[plug] Telstra CLI/CID Question

[John Summerfield]

> 
> Most modems (especially the older ones) have an isolation transformer 
> that is meant to be rated at some obscene isolation voltage (2kV?). 
> The connection to the phone lines was directly to one side of the 
> transformer with the other side to the circuitry.

Exactly, tough I didn't know the details.


> Some of the newer modems have probably done away with the old 
> isolation transformer and are probably using optocoupled isolation 
> with an internally isolated power supply (there are available potted 
> power isolators, about 10mm x 40mm x 10mm which tansfer 5VDC power 
> across an electrical isolation of 1kV. Don't ask me how but they 
> can...).

A device (such as a LED) shines (or doesn't, as nneded) a light on a 
photo-sensitive device casing it to switch in sympathy. The physical 
separation and dielectric characteristics determine th isolation; 
presumably at 1kV+ the margin of safety they emit the magic smoke that's 
so hard to put back.

>

-- 
Cheers
John Summerfield
http://os2.ami.com.au/os2/ for OS/2 support.
Configuration, networking, combined IBM ftpsites index.