ac voltage measurement without transformer
Hi,
look at this application note by National Semiconductors
www.nsc.com
It decribes an ultra-high isolation amplifier powered by
an ultrasound transducer (!).
The input side voltage is converted to frequency then
opto coupled to a frequency to voltage converter.
Instead of using such a transformer for input side power supply,
you can get it directly from the input AC line with a trasformerless
power supply built with a capacitor, a resistor and a zener diode.
Remeber that in this way you have the maximum circuit simplicity, but
the input side will be exposed to every transient on the AC line, so
you should use all precautions (dischargers & co) to prevent circuit
damages due to spikes and transients.
Remeber also that the input side will be at dangerous potential, so
the opto coupler and the PCB should met your safety standards according
isolation.
i think that with some simple modifications this circuit
will be right for you.
Bye