Olin,

I'm not necessarily looking for a PIC solution-I cannot program them, so a
PIC solution is a long shot for me.

My question was simple enough I think without the need for a formal
specification with narrow parameters. Stated another way........

If I use an RC circuit (1 meg ohm and 100 uF) for timing and a comparator
with built in reference voltage (2V), am I am I violating the maximum input
specs if I yank the power away from the chip while the IN- comparator input
is still at 2V?

The specs for my device say the inputs should never be more than .3v above
the Vcc or .3v below ground. This was my primary concern. Please disregard
the application information given previously-it just complicates the issue
without addressing my primary question.

TY.

T



On Mon, Aug 18, 2008 at 9:54 AM, Olin Lathrop <olin_piclist@embedinc.com>wrote:

> Artie Jones wrote:
> > I need a cheap battery saver circuit. This is for legacy
> > electronics-it shuts the appliance off if the user forgets to-which
> > prevents the battery from draining if the user forgets to turn the
> > power switch off.
> >
> > ...
> >
> > If anyone knows of a better circuit that does not require an
> > additional switch (uses the stock power switch),
>
> Of course there has to be something beyond the power switch, unless this
> switch can be electrically tripped to off.  Something has to interrupt the
> power if the users leaves the switch on.
>
> > and needs to consume zero power when the auto shut off activates.
>
> Learn how to write specs.  If you truly mean zero power, then forget about
> it.  Quit now.  Go home.  Nothing draws zero power.  There is always some
> leakage.  Real engineers understand there is a "good enough" level for
> everything.  For starters, what is the self-discharge current of your
> battery?
>
> > The circuit can consume a few ma
> > while the device is powered up. And, it should run on 9 volts
>
> OK.
>
> > (or higher) non regulated power.
>
> Go home and write a real spec.  "Or higher" is totally rediculous.  How can
> anyone advise you on a circuit when they have no idea whether it might need
> to withstand 100V, 1000V, or more?
>
> If it turns out the power source is one of those common 9V batteries with
> clip on leads, then the answer might be a 10F200 with a P channel mosfet
> and
> a few other parts.  However, it's pointless to get into this too far
> without
> a spec.
>
>
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