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?
simulate this circuit – Schematic created using CircuitLab
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.
Best Answer
simulate this circuit – Schematic created using CircuitLab
Do this instead.
A bridge is a voltage doubler unless you connect the centre tap also to 0V then it becomes a half bridge.
33R load is possible with 33R series then voltage is 50%. No load is always 50% more due to rms-pk (rt2=141%) xfmr loss 8~10% thus 141%+10% - diode drop~ 150% of RMS with no load.
Choose Vf of LED to tune active clamp.