Jon Bertrand wrote:
>
>      Maybe I didn't understand the question but...
>
>      I'd be careful when using a cap to tap off of line voltage.
>
>      When I design anything I always think about stray bandwidth - do I
>      have more than I need?  If so, how are the various impedances in my
>      circuit going to respond to it?
>
>      Ideally, any supply that takes line voltage and steps it down would
>      limit the bandwidth to as low as your circuit could tolerate (it would
>      be a low pass filter).  By limiting the bandwidth you'd cut down the
>      RF, ESD, and transient-type problems in your circuit.
>
>      With a series cap as the voltage dropping element you'd have a high
>      pass filter - the higher the frequency - the easier it would conduct.
>      ESD, RF, Line spikes would all eat you alive unless you put a low-pass
>      filter after the cap.
>
>      It doesn't seem safe.
>
>      ... just my impression...
>
>      Jon Bertrand
>      jonb@cirris.com
I agree you need a transformer if you have for instance lines from your
circuit to the outside like all of mine.What I would like to find is a
transformer that is sized for a 20ma load (miniscule) the ones I am
using take up most of the board space in my designs. Tony M.