Current regulator using NOT gate
simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. OP's circuit redrawn in conventional layout. (Current flow from top to bottom of schematic.)

I think I have designed a current regulator.

If your voltage source is a true constant voltage source then you haven't. The current through RL will be V1/RL no matter what Q1 is doing.
You may be confusing your invention with a shunt regulator.

Figure 2. A shunt regulator block diagram. Source: Electronics Notes

The shunt regulator or shunt voltage regulator is a form of voltage regulator where the regulating element shunts the current to ground.


The shunt regulator operates by maintaining a constant voltage across its terminals and it takes up the surplus current to maintain the voltage across the load.

Source: Electronics Notes
The classic Zener-diode + resistor is one form of shunt regulator but note that it relies on the series resistance. Without that your circuit does nothing but waste energy and, probably, burn out transistors.

Your question title refers to a &quot;NOT gate&quot; and you have tagged the post as &quot;digital logic&quot; and &quot;constant-current&quot;. Is is none of these.

It's not &quot;logic&quot; because it's an analog circuit. While the circuit may remind you of a simple BJT NOT gate it is not working as digital logic in your design and it is missing the pull-up / load resistor.
It's not &quot;constant-current&quot; because it doesn't provide any constant-current regulation. As discussed already the load current depends purely on V1 and Q1 doesn't change it.