piclist 2001\01\22\181705a >
Thread: Auto-off circuit?
face BY : mike@whitewing.co.uk

On Mon, 22 Jan 2001 19:51:07 -0800, you wrote:

>I am looking for a circuit that I can implement that will allow a pic to
>turn itself off. I have tried going into sleep mode after a timer time-out,
>but the battery drain is still too much.
>I would like to power up using a momentary push button switch.
>By the way, in sleep mode, my 16f8xx is drawing over 1mA, even after
>following the suggested procedures to minimize drain.
In that case something is very wrong - you are probably sourcing or
sinking current somewhere unintended. Sleep mode current should be
under 20uA with the WDT on.
>I want to power the pic from a 9volt transistor radio battery. I am using a
>78L05 regulator. Are there any regulators that have a shut down option?
The 78L05 has very high quiescent current (>1mA), and not suitable for
'always-on' apps. Is this the 1mA mentioned above maybe ?
Look at devices like the Ricoh RN5RL50AA, Motorola 78LC and FC series,
as well as similar devices from Telcom and Seiko. These have quiescent
currents of a couple of microamps.  The Nat. Semi LP2950 is more easily obtainable, but draws
significantly more current than the above devices.

There is no need to mess with turning the PIC power off - a properly
designed PIC circuit with the right regulator can be made to draw
sufficiently low current in sleep that battery shelf life is more of
an issue with a 9V battery.  
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<lt1p6tk02s10f732ael7ssjolkvagmkt8b@4ax.com> quoted-printable

In reply to: <20010122154958.B03F6B6@bifur.cmc.net>
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