Changes between Version 33 and Version 34 of poe


Ignore:
Timestamp:
08/25/2020 05:51:19 PM (2 years ago)
Author:
Ron Eisworth
Comment:

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  • poe

    v33 v34  
    101101Non-isolated designs are acceptable for deployments where the boards ground isn't exposed externally which effectively creates the isolation. In cases where the units ground will be tied into another instrument or supply, this can cause issues if there is a large differential between the switches ground and the unit. In these type of installations, an isolated PoE inserter/injector can be used to isolate the switch from the unit.
    102102
    103 PoE PSE switches typically use high side switching which means the 48V DC output is always present and ground is switched on when the unit (PD - Powered Device) responds with a correct signature. Issues with this configuration can occur when powering multiple boards from the same switch if the boards share a common ground (for example they are mounted in metal cases and then mounted on a DIN rail or shielded Ethernet cables are used which then can create ground paths between the units).
    104 
    105 In these cases, with a common ground between the boards, if one board is turned on by the switch, the other board will then try to power on (or create a fault on the switch) since it will try to utilize the other units ground path. This type of condition can be eliminated if the boards can be isolated to not share grounds. Note this condition can even occur with fully isolated implementations if the units have a common ground.
     103PoE PSE switches typically use high side switching which means the 48V DC output is always present and ground is switched on when the unit (PD - Powered Device) responds with a correct signature. Issues with this configuration can occur when powering multiple boards from the same switch if the boards share a common ground (for example they are mounted in metal cases and then mounted on a DIN rail or shielded Ethernet cables are used which then can create ground paths between the units). In these cases, with a common ground between the boards, if one board is turned on by the switch, the other board will then try to power on (or create a fault on the switch) since it will try to utilize the other units ground path. This type of condition can be eliminated if the boards can be isolated to not share grounds. Note this condition can even occur with a fully isolated implementation if the units have a common ground.
    106104
    107105