I am having trouble on a 4-20mA current loop circuit that I have prototyped (4 layer board). The circuit is not working properly. The output has large oscillations occurring at a regular intervals.
I am trying to determine the source of the issue. I do know that the opamp signal driving the transistor base is incorrect. It is a pulse wave instead of a static voltage. The bread board version I built works properly and shows a near static voltage.
I am looking for any suggestions on where to go with the issue. I thought I would try and simulate the circuit but am having trouble getting LTSpice to work with my negative voltage references. I've attached a copy of the pertinent portion of the actual circuit, and image of the simulation circuit that won't run and the LTSpice schematic and a snapshot of the transistor base voltage.
Thanks is advance.
I am trying to determine the source of the issue. I do know that the opamp signal driving the transistor base is incorrect. It is a pulse wave instead of a static voltage. The bread board version I built works properly and shows a near static voltage.
I am looking for any suggestions on where to go with the issue. I thought I would try and simulate the circuit but am having trouble getting LTSpice to work with my negative voltage references. I've attached a copy of the pertinent portion of the actual circuit, and image of the simulation circuit that won't run and the LTSpice schematic and a snapshot of the transistor base voltage.
Thanks is advance.
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