Yes I should have stated the app.
I have a network with RS485 + power (9-30v) on the wires. I'd like to have a small box to plug my RJ11 connectors in that isolates both the signal (that should be easy) and the power. The theory being that if I need a single node or maybe a few nodes to be isolated I just plug in this box.
As I said before I'm sort of happy to have a reduced V on the output, as long as it's about 9v or more the nodes will be happy, but that does place a limitation on the input as it has to have enough headroom over the 9v. However as the nominal system power will be 12 or 24 volts this wouldn't be a problem.
If I go this route then I can use any DC/DC converter.
Rob