Following up on my previous question, I tried this simple circuit to ensure that there is a minimum load on my power supply (to prevent the unloaded supply from rising above Vmax of a part). I actually built this and it works as I expect, but I wonder if there are any additions that should be made to improve its performance?
My idea is, if the load (Rload) is disconnected or not drawing at least a minimum current, the supply rail will rise because of inadequate current through Rsource. When the voltage reaches 9.6 (Vzener + Vbe), Q1 will start to turn on, and will sink enough current (and turn on the "Overvoltage" LED) to keep the rail below about 9.6V.
If the load is drawing enough current, the zener/transistor circuit will be inactive.
Incidentally, I believe that just a zener alone would be sufficient, except that it would have to shunt all the excess current itself. By adding a higher-power transistor Q1, a lower-power zener can be used.