I would like to control and power a 6V/90mA pump motor from my Arduino uno without addition power source.
I came up with a combination of the op-amp + transistor as shown in the following schema:
To summarize and make sure I understood well, I have 2 options (assuming I use a 9V battery):
I hope your not thinking of one of those little rectangular 9V batteries better suited for smoke detectors. That is a really poor choice for any high current needs (and, yes, that includes a 90 mA pump).