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Hi Steve, Thanks for the review. See my answers
below. Yair From:
owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Yair, I have a few comments:
Yair: We agree that current sharing can be
implemented in many ways including functional isolation.
From standard point of view it is dead issue.
From practical point of view we can use current sharing without isolation hence
Idiff (max current difference between pairs when the current is in the range of
Icut) is required to be in the specification in order to allow any kind of
implementation. VERY IMPORTANT COMMENT: isolation between the
4P PD which is based on 2x2P is not mandatory. It depends if it environment A
or B. Only B requires isolation. A can use isolation or active current sharing
or nothing pending on the power and implementation. ---------------- We’ve
already agreed (or at least I think we have) that a 4P system will consist of 2
independent 2P systems. Yair: Yes we agree on this concept. ------------- The two
power sources can have voltages that differ by several volts, and may be on
completely different grounds, again with several volts difference. Yair: This is true for ENV B
configuration. In ENV A the voltage difference is around 1-2V or less.
Due to that facts we have two options: a) The PD will support worst case i.e. largest
voltage differences. b)
The PD will support max voltage differences pending the advertised ENV
A or B.
I would support in option b) since it allows using active linear means with low
power dissipation in many ENV A applications which is the larger part of the
market.
Using option a) will kill a lot of current and future application. ----------------- So
no form of linear current sharing (before the input to the converter inside the
PD) will be practical because of heat dissipation. Yair: I agree however see my solution
above. It is ENV dependent. --------------- Therefore,
any PD that draws power from more that one PSE must have isolation between the
inputs. Yair: I disagree. See my distinction between
ENV A and B. -------------- When
you have isolation, current sharing is inherent, although not perfect; the
converter with the lowest input voltage will draw more current, but the current
ratio shouldn’t be too severe. Yair: I agree. Isolation is one of the
implementation to get inherent current sharing but not the only one in ENV A. -----------------------------------------------------
Yair: This conclusion of general N pairs
system is a direct outcome of the 2*2P concept. We don’t have to address it in the
standard. It don’t cost us anything. It is implementation issue and I
might say a good outcome. It allows future expansion of the PoE technology. The fact that we can not picture N pairs
application now is normal in new technology. The issue is that our standard
will not block new applications in the future. --------------------------
Yair: Load sharing between N pairs can be
done easily however it is out of scope for us now to show how to do it. The
issue is how not to block it. When the need will rise simple solutions will be
found too. --------------------------
Yair: This is valid argument. Why people
buy 1port PSE and not using wall adapter?. Probably they have found some
advantages. You can never know. ------------ From:
owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Hi
all, Please
find my action item for tomorrow's meeting. It
is revised presentation from May meeting that focus on the concept 4P=2x2P and
the more general case of N Pairs = Nx2P.. Please
feel free to comment. Thanks <<Flexible PD implementation driven
Architecture 002.pdf>> Yair
E-mail: <mailto:yaird@xxxxxxxxxxxxxx>. |