IEEE802.3at Task Force Technical and market considerations regarding PoEp output voltage range Vancouver BC, November 2005 Arkadiy Peker Daniel Feldman Yair Darshan www.powerdsine.
Part A Technical Considerations regarding PoEp output voltage range www.powerdsine.
Objectives To discuss optimum voltage range for PoEp To show advantages of having PoEp minimum voltage of 51V www.PowerDsine.
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.
PoEp minimum voltage Lets assume current is 0.35A and calculate power delivered to the load by four pairs 44V 51V Power dissipation on 4 pair 3.06W 3.06W Maximum power delivered to the PD 27.74W 32.64W 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 www.PowerDsine.
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 44V 51V Pd power 40W 40W Current per pair 0.54A 0.44A Power dissipation on a cables (4P) 7.3W 4.85W PSE power 47.52W 44.88W System efficiency for ~500W PSE PS 0.84 0.89 www.PowerDsine.
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 www.PowerDsine.
PoEp Power Architecture-AC Input www.PowerDsine.
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.
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 www.PowerDsine.
PoEp Power Architecture-AC UPS www.PowerDsine.
PoEp Power Architecture-AC UPS Cost of power supply with 44V or 51V outputs is approximately the same. But under the same conditions, 51V output power supply will have higher efficiency then 44V PS Estimated cost of additional boost circuitry for supporting the change from 45V to 52V for 500W power supply is about 10% cost of power supply. www.PowerDsine.
PoEp with Boost circuit Lb Db Qb AC POE PS Cb R1 PWM R2 Rs Battery www.PowerDsine.
PoEp with Add Power + AC or Battery Add Power Circuit + Vout 51V + POE PS V<51V - - •For 48V 250W power supply, maximum power for add power converter would be (52V-48V)*(500/48)=42W or about 9% of 500W PS cost •However taken in account improved system efficiency, total cost of ownership would remain about the same www.PowerDsine.
Conclusions Increasing minimum PoEp voltage from 44V to 51V would increase overall system efficiency Costs of 51V PS and 48V PS are approximately the same and from technical point of view would be beneficial to have minimum 51V in PoEp PSE Regardless of output voltage consideration, adding boost circuit for system with batteries back up, would increase battery useful life in POE systems www.PowerDsine.
Part B Market considerations regarding 802.3at output voltage range www.powerdsine.
802.3af modular installed base considerations 802.3af minimum PSE voltage: 44V Modular switches – 44V power supply is deployed with chassis – Customer expectation: 802.3at-blades added to 802.3af-chassis – 51V minimum at PSE Æ Boost converter MUST be placed on blade More power dissipation at blade More components added to crowded blade www.PowerDsine.
How to solve the conflict The Conflict is: – 51V is the Technically preferred solution More power at low cost Bigger addressable market – 44V addresses the existing modular installed base Impossible to replaced 44V power supplies on the field www.PowerDsine.
How to solve the conflict – PD side Proposed Solution Effects on PD specifications – PD operating voltage range: No effect. Remains 37-57V. – PD classification in 802.3at (including Class 4) should be mandatory and not optional – The enhanced classification table will be divided to two parts: (See details in “An Extended Classification Proposal- Proposal #1, Vancouver BC, Nov. 2005) Part a: power classes that can work with either 44V or 51V.
How to solve the conflict – PSE side Effects on PSE specifications – PoEp PSE minimum voltage is 51V. – However PSE's that have a 44V minimum output and are 802.3atcomplaint in any other aspect, are anyway able to power 802.3atcomplaint PD's with classes of Part (a). (Hence all OK so far..) – Supplies power only if capable of (Like we do today in IEEE802.3af) – 802.3af PSE classification including class 4 should be mandatory (In order to PSE to know if to power or not) To differentiate between 802.
Summary The conflict level is pretty much reduce by the previous recommendations Compliant 802.3at PSE is the one with 51V minimum Physics allow to support most of the higher power classed even with 44V ((enhanced classification part A group). which is built in benefit however it doesn't concerns the other standard requirements nor affect it. It is perfectly OK that Switch/PSE is 802.3at compliant as long as its Power Supply supports 51V. If PSE PS Power Supply is 44V, then 802.
Discussion www.PowerDsine.
References An Extended Classification Proposal-Proposal #1. Yair Darshan, Vancouver BC, November 2005 www.PowerDsine.
Annex A: Enhanced Classification table Example for group A and group B With Pmax=40W Group B www.PowerDsine.
