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'[PICLIST] [PIC] 2 X 3VDC bat with PIC'
2001\08\23@124339 by Giles Honeycutt

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How well does a PIC rated at 5.5VDC work with a little over 6 VDC on them?
I can use a diode to drop it down (0.7vdc) a little, but I want it to
operate over as much of the batteries life as possible.

Any suggestions or experience on this?
A low fallout on the PICs may be acceptable.

Best regards,
Giles



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2001\08\23@133005 by Dan Michaels

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At 11:42 AM 8/23/01 -0500, you wrote:
>How well does a PIC rated at 5.5VDC work with a little over 6 VDC on them?
>I can use a diode to drop it down (0.7vdc) a little, but I want it to
>operate over as much of the batteries life as possible.
>
>Any suggestions or experience on this?
>A low fallout on the PICs may be acceptable.
>


Giles, if 6v is critical, you can go with the older PICs - pre-flash,
as they handle a wider Vcc range. I am assuming you are not using
an LDO regulator in the ckt, but rather running directly off your
battery. Personally, I think I would go with a regulator.

- dan
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2001\08\23@133555 by Douglas Butler

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As microcontrollers go, PICs have a wide range of supply voltage.  But
the place to look is at the datasheet.  A commercial 16C54 runs from
3.0V to 5.5V.  Your 6+V battery minus a diode gives you 5.3+V at the
start of life, and the PIC should run till the battery is 3.0 + 0.7 =
3.7V  That should be almost all the life of an alkaline battery.  We
generally consider alkalines dead at 1V/cell.

Sherpa Doug

> {Original Message removed}

2001\08\23@134009 by mike

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On Thu, 23 Aug 2001 11:42:39 -0500, you wrote:

>How well does a PIC rated at 5.5VDC work with a little over 6 VDC on them?
>I can use a diode to drop it down (0.7vdc) a little, but I want it to
>operate over as much of the batteries life as possible.
>
>Any suggestions or experience on this?
>A low fallout on the PICs may be acceptable.
>
>Best regards,
>Giles
If you're talking coin cells, think about using 3 x alkalines instead
of 2x lithiums - LR44's etc. are extremely cheap if you know where to
go (<10 cents).

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2001\08\24@082510 by Giles Honeycutt

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Dan,
I did not want to use a Low Dropout regulator due to the loss of voltage.  I
have not looked in a couple of years, but I think the best on the market
still takes away 1.1 VDC.  I may go to a regulator in the future, as someone
may want to "hotwire" the product with a 9V battery.
I am continuing with a diode in series of the PIC's power supply.  Filter
cap is on the PIC side of the diode.
Best regards,
Giles

>
>Giles, if 6v is critical, you can go with the older PICs - pre-flash,
>as they handle a wider Vcc range. I am assuming you are not using
>an LDO regulator in the ckt, but rather running directly off your
>battery. Personally, I think I would go with a regulator.
>
>- dan


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2001\08\24@084130 by Roman Black

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Giles Honeycutt wrote:
>
> Dan,
> I did not want to use a Low Dropout regulator due to the loss of voltage.  I
> have not looked in a couple of years, but I think the best on the market
> still takes away 1.1 VDC.  I may go to a regulator in the future, as someone
> may want to "hotwire" the product with a 9V battery.
> I am continuing with a diode in series of the PIC's power supply.  Filter
> cap is on the PIC side of the diode.
> Best regards,
> Giles


Giles, I don't think this is correct, the last
low volts dropout 5v regulator I tested regulated
almost perfectly down to 5.0v, then under that
the output voltage mimicked the input voltage.
VERY impressive. It was a small load, 100mA I
think, and the TO-220 regulator. Test one, you
might be pleasantly surprised.
:o)
-Roman

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2001\08\24@090549 by Jinx

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> Dan,
> I did not want to use a Low Dropout regulator due to the
> loss of voltage.  I have not looked in a couple of years,
> but I think the best on the market still takes away 1.1 VDC

I use either the Seiko S81250 or the Nat Semi LP2951.
Both have a dropout between 0.04V and 0.350V (depending
on load), up to 12V input and quiescent current around 50 -
70uA. Easy to get, cheap, good for battery supplies like 6V
gel cells

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2001\08\24@102742 by Herbert Graf

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Have you considered a resiter and zener diode? Say a 5.1V one. That way you
get the best of both worlds, the zener keeps the voltage at 5.1V as long as
the input is about 5.1V, if it drops then the Zener does nothing and your
PIC will continue to function until the voltage is to low for it. TTYL

> {Original Message removed}

2001\08\24@111545 by Giles Honeycutt

picon face
Hmm, I am looking at the LP2980, thanks for the tip.  I notice it has a lot
more current draw than a sleeping PIC.  I guess I will do a little math and
see how long a few uAmps will last on my tiny batteries.

Best regards,
Giles

>I use either the Seiko S81250 or the Nat Semi LP2951.
>Both have a dropout between 0.04V and 0.350V (depending
>on load), up to 12V input and quiescent current around 50 -
>70uA. Easy to get, cheap, good for battery supplies like 6V
>gel cells
>


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2001\08\24@112316 by Giles Honeycutt

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I think useing a zener would hurt over all battery life.  It would pull down
and drain durring shelf life.  I need low current draw durring sleep mode.
Best regards,
Giles


>Have you considered a resiter and zener diode? Say a 5.1V one. That way you
>get the best of both worlds, the zener keeps the voltage at 5.1V as long as
>the input is about 5.1V, if it drops then the Zener does nothing and your
>PIC will continue to function until the voltage is to low for it. TTYL


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2001\08\24@132417 by Andrew E. Kalman

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Re:

>I did not want to use a Low Dropout regulator due to the loss of voltage.  I
>have not looked in a couple of years, but I think the best on the market
>still takes away 1.1 VDC.  I may go to a regulator in the future, as someone
>may want to "hotwire" the product with a 9V battery.
>I am continuing with a diode in series of the PIC's power supply.  Filter
>cap is on the PIC side of the diode.
>Best regards,


FYI, there's a design on our website in App Note AN-6 that has a
PIC12C509A running off either 3xAA (4.5V) or external 6-26Vdc. It
uses an LM2941 regulator on the unregulated DC mainly for low dropout
and reverse-hookup protection.

The kicker in getting it to work in this environment was to put a
diode in series with the output of the regulator -- this blocked the
massive (10mA) drain on the battery side of things when there was no
external input to the regulator. Also,  the battery ground is lifted
when external power is applied. With that series diode, the current
drain from the batteries in sleep mode is what you'd expect from the
PIC alone.  I have a couple of these little Fan Controllers still
running on their original batteries, which were installed in April
2001.

Another nice thing about this scheme is that the nominal voltage when
running from external supplies is very close to that of a set of new
batteries (around 4.4V).

Anyway, this may give you some ideas ...
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2001\08\24@141556 by Giles Honeycutt

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Andrew,
Thanks for the suggestion.  I looked at your app note.  On your appnote the
battery is not regulated at all.  The regulator is for outside power only.
On my application, I only have battery power.  My delima is how to get full
use of 2X3VDC = 6VDC with a PIC that specs 5.5VDC max.
I have recently been looking at LDO regulators as per suggestions on the
list.  They consume a small amount of power when on.  Some have a turn-off
input that makes it almost no current.  This interests me, but I have not
found a low part count way to have a PIC turn its self off using this and
able to wake from sleep.

This has become much to complicated.  A diode off the battery is what I am
using for now.

Best regards,
Giles



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2001\08\24@143509 by Matt Pobursky

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Giles,

Take a look at TI's TPS line of low dropout, low quiescent current linear
regulators. The TPS line in particular is very efficient, quite low cost for
the performance, and generally availability is very good.

I've used a bunch of them for handheld battery powered devices in real products
and had no problems with them. The TPS76950 might fit your application very
well.

http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=TPS76950

If not, TI has a BUNCH of very good alternatives with various packages, output
currents, output voltages and quiescent currents.

Good luck. You should be able to get a standby current of 20uA or less with a
good low dropout micropower regulator. Make sure you read the applications
information and follow their circuit layout guidelines too!

Matt Pobursky
Maximum Performance Systems

On Fri, 24 Aug 2001 10:13:45 -0500, Giles Honeycutt wrote:
{Quote hidden}

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2001\08\24@150809 by Andrew E. Kalman

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Re:

>This has become much to complicated.  A diode off the battery is what I am
>using for now.

Yep, that will be the simplest way to go.  Unfortunately it has no
overvoltage or reverse hookup protection, but I think that's a
reasonable restriction.

I was going to suggest a simple diode in series as a solution to your
problem, but the "hotwire" reference had me worried.

Good Luck! Simple is good.
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2001\08\24@151219 by M. Adam Davis

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If you really want it to operate over as much of the battery life as
possible, you ought to look at 3.3v switching regulators.  Depending on
your current draw, you can find some that require only a capacitor and
the regulator (though the regulator might cost more than a few cents...)

At the same frequency, a PIC will consume less power at 3.3v than at 5v,
furthermore, you'll be throwing less current away using a SMPS than
using a zener or linear regulator.

The only reason *not* to go with smps is for prohibitive costs, but you
can implement a simple smps for less than 50 cents (volume) if that's
not out of your range.

-Adam

Giles Honeycutt wrote:

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2001\08\25@062904 by Peter L. Peres

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> I did not want to use a Low Dropout regulator due to the loss of
> voltage. I have not looked in a couple of years, but I think the best
> on the market still takes away 1.1 VDC.  I may go to a regulator in
> the future, as someone

LDOs with 0.5 to 0.7 V are common. See the Seiko line (also carried by
Digi-Key).

I very often use 4 pill cells and a Si diode to power PICs in keyfobs and
other such small devices, without a regulator.

Peter

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2001\08\25@115453 by Dan Michaels

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Captain.J wrote:
>> Dan,
>> I did not want to use a Low Dropout regulator due to the
>> loss of voltage.  I have not looked in a couple of years,
>> but I think the best on the market still takes away 1.1 VDC
>
>I use either the Seiko S81250 or the Nat Semi LP2951.
>Both have a dropout between 0.04V and 0.350V (depending
>on load), up to 12V input and quiescent current around 50 -
>70uA. Easy to get, cheap, good for battery supplies like 6V
>gel cells
>

Giles,

Also check the LM2936 - dropout volt ~0.2v and 9uA quiesecent
current - great for low-power systems.

- dan
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