simulate this circuit – Schematic created using CircuitLab
At a coffee house recently, I saw a napkin drawn schematic at the table before the waitress cleaned up after the previous patron. I do not remember the part number for the P ch JFET, but the N CH was MPF102.
I cannot figure out what the point of such a circuit would be.
It looks to me like the JFETs are going to be biased off unless the voltage rises past the source drain breakdown voltage. Anything that high would damage the microcontroller input pin.
What am I missing here?
Best Answer
The circuit is wrong/useless. Look at the 0V connections - the series combination of J1 and J2 are shorted by 0V. This effectively makes the circuit V1 in parallel with R3: -