Hi I'm designing for a PT 100 RTD and found some good information but am curious if anyone knows the difference between some of the current sources I'm seeing.
1. The file link I've attached is a white paper using the MCP609 and looks good but seems more complex than it needs to be. Why they don't just use the simple op-amp follower with a darlington bjt output driving a sense resistor on the emitter side? Is it just to avoid using a transistor or are they getting much better regulation using 2 op-amps?http://ww1.microchip.com/downloads/en/appnotes/00687c.pdf
2. Using the op-amp follower with a darlington bjt output driving a sense resistor on the emitter side technique it seems to me that the base current is unaccounted for if using the collector side for the DUT. You'd be off a the few milliamps it takes to activate the transistor. Am I missing something on that because no one seems to mention it?
I'm not an everyday circuit designer so I don't have all the little tricks in my head regarding op-amps anymore...
1. The file link I've attached is a white paper using the MCP609 and looks good but seems more complex than it needs to be. Why they don't just use the simple op-amp follower with a darlington bjt output driving a sense resistor on the emitter side? Is it just to avoid using a transistor or are they getting much better regulation using 2 op-amps?http://ww1.microchip.com/downloads/en/appnotes/00687c.pdf
2. Using the op-amp follower with a darlington bjt output driving a sense resistor on the emitter side technique it seems to me that the base current is unaccounted for if using the collector side for the DUT. You'd be off a the few milliamps it takes to activate the transistor. Am I missing something on that because no one seems to mention it?
I'm not an everyday circuit designer so I don't have all the little tricks in my head regarding op-amps anymore...