On 8/15/2011 4:46 PM, Owen Duffy wrote:
Jim wrote in
:

...
Most UL listed wall wart power supplies these days can hold off
several thousand volts between inside and outside (that's the so
called "hi pot" test rating).

That may be so at DC or 60 Hz, but it may be relatively transparent to
the spectral components of lightning discharge current, components that
may me significant to 100MHz or more.


yes.. although for the most part, if you're looking at the transient
from a "spark gap arrested lightning impulse" you probably don't have
quite that spectrum.


There is no simple broadband equivalent circuit of the power
transformer, but at 100MHz, it might look more like some series
capacitance of the order of 100pF from primary to secondary for common
mode excitation... and that may well allow damaging currents to flow
(without insulation breakdown or permanent damage to the transformer),
whether driven from the coax shield, the power line, or more likely,
both.

Could be.

Standler's book on transient protection comments that several studies
have shown that most modern consumer electronics can tolerate standard
transient impulses (both the 1 us and 6 us rise time variety) of several
kV. The not so halcyon ESD days of TTL gates connected directly to the
device connector pins are long gone.




Just another factor that makes design of bullet proof solutions so
challenging.

Owen