Zener series resistor
The resistor is a tap and the Zener is an overflow drain: whatever the load does not drink spills through the diode.
R = (Vs − Vz) / (Iz + IL) Pz(no load) = Vz × (Iz + IL)
Simple shunt regulator for small loads. The resistor is sized for the lowest supply and highest load; with the load removed, the Zener absorbs everything, so check its power rating. Use a regulator IC above a few tens of milliamps.