I found this circuit [1] and implemented it on a PCB prototype but it just doesn't work at all. I've looked at Auto On/Off part of the circuit and whilst I can see what it's trying to do, the P-Fet Gate is always pulled high by a 100k Resistor so Auto on will never work. Can't see why there's a 0.1uF Cap in there.
Ignoring Auto On/Off and looking at a button press I'm confused by what I'm seeing on the N-Fet Gate so I'm suspicious of the 10uF Cap as well. That N-Fet Gate is pulled high momentarily but then gets pulled down to -5V, which I don't have in the circuit? I've only got a 5V supply voltage connected so I'm impressed with -5V. (Have I discovered free negative energy? ;-)
I'll attach a few scope traces. I'm happy with auto on output and auto off output as I don't see how they would work given the Cap. As for the button press output I've no idea what it's doing.
Channel 1 / Yellow - P-Fet Gate
Channel 2 / Blue - P-Fet Drain Output of my latching switch
Channel 3 / Pink/Purple N-Fet Gate
There is another circuit on a forum post here [2] but it didn't include auto on/off circuit which I thought might be useful so I went with [1]. Given that it's not working for me there is a chance I might learn something. There is a chance over Christmas holidays that I should bite the bullet and learn how to run SPICE on Linux.
Thanks for any ideas
[1]
http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/on-off-power-controller[2]
https://www.eevblog.com/forum/projects/latching-switch/
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