Electronics > Beginners

What does this symbol represent?

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james_s:
I'm certainly not an expert on this matter, but from what I remembered, ESD pulses can have extremely fast rise times that are difficult to clamp with solid state devices, but a spark gap should in theory be very fast. Static electricity can certainly reach potentials that will fire a spark gap, I mean I've had it zap from my finger to an object almost an inch away. So maybe there is some value in having both depending on circumstances? I can at least understand why an engineer thought there might be value.

T3sl4co1l:
Thyristor devices aren't fast enough for ESD, right.

Avalanche devices (TVS, zener, MOV..) are essentially instantaneous.

It's actually worse because spark devices have an ionization period that's voltage dependent.  Like I said, "terrible messy things".  It might break over (at ESD speeds) at 2 to 8kV, but only be rated for like 500-1000V and for that matter only meet regulations at 100V (not that that matters for a signal line).

You'll never get enough voltage for long enough, to fire both, if you use both.  Not without dozens of cm of trace length between them.

Tim

james_s:
Hm interesting, well as one of the analog wizards around here I'm going to trust your judgement on the matter. I read an article at some point that talked about the difficulties in suppressing ESD given the unusually fast rise times and high potentials but I don't remember where I saw that.

Either way I think it can be agreed that the spark gap is not really necessary and it may well be that the engineer that designed the charger did not have a great deal of expertise on the ESD matter and was just doing what seemed like a good idea to them at the time. I often have fallen into the trap of assuming that design choices in commercial products were all done for a good reason however that is not always the case.

Circlotron:
If it was a neon or other gas filled device, shouldn’t it have a dot inside the blue circle to show it was gas filled?

T3sl4co1l:
Yes, and other electrode shapes may apply, though the two circles is pretty standard.  I suppose an air gap doesn't really need to specify gas in the envelope, but there may not be an envelope as such (which seems to be the case here), in which case... a pair of arrows and no envelope would do well enough, really.

Tim

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