Automatic turn off

[AMay]

Melanie:

Thanks for the help.

I want to eliminate a need for an "on-off" switch, only a push button on, and auto off after a period of inactivity. I will be using 9 volt batteries, therefore off needs to very close to 100% off. 9v batteries provide a rather wide range of voltages, depending on the type, alkaline, ni-cad., or nimh.

Starting with the information you provided, I developed the attached schematic, which works fine. On the way, I thought I had it worked out with an 8v battery, but the off current went way up when I tried 9 volts.

I figure the "off" current (according to Fluke) is between .1 and 1.4 uA, depending on the battery, which seems acceptable. Most of the "leak" is through the bias resistor.

AMay