Guys, I've been having a few problems and thought I had maybe found a big problem with my schematic, which may have been causing people some serious problems in replicating this circuit.
When I was originally having issues designing this circuit, I was sure that the 100K pull-down resistor across the gate-source was the solution to my problems. However, I encountered more problems with the circuit when my PCBs arrived.
I had a bit of trouble replicating the problem on the breadboard, but have intermittently had issues since I finished designing the PCB. I've now had the same problem with the new surface mount components, the circuit was shutting off immediately instead of safely shutting down.
I was coming on here to post that the solution was to change the pull-down resistor for a pull-up resistor. This means that you would connect the 100K resistor across the gate-drain instead of gate-source. However, this is only working in some instances e.g. for my surface mount components. I can't get this to work for my TO-92 2N5460 JFETs.
Some of the datasheets for these JFETs state:
Code: Select all
Note:Source & Drain are interchangeable
I tested this a while back and it turned out not to be entirely true for this application. For this circuit, the JFET only works in one orientation. Other people have described similar symptoms so I'm hoping if you try switching the resistor over to the other side of the JFET, you may eliminate the problem.
So in summary: The Source still connects to Ground, and the Drain still to EN (via the switch), but the 100K resistor bridges the Gate and Drain. Give it a try, hope it works.