Re: hi freq's and computers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


 > Original poster: "Mark Broker by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<mbroker-at-thegeekgroup-dot-org>
 >
 > You're going to have to explain to me why it matters if the PC is
 > functioning.  As I see it, all the cords and cables act as antennas.  The
 > ICs and other goodies on the "inside" of the computer doesn't care if the
 > circuit is powered up or not for the HV, RF "stuff" the "antennas" picked
 > up to fry the circuits.

Actually, whether the circuit is powered up or not can have an effect on
it's susceptibility.  Here's an example.  Say you have an output from a
logic gate, say going to a printer. Unpowered, there may be some sort of
means for a voltage applied to that signal to propagate back through the
circuit, possibly through some parasitic diode to the supply rail.  Powered,
on the other hand, that parasitic diode will be reverse biased, and the
output is being driven by, effectively a low impedance, (sometimes, even,
essentially a short to either the positive supply or the ground rail, for a
classic CMOS output), so an induced transient is conducted to a low
impedance source (i.e. the power supply)

For many sorts of FET circuits, the order of bringing up the supply voltage
is critical to avoid forward biasing parasitic diodes and causing latchup.

The problem you face is akin to the "hot plug/unplug" problem.