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'[EE]: Auto-off circuit?'
2001\01\22@104930 by John Pearson

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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.

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?

Thanks

John

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2001\01\22@105708 by Stephen B Webb

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> By the way, in sleep mode, my 16f8xx is drawing over 1mA, even after
> following the suggested procedures to minimize drain.

Are you sure the PIC is drawing this current?  Maybe the regulator?

Could you instead use 3 AA batteries, and hence no regulator..?

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2001\01\22@105935 by M. Adam Davis

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We just had this discussion (quite a long thread, actually) about a week
ago.  You'll get much better response if you check the archives.

-Adam

John Pearson wrote:
{Quote hidden}

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2001\01\22@121035 by Dan Michaels

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At 07:51 PM 1/22/01 -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.
>
>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?
>

It's your regulator, Icc ~2ma. Try LM2936, LM2950, or Seiko 81250SGY
[avail digikey/mouser].

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2001\01\22@134655 by Dan Michaels

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>
>It's your regulator, Icc ~2ma. Try LM2936, LM2950, or Seiko 81250SGY
>[avail digikey/mouser].
>

Oops, LP2950. Also Seiko 81350HG.

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2001\01\22@181705 by mike

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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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2001\01\23@084123 by Mark Peterson

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I have minimized quiescent current draw by using National Semiconductor's
LM2936Z-5.0N ultra low power regulator.  Also, turning off the brownout
detect configuration bit substantially lowered the current demand.

Mark P



{Quote hidden}

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2001\01\23@175759 by Peter L. Peres

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There are regulators with power off options but there is a hen-or-egg
problem with this. Please search the piclist archive for this. I have
recently posted a circuit that solves your problem (as a pdf attachment).

Peter

PS: The thread subject was: [PIC]: EE challenge PIC && 12V battery

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2001\01\23@192611 by Russell McMahon

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>I have minimized quiescent current draw by using National Semiconductor's
>LM2936Z-5.0N ultra low power regulator.  Also, turning off the brownout
>detect configuration bit substantially lowered the current demand.



The LM2936 is my favourite regulator for micropower applications. Sadly it's
a little expensive.
However, for REALLY low quiescent current requirements it is still not good
enough - about 10 to 20 uA quiescent in pracfice AFAIR.
My power down circuit is over 100 times lower powered :-).
Of course it has the minor disadvantage of having absolutely no power
available  in off mode :-).

As a guide to when this gets important. there are 8766 hours in a year.
A 10 uA drain uses 87660 uA hrs / year or about 88 mAH.
That's a small "13" size  button cell based battery pack depending on the
chemistry used).
Or about 5% of an Alkaline AA cell.
In the latter case the loss is probably inconsequential.
In the case of the coin cell it depends on what you want your battery life
to be and how much energy you take when powered up.


   Russell McMahon

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