Diff Amp VCCS for 0-165mA control

Standard Diff Amp topology, gain of 300. Will give 0-165ma output for 0-4.95V control voltage (Voltage Controlled Current Source; control voltage shown on the right). When I actually build this I may use an off the shelf instrumentation amp instead of the diff amp so there is no loading of the sense resistor voltage. UPDATE: If you are connecting the instrument requiring a current source controlled signal between the output of the top op-amp and the sense resistor, you have to keep a couple things in mind. 1) you need to know the input impedance of the instrument and factor this into your voltage divider, and then gain equation and 2) If the input impedance is relatively large (mine is 100 ohm) the top op-amp needs to be 24V capable AND capable of driving 165mA+. So this isn't a great idea for 0-165mA after all, because finding an op-amp that meets those specs is super difficult, especially a rail-to-rail model. But this could definitely be a nice circuit for a 4-20mA instrument.

published 9 years ago