Re: differential amplifier

Why not use a simple linear optocouple with the diode side actoss the output
voltage and the tranny side feeding the control circuit.

this is pretty standard stuff for true "isolated" power supplies. Should
work in this application as well.

great CMRR!




<miso@xxxxxxxxx> wrote in message
news:1158953327.241857.123770@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

ksoner wrote:
Hi;

Have you tried to design a difference amplifier with ordinary low cost
op-amps and resistors. do you have a succesful circuit to share with
high CMRR? I want to read a high DC voltage but DC voltage notr is not
connected to my power supply notr, they are isolated. thats what I need
to do. any other idea to read that voltage rather than a differnce
amplifier? the output should be linear of course from 0 to 400V. thanks
in advance...

Maybe an out of the box solution is best. Can you devise a circuit
where the op amp positive rail is at this high voltage, while the
negative rail is set with a voltage regulator in a manner where the
voltage across the op amp is within its specifications. Then V to I the
differential voltage down to a resistor with one side at ground.

Note this is not isolation, but just a scheme to get the differential
voltage back down to a potential near ground.



.

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