Barry Ma wrote:
>
> Please allow me to ask a relevant question only for curiosity.
>
> We have no idea of what charge (positive or negative) would go to the DUT in
> ordinary ESD.
> That's why we have to test two polarities in ESD immunity test.
>
> Lightning is a kind of ESD happened between a charged cloud and
> objects on earth surface. Some figures imply that an electron
> current flows from the charged cloud to the earth. Is it possible
> to have an opposite direction - electron flows from earth to cloud?
If you want to hunt this down, the best man by far is a
Dr. Uman. Considered the world's expert on the subject.
Wrote a classic during the mid-80s titled Lightning.
Believe his Ph.D. is in plasma physics which is the only
way to really understand lightning. I wrote a paper which
tried to do a mathematical analysis of lightning for grad
school, but there's so much more that isn't known about it.
There's much associated very odd phenomena also under the
subject of lightning.
Anywho, once the leader has made a path from the cloud
to ground, there are exchanges back and forth for each
strike. Several strikes adding up to what we see as
"one" bolt of lightning which I'm sure you know. There
are positive strikes, but they are rarer and carry a
great amount of power. A negative strike transferring
something on the order of 50Q from cloud to ground
would be considered "large".
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