Mark said:
Thanks. Actually I'm looking for a way to switch on power to a
PIC16LF876A design running from a single lithium ion AA battery
(4.2v-2.5v.) The design only has one button, so a low-going signal must
turn it on (and consume next to nothing when off.) I was wondering if a
4013 connected to Vdd and Vss via this button, could be turned on by the
button (which then latches and powers up the PIC.) A MOSFET was also a
consideration, great off resistance but it's hard to get good conduction
with only 2.5v gate voltage. K.I.S.S...
-M
The 4013 _is_ a MOSFET design, so there's no free lunch there. There
are 3.3V "Logic" MOSFETs out there, so there's hope.
Use a P-channel MOSFET to turn it on, with an NPN "logic" transistor
from the PIC to keep it on. Connect the gate of the MOSFET to the
transistor collector and the switch. Make sure to scan the state of the
switch on power up, or delay for a bit when you turn on -- I've had
power supply decoupling caps bounce up in voltage when the current drain
is removed, turning the uP back on.