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
In practical circuits a resistor would also be used,
usually a cap in one side and a 100/200 ohm resistor in
the other side the resistor would also act as a fuse
This circuit is widely used in plug in industrial
timers and the like, that invariabily have undedicated
relay outputs

--
Peter Cousens
email: peter@cousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem