RE: [802.3af] Clarification- to the propose text
Roger,
You
are correct with your analysis when PSE is connected to an other
PSE.
And as
the standard specified today we don't need special circuits to handle this
situation.
Yair.
Hi
here is a clarification to the proposed
text:
I propose we tell designers to test their PSE and their PD
both
to a 'Hot' PSE - (opposite And same polarity) and
be done with this.
so here is the text:
"The PSE must tolerate the
application of a voltage of the same and of opposite polarity
(up to 57v)
From another PSE*
without incurring any damage when
such potentials are applied for an indefinite amount of time."
*
cause that PSE would be current limited to a max of 450ma and we assume is to
be shut off.
here we may choose to use a non PSE test when PICS is
written....
so the 'other' PSE may be a power supply with a
limited current of 450ma...
reasons:
some vendors (chips and
system) already have put together hardware
with opposite polarity to what
we all agree to, and feel like we do not have
the right thing going
here.
also for such a scenario to take place the following has to
happen:
1- Both PSE's must fault (not discover before powering) or
both be ' HOT '.
we worked hard to insure this does not happen --in
af.
2- We have a parallel diode that we specd (paid for) at the PSE end
that takes care
of a hot-plug the current can return to the originating
PSE.
At the same time the diode helps a PSE discriminate by polluting
anything in the other PSE
that resembles a signature insuring no false
discovery of another PSE.... No Hope here this
better be reality or we are
in bad shape.
3- Even with all PSEs following a single polarity a cross
over cable would take us back
to the same problem again?!- if the PSEs are
Hot - what am i missing.
That was my 2c for
today,
roger
Hi
I propose we tell designers to test
their PSE and their PD both
to the 'Hot' - Opposite polarity and be done
with this.
so here is the text:
The PSE must tolerate the
application of a voltage of equal and opposite polarity to its
own without
incurring any damage when such potentials are applied for an indefinite amount
of time.
reason:
some vendors (chips and system) already have
put together hardware
with opposite polarity to what we all agree to, and
feel like we do not have
the right thing going here.
also for
such a scenario to take place the following has to happen:
1- Both
PSE's must fault (not discover before powering) or both be ' HOT '.
we
worked hard to insure this does not happen --in af.
2- We have a
parallel diode that we specd (paid for) at the PSE end that takes care
of a
hot-plug the current can return to the originating PSE.
At the same time
the diode helps a PSE discriminate by polluting anything in the other
PSE
that resembles a signature insuring no false discovery of another
PSE.... No Hope here this
better be reality or we are in bad
shape.
3- Even with all PSEs following a single polarity a cross over
cable would take us back
to the same problem again?!- if the PSEs are Hot -
what am i missing.
That was my 2c for
today,
roger