I have an opamp configured as a constant current sink like this:
As you can see, the reference voltage for the SENSE pin is set by the voltage divider on the left. This requires a stable voltage on VCC - if it varies, so will the set voltage and thus the current passing through Q1.
I'd like to be able to run the opamp off a supercap or unregulated battery as a power supply, which means VCC won't be entirely stable. Is there an alternative topology for the opamp that achieves the same result without requiring a stable voltage source, or the introduction of an LDO or voltage reference?