I am attempting to trouble shoot a circuit and I am a bit stumped. The circuit is high current source (10-20A) based on a master-slave configuration using OPA549 high power op-amps. There is one master and 4 slaves. A set point voltage controls the current depending on the load resistance. In this case the load is wire wound coil with 1 ohm resistance.
When the set point voltage is positive the circuit works as expected. However, when the set point is negative the circuit exhibits oscillation about the set point. From reading, I realize such configurations suffer from stability issues when driving capacitive loads, but I imagine the load in this case is predominately resistive and inductive in nature. Maybe a variations in the op-amps lead to them fighting to regulate the output and I should increase the isolation resistance at each output. However, I am puzzled why I only see oscillations for negative voltages. Both supply voltages also show oscillations when the set point is negative as well. I suspect the oscillations in the supply voltages are caused from the variable current draw of the op-amps and not the other way around. The output voltage (labelled N1) and the AC coupled supply voltage are shown below. Any thoughts would be greatly appreciated. Thanks in advance.