I'm puzzled by this application
**broken link removed**
I would like to be able to measure voltages across sections of this circuit, it has a separate common, and my probe points will sense voltage drop across various segments of it (just like I would use a multimeter).
I simplyfied it by putting 3 resistors to simulate voltage drops (R1 might be mosfets drop, R2 motor drop, R3 a shunt resistor) and a medium 200V Dc voltage source (far high from opam supply). I think I need a diff. opamp with a high Common Mode Voltage but:
_ I think I'm pretty ok if I should measure voltage drop across a shunt resistor (R3), I can connect +V and -V of the opamp across the shunt resistor and I get a Vout = (+V) - (-V) referred to the uP board ground (then I can amplify it and so on).
_ what I miss (somewhat) is how can I read the drop across R2? its voltage range span well outside the opamp power supply rails (this problem is no more a common voltage problem), can I use a normal resistive partitioner to reduce the amplitude of the signal, how would I build the input network (or not)?
Can you point me application notes? until now I can only find examples of reading a shunt resistor, or (ina148 datasheet) they cheat, and use a separate power supply rails to supply the input shaping opamp (but again, they read a simple shunt).
Thank you all,
James.