stambaughw
Junior Member level 1
I'm attempting to design a 4-20mA loop powered pulse output circuit for a sensor. If you look at sample circuit1, I can easily produce a clean signal across the load resistor using a typical current shunt resistor, load transistor, and an op-amp to control the current through the transistor. Unfortunately I need a reference voltage to generate the necessary voltages to drive the op-amp input. As soon as I add any kind of reference as in circuit2, the input stabilization capacitor (C1) kills the signal rise and fall times of the signal across the load resistor. If I reduce this capacitor, the rise and fall times improve but the stability of the reference decreases causing overshoot and undershoot in the signal. My questions is, how can I generate a reasonably accurate reference voltage (1%) that can supply ~3mA of current to the rest of my circuit? I've attached the LTSpice simulations for reference purposes. Also note that I tested using the LT1498 supplied by the loop power with the reference unloaded and I get the same results as circuit 2. I just used appropriate Linear parts for simulation purposes.