Hi Felix,
I'm trying to understand the circuitry to to refresh my analog knowledge, as I've been doing digital only the last few years. Finally I'm trying to build my own current meter, but this is only a private project (non commercial, most likely for me only). So, part numbers would help for the build, but giving me hints on what to take care for during the selection process of the FET would help me more to improve my knowledge. On a first shot, I would look for low Rds_on, but what are other main characteristics?
Rdson lies in the microohm range, which is probably the reason why it can be ignored for the micro ampere scale. If I understand the schematics correctly, in the milliampere range, Rdson adds to the burden voltage, but not to the measured value.
Based on your reply, I think following specs are important:
- low Rdson
- low DS/GS/GD Leakage
How does the FET introduce noise (which parameter should be low/high)?
I understand if you don't want to help me forking your project, please let me simply know in this case. I somehow assumed your project was open hardware, but maybe I got that confused with the uCurrent.
Kind regards,
Lasse