PowerDsine IEEE802.3 User manual

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IEEE802.3at Task Force
Technical and market considerations
regarding PoEp output voltage range
Vancouver BC, November 2005
Arkadiy Peker
Daniel Feldman
Yair Darshan

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Part A
Technical Considerations regarding
PoEp output voltage range

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Objectives
To discuss optimum voltage range for PoEp
To show advantages of having PoEp minimum voltage of 51V

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HP POE voltage range
Maximum voltage: 57V (safety consideration)
What is most optimum value for minimum voltage?
PoEp group objective; maximum power within practical limit (Power
Dissipation, Safety consideration)
Power dissipation is function of the current
Increasing minimum voltage reduces current level for the same load
power or
Increasing Power delivery to the load for a given current value.
Hence same infrastructure delivers more power to PDs for given
PSE PS size and cost
Bottom line: more applications may supported
– Larger POEp market

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PoEp minimum voltage
Lets assume current is 0.35A and calculate power delivered to the load by four
pairs
It means, that at 51V, for the same power dissipation on the cable, power
delivered to the load will be 4.9W more then at 44V.
The advantage of higher voltage is further increased for higher currents than
0.35A
32.64W27.74WMaximum power
delivered to the PD
3.06W3.06WPower dissipation
on 4 pair
51V44V

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PoEp minimum voltage
Let us look on this issue under another angle assume minimum load need
to be delivered to PD by four pair is 40W
Power dissipation on a cables for 51V PSE will be 2.45W less then for 44V
Advantages of higher voltage is increase with increasing power level
0.890.84System efficiency
for ~500W PSE PS
44.88W47.52WPSE power
4.85W7.3WPower dissipation
on a cables (4P)
0.44A0.54ACurrent per pair
40W40WPd power 51V44V

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PoEp minimum voltage
51V required smaller PSE power supply then at 44V, for the same
load.
The technical advantage is clear for using higher voltage minimum
voltage level for POEp PSE.
Let consider different options in PoEp Power architectures :
- AC input and battery back up
- AC UPS input

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PoEp Power Architecture-AC Input

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PoEp Power Architecture-AC Input
One of the arguments for not using 51V power supply is that back up
battery operates up to ~ 43 - 44V.
However most batteries used in telecommunication have one of the
terminal grounded (mostly positive)
This would prevent direct use of this batteries in POE and would
require to have isolated converter between batteries and PSE
regardless of output voltage considerations
Therefore increasing output voltage to ~51V would not add any
system cost
But boost converter would be useful even in case of isolated
batteries (DC UPS), which really is not very popular power
architecture.

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HP POE Power Architecture-AC Input
Taken at account the voltage drop on a high current battery cable
and PSE voltage drop (Mosfet and CS resistor), it would require
Low Voltage Disconnect to shutdown battery at ~46V in order to
have 44V on the PSE output
It means battery life would not be fully utilize
Adding boost converter, which would keep output voltage of the
system constant, in our case 51V,would extend batteries
capabilities on ~15% in POE systems