I am using an STMicro TL084 Opamp in a buffer format and wondering why i keep hitting the Open Circuit +12V voltage rail.
There are 2 possible connections in the below image, the first being the external 12V connector that has a 4-20mA signal. This actually works fine when its plugged in and the target voltages are met. When this was disconnected I found that the ADC-OUT would ramp up to 12V so I started playing around with a pullup resistor to see what current was required before it began to act as a buffer again. Using my resistor decade box, a 1k pullup still had the output regulating at ~12V. When I moved it to a stronger pullup (only steps I have on it), it started to regulate at 3.3V correctly.