modem help

From: J.C. Wren <jcwren_at_jcwren.com>
Date: Sat Oct 26 15:01:01 2002

        It should be stated (and obvious) that you can ONLY safely do this with a
transformer coupled supply. Otherwise you potentially have the classic "hot
chassis" condition. And be sure to consider the effect on things if you
were to build a device that had a serial connection or somesuch powered off
the same transformer.

        This technique works fine, but is not without peril if you don't fully
understand what you're doing.

        --John

-----Original Message-----
From: cctalk-admin_at_classiccmp.org [mailto:cctalk-admin_at_classiccmp.org]On
Behalf Of Jim Kearney
Sent: Saturday, October 26, 2002 15:41
To: cctalk_at_classiccmp.org
Subject: Re: modem help


> Very... The only full-wave rectifier you can get without a centre-tapped
>input is a bridge, and that doesn't have a common connection between
> input and output for one thing. It also only gives a single polarity
> output.

...

> Basically 2 half-wave rectifiers, each accepting one half of the AC input

There is a useful way to use a bridge to do this. It wastes half of it,
but it's a single component that doesn't need its leads formed instead of
two that do, so I often use it. Probably not cost effective for mass
production, though.

     +--------+
     | |
-----| ~ + |-------+---------------- +V
     | | |
--*--| ~ - |-------(----+----------- -V
  | | | _|_+ _|_-
  | +--------+ ___ ___
  | | - | +
  +-------------------+----+----------- gnd
Received on Sat Oct 26 2002 - 15:01:01 BST