Minimal circuit for a current limiter for small dc voltages and low power
It doesn't have your Zener, but I've always like this current limiter circuit:







simulate this circuit &ndash; Schematic created using CircuitLab

Very simple to use - just set \$R_{sense} = \frac{0.6}{I_{limit}}\$.

The tradeoff for that simplicity is (1) efficiency and (2) precision:


There's up to 0.6V of voltage drop across \$R_{sense}\$ in series with
your load. In many low current limit circuits this is not an issue,
but in power efficient circuits this will definitely be an issue.
There's a fairly vague transition region around the current
limit, which is sensitive to the \$\beta\$ gain of the transistors.


But if efficiency and precision aren't high on your requirements list, it's a winner!

There are plenty more alternatives here: Current limiters using transistors and diodes