Hi Joris, Lennart,
Based upon this discussion, I referred to the PSE section to try
to determine what is actually interoperable. Figures 145-24 and
145-25 show the lower bound limits of what a PSE must support.
These limits have the current transient (Ilim) region up to Tlim
min, and then there's an immediate drop to Ipeak (which is
calculated with Ppeak_PD). If Ttransient starts at the beginning
of the transient and ends at the existing limits, then
interoperability is guaranteed. If we change this rule to start
Ttransient at the end of the step, then the PSE may shut down the
PD if it doesn't meet Ipeak immediately after Tlim_min (in fig.
Note that the lower bound Ipeak and Icon limits at the PSE are all
voltage dependent by the equations used to generate them. At the
end voltage of the TR1,2 steps, the PSE Ipeak and Icon lower-bound
limit values are lower: If we assume that a PSE would never
instantly decrease it's current output capability to meet this new
lower boundary, then there is a valid reason to extend the time
On 11/3/2017 9:12 AM, Joris Lemahieu
Lennart and Ken,
think the easiest way to solve this is to take the reference
when the transient voltage is complete (Vpse constant and
this is the only reference point for which all simulated
Pclass_PD and Cport combinations pass.
interoperability, it might indeed be better to add the
requirement to the TR1 and TR2 that the PD may not force the
PSE to be current limited to IIim,min more than Tlim,min.
principle I’m not against Ken’s suggestion to increase
Ttransient and take another reference point.
only fear this could lead to a longer discussions.
we still want to take this path then I would suggest
deducing the values from the following constraints:
the AC power waveform, define the Transient Energy =
(Ppeak_PD – Pclass_PD)*Tlim,min
apply this to the Cport: ½ Cport (Vfinal^2 – Vinit^2).
gives one maximum value Cport
requirement that the PSE may not to be current limited to
IIim,min more than Tlim,min gives another maximum value for
the minimum of both Cport values and define based on this
capacitance the time the PD may exceed Ppeak_PD or
If there's currently no interoperability issue for 180uF and
360uF, then selection of the starting point only places a
burden on the PD with respect to the test. It's not clear to
me that the test accurately reflects what a PSE will allow
before shutting down, but in any case, I thought starting
Ttransient at the conclusion of the step might have changed
the test from its initial intent and simulations. If actual
interoperability is unaffected by it, then selecting the end
of the step is ok, however I would suggest increasing
Ttransient rather than starting it at the end of the step, to
avoid ambiguity with respect to current limiting at the
On 11/1/2017 10:15 AM, Lennart Yseboodt
I checked the simulations.
With the reference taken as when the
system goes into a current limiting mode, at least Class 8
and Class 4 flip from OK to failing the transient
requirement (with a 360uF and 180uF cap respectively).
Other Classes may also be affected, I
While I also am glad to see the
"intrinsically OK" text gone, it should be our goal to
make it such that PDs with capacitors of 180uF and 360uF
do not need special provision to deal with transients.
That is after all the basis on which
TLIM and ILIM have been chosen.
Given that there is no interoperability
issue with the reference taken when the voltage transient
is complete, I fail to see why we should increase the
burden on the PD ?
On Wed, 2017-11-01 at 09:48 -0400, Ken
The TR1,2 are steps with a rise-time, however they are
also described as having a current limit. If the source
current limiting kicks in, then the end of the transient
doesn't occur until the limiting ceases. The easiest
reference is the beginning of the transient because there
are no ambiguities.
I think this was the intent early-on, however as you
point out, the rules aren't clear, and neither are the
origins (at least in a quick search). The existing text
doesn't explicitly reference the beginning:
During a transient the input power of
the PD may exceed PPeak_PD or PPeak_PD-2P.
Table 145–30 defines
three PSE output voltage transients.
When transient TR1 or TR2
is applied, the PD
shall meet the operating power limits after
defined in Table 145.
However If the intent was to reference the end of the
transient, I would think the second sentence would have
AFTER transient TR1 or TR2
is applied, the PD shall meet the operating power
limits after TTransient as
defined in Table 145.
In any case, the TR1,2 test requirements are an extreme
corner case and there's no longer any suggestion to the
reader that specific capacitances will "intrinsically"
pass, so I don't see a problem with the reference being at
On 11/1/2017 8:29 AM, Lennart
The PD not spending more than 6ms
or 10ms in the current-controlled mode is also
something the PD should meet.
We currently do not have a
requirement for this (ie. it is possible to meet
TR1/TR2 but spend more than TLIM in the input current
Note that all Class/Type
combinations currently do not violate TLIM.
The current text does not offer a
reference for Ttransient. I picked the end of the
source transient because it is an easy to find point.
If we shift the reference point
backward in time, the PD margin decreases and we may
have to increase ILIM to TLIM to make things work
- Should we add a requirement to
the TR1 and TR2 that the PD may not be current limited
to ILIM for more than TLIM ?
- Given that currently there is no
issue with TLIM, do you still feel we should move the
reference point back ?
On Mon, 2017-10-30 at 09:39 -0400,
The new text: "referenced from when the ‘final voltage’ is reached at
the source", sets a time boundary which is after the time that the PD
starts to violate Ppeak_PD. Seems like it should start at the beginning
of the transient, so that the PD Peak excursions that are beyond
Ppeak_PD are no wider than 10ms and 6ms, to match Tlim_min in the PSE
On 10/29/2017 10:09 AM, Lennart Yseboodt wrote:
Attached proposed baseline for the PD transients section.
At the September meeting it became obvious that Table 145-30 wasn't
I've re-simulated all of the transient conditions and, except for
Class 7, everything is OK.
We may want to consider increasing the ILIM for Class 3, Class 4, and
Class 8 to make it such that PD's that "intrinsically" should be fine
See simulation_annot.pdf for simulation results.