Re: gEDA-user: OT: DC power feed on xDSL circuits

[Ineiev <ineiev@xxxxxxxxx>]

Hello, Michael,
On 1/14/10, Michael Sokolov <msokolov@xxxxxxxxxxxxxxx> wrote:
> 1. What is the benefit from having the DC blocking capacitor across the
>   centre split in the transformer's primary winding?  What harm would
>   there be if someone took that capacitor off the BOM and simply
>   shorted those pins on the transformer to make the primary winding
>   effectively non-split?

My guess is that in some cases there may be unintended DC bias
which could put the transformer core into non-linear region.
I think if DC conductivity is needed it should be provided with
another part.

> 2. Suppose that I do want my CO-side terminal unit to provide DC power
>   feed on the line - say, to power a mid-span repeater.  Where would I
>  need to connect my DC power source?  Would it need to be connected
>  across the centre split of the line transformer's primary winding in
>  parallel with the cap, or would it simply go across the copper pair
>  instead?

As I understand, it should _not_ be connected across the centre split for
the same reason (DC current will run through the transformer).

>    Some of those SDSL transformers (which are all custom parts) were
>    apparently designed for fairly high DC current, so it seems like
>    connecting the DC power source (or load) across the centre split is
>    the way it's done.

I have no idea; probably, those transformers could be used for different
purposes.

Regards,
Ineiev


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