the mid-90s). This table shows a breakdown voltage of about 26KV/in at 25C, 29.9 In Hg baromteric pressure.
That's almost a 3:1 discrepancy between the two techniques. While the chart is more real-world, that seems a rather large safety factor. Are there some other facts that explain the difference between the two techniques? For example, the chart shows that at -40C and 60 In Hg you need to apply a correction factor of 2.30 so that almost accounts for it; those aren't typical operating conditions though.
What I really want to know is: How far do I need to keep my traces from the aluminum enclosure (that is perpendicular to the PCB) to not have the an ESD event jump onto my PCB traces?
