I am trying to design a circuit using an intermitent power source (a bicycle hub generator), which is rectified and filtered, and regulated at 6,8V.
Now I want to "detect" when the power source is ON or OFF. I made an experimental circuit (below) to validate the idea that if I put a pull-down at NODE1, when VCC rises above 6.8V, current flows through the zener, the mosfet is activated, and the LED shines.
This seemed to work as expected, but there was some ripple, and the on/off transition was not as sharp as I need. So I thought about using a Schmitt trigger, since I have some ICs around (namely a CD4093BCN). I tried replacing the MOSFET with a double-inverter configuration using two of the IC gates, and the triggering works when I probe the trigger input with a direct wire from Vcc or Ground, but not when I connect the input to
While measuring V at NODE1, I found out it does not rise enough to trigger (does not go above 2/3 of VCC).
My questions are:
- What am I doing wrong?
- How could I properly activate the Schmitt trigger when the Zener is "on"?
- Would I be better served with an OpAmp Schmitt trigger instead of a Logic-Gate one?