>> > only by pressing a button to turn on.

The circuit I posted does that. And allows the PIC to hold itself on 
and then turn itself off when desired. Off current drain is 
essentially zero.

______________________

The following Microchip circuit

> See http://ww1.microchip.com/downloads/en/DeviceDoc/40040b.pdf
> Page 14, "TIP #11 VDD Self Starting Circuit".

Is clever BUT will only work for circuits where the Vbattery is not 
much more than Vdd. This is because the voltage doubler from the clock 
must provide enough voltage to hold on the NFET. To do this the gate 
must be above battery voltage by Vth (Vthreshhold) for the FET. Vth 
ranges from about 1 to 6 volts depending on FET. For Vdd= 5v then 
Vdoubler is about 8 volts so Vbattery can only be about 6 or 7 volts. 
This principle COULD be extended to work with larger battery voltages 
but will probably need more components.

A similar arrangement with a PFET where the capacitively coupled clock 
signal pulls the gate negatively towards ground would work with any 
battery voltage.




        RM


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