I have a DC (Audio type) Power Amplifier, on +/- 40-volt rails, in which I want to "Current-Sense" the output (for instrumentation - not protection).
Typically this is done with a high value input resistor Instrumentation Amplifier. However the process of removing the Common Mode Voltage (say minus 35-volts) results in voltages in the order of milli-volts at the INA input (because of high value "dropping" resistors). This then requires amplification by 100 to 1000 to suit the following stages (Feedback or ADC).
A better way would be to translate the Power Amplifier "sensed current" via current, to +/- 5-volt lower voltage grounded circuitry. If current could pass from the high voltage stage to the low voltage stage (rather than voltage), that would work better.
The OPA860 looks interesting in that it is a "Voltage to Current" converter with a BIPOLAR output - unlike most Power Supply type Current Sense Amplifiers.
I have Floating +/-5 volt supplies - so powering it isn't a problem.
However, the OPA860's B,C and E pins are restricted to power rail voltages (+/- 5 volts) - so I couldn't pass that current (1mA) down (across a 35-volt drop) to a grounded 5k resistor for instance. I'd need a part with a large "Vce" voltage like "Vce = +/- 50-volts".
Is my reasoning here correct, or is might it be possible to make this part work?
It is the BIPOLAR opration that makes it so interesting.
Does the OPA860 have good linearity around zero?
Understanding what I am trying to achieve, does TI have another solution that might work in this current translation sense - or in general?
Thanks
Peter