Adjustable Voltage Regulator that operates in the uA region as a Precision Current Regulator?
To use a voltage regulator in this mode requires an ADJ pin current &lt;&lt; output current. They will be difficult to find for 150uA output current.

Better to use a current mirror (low precision) or a current servo (higher precision)







simulate this circuit &ndash; Schematic created using CircuitLab

The current mirror is a very common idiom to get tracking currents. D1 offsets Vbe, in a reasonably temperatutr compensated way. The ratio R1/R2 sets the ratio of the output current to the control current. Alternatively you can simply set the voltage of Q1 base. This is fairly low precision as it depends on high gain in Q1.

The servoed current source is higher precision, as it measures the voltage in the sense resistor itself, rather than with a Vbe offset. As shown, the base current is an error to the output current, so Q2 should have a high and stable hfe for good output accuracy. Q2 can be replaced with a darlington (higher gain) or a PFET (zero gate current) to reduce or eliminate this source of error.