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'Low current power for a PIC'
1999\10\15@102950 by Chris Eddy

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Associates;

I have a PIC that must live off of a 220uF cap for 7 seconds.  I can get
the PIC to consume low power, but I am having trouble getting the
regulator designed.  The 78L05 sucks 2-3mA Q current, way too much.
Looking for 50-100uA.  The low dropout regs are neat, but they have a
very limitted Vin max.  I need 30V.  I built a pass regulator with a
res, zener, and NPN trans, which meets my goals, but since the current
through the zener is low, then as the V on the C drops off, then the V
on the zener drops off, and the V on the PIC droops as well.  This
causes the RC osc to skew, and my highly important timer gives me
predictable garbage!

Any great ideas?

Chris Eddy
Pioneer Microsystems, Inc.

1999\10\15@110101 by Jim Hartmann

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A couple of ideas:
1. Use a  pre-regulator to a low drop out regulator to get the Vin low
enough.
2. Use LP mode xtal oscillator to lower operating current.






Chris Eddy <spam_OUTceddyTakeThisOuTspamNB.NET>TakeThisOuTspamMITVMA.MIT.EDU> on 10/15/1999 09:30:18 AM

Please respond to pic microcontroller discussion list
     <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>

Sent by:  pic microcontroller discussion list <PICLISTspamKILLspamMITVMA.MIT.EDU>


To:   .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
cc:
Subject:  Low current power for a PIC


Associates;

I have a PIC that must live off of a 220uF cap for 7 seconds.  I can get
the PIC to consume low power, but I am having trouble getting the
regulator designed.  The 78L05 sucks 2-3mA Q current, way too much.
Looking for 50-100uA.  The low dropout regs are neat, but they have a
very limitted Vin max.  I need 30V.  I built a pass regulator with a
res, zener, and NPN trans, which meets my goals, but since the current
through the zener is low, then as the V on the C drops off, then the V
on the zener drops off, and the V on the PIC droops as well.  This
causes the RC osc to skew, and my highly important timer gives me
predictable garbage!

Any great ideas?

Chris Eddy
Pioneer Microsystems, Inc.

1999\10\15@111142 by Scott Newell

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>regulator designed.  The 78L05 sucks 2-3mA Q current, way too much.
>Looking for 50-100uA.  The low dropout regs are neat, but they have a
>very limitted Vin max.  I need 30V.  I built a pass regulator with a

I'm using some of the old National LDOs (LM2941).  They can take the
voltage, but the quiescent current is way more than 5ma!


>res, zener, and NPN trans, which meets my goals, but since the current
>through the zener is low, then as the V on the C drops off, then the V
>on the zener drops off, and the V on the PIC droops as well.  This
>causes the RC osc to skew, and my highly important timer gives me
>predictable garbage!

Low voltage and current starved zeners suck.

I've used series (REF-02) voltage references for precision low current
regulators in the past.  You might look into replacing the zener with a
micropower shunt regulator (bandgap ref) that will regulate much better at
low currents (10 uA).

Check out LM385 (shunt) and LM2936 (series).


newell

1999\10\15@112549 by Thomas C. Sefranek

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Chris Eddy wrote:

> Associates;
>
> I have a PIC that must live off of a 220uF cap for 7 seconds.  I can get
> the PIC to consume low power,

O.K.  What is the current the PIC consumes?

> but I am having trouble getting the
> regulator designed.  The 78L05 sucks 2-3mA Q current, way too much.
> Looking for 50-100uA.

Do you mean you can stand a regulator burden of 100 ua?

> The low dropout regs are neat, but they have a
> very limitted Vin max.  I need 30V.  I built a pass regulator with a
> res, zener, and NPN trans, which meets my goals, but since the current
> through the zener is low, then as the V on the C drops off, then the V
> on the zener drops off, and the V on the PIC droops as well.  This
> causes the RC osc to skew, and my highly important timer gives me
> predictable garbage!
>
> Any great ideas?

Yes, but I need more info.

>
>
> Chris Eddy
> Pioneer Microsystems, Inc.

--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html

1999\10\15@112749 by Alan Pearce

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>I've used series (REF-02) voltage references for precision low current
>regulators in the past.  You might look into replacing the zener with a
>micropower shunt regulator (bandgap ref) that will regulate much better at
>low currents (10 uA).

The above idea is pretty good, and may be better than mine, which was to
investigate the micropower chips used in cellphones. If I remember correctly
Maxim make micropower regulators for this use, but I doubt they will have the
input voltage requirement you want.

1999\10\15@114205 by Geier, David

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Hello

Check out the Infineon TLE 4264 G.  45V input voltage.  400ua max current
consumption.  It is also very well protected against short and reverse
voltage.  It comes in a SOT223.  Infineon has a whole family of related
parts in different packages.

David Geier
Spectra Precision

{Original Message removed}

1999\10\15@115308 by Ray Gardiner

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<x-flowed>You could use a LP2950 which will give you 100uA quiescent
and a series zener to drop the volts to below 30.

If you need REALLY low quiescent current check the Seiko S-812XXPG series
1.2uA to 3.2uA max, unfortunately Vin(max) is 16 Volts :-(







Ray Gardiner EraseMErayspam_OUTspamTakeThisOuTdsp.com.au

</x-flowed>

1999\10\15@120057 by Craig Lee

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The LM2936 from National Semiconductor is exactly what you need.

40V max in 5V@50mA out  0.2V dropout 9uA quiescent  $1.22 US.

Craig

> {Original Message removed}

1999\10\15@174907 by William K. Borsum

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At 10:08 AM 10/15/99 -0500, you wrote:
{Quote hidden}

Another one to look at are the MAX 666 series, and the pin equivalent but
better Analog devices 666 series.  Also for precision and low power, we use
the REF19x series.

Kelly

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<borsumspamspam_OUTdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\10\15@213450 by Chris Eddy

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Thanks for the regulator suggestions.. I am hunting down each idea suggested.

Chris Eddy

1999\10\15@234642 by Mark Willis

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Ray Gardiner wrote:
>
> You could use a LP2950 which will give you 100uA quiescent
> and a series zener to drop the volts to below 30.
>
> If you need REALLY low quiescent current check the Seiko S-812XXPG series
> 1.2uA to 3.2uA max, unfortunately Vin(max) is 16 Volts :-(
>
> Ray Gardiner @spam@rayKILLspamspamdsp.com.au

Thought: use a "gold cap" or the like, with higher capacitance but same
size footprint as your current capacitor, with an LDO regulator?  If
your LDO regulators don't like high voltage, feed them more capacitance
on the input filter <G>

 Mark

1999\10\16@055213 by Dr. Imre Bartfai

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Hi,

maybe I will say bullshit. But I think two things:

1. Use XTAL instead or RC
2. Use PIC with built-in brown-out detector or apply an external one. If
the voltage on the PIC drops, the cap approaches the empty state so it is
safer turn the whole device off at this moment. This is done by BOD.

I hope this helps.

Imre


On Fri, 15 Oct 1999, Chris Eddy wrote:

{Quote hidden}

1999\10\16@071759 by Russell McMahon

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Chris,

I think a nearly perfect "plug it in and go" solution for your stated
problem (gotta cover my bases ;-)) is the Nat Semi LM2936 regulator.
This offers -

   40 volt maximum input

   15uA worst case quiescent current for 100uA load  (9uA typical)
   Rising to 200/500uA at 10mA load.
   I have found that the actual quiescent current seems to be better than
this.

   Dropout voltage is 5.5 volts

   Standard pinout.
   Std 3 pin TO92 or 8 pin SO pkg

The only real limitation of these compared to "normal" regulators is the
50mA max Iout, which probably won't be a problem in your application.
Somewhat dearer than 78L05 but may not be an issue in your application.

I use the 5 volt version but I believe a 3v version MAY be available.


Lets see, for 1 volt drop in 7 seconds on 220uF current drain is about
I = 220/E6 x 1/7 ~= 30uA.
This means you will get 1 volt of droop over 7 seconds for every 30uA of
load current.or so.
This is rough but indicative.
As you seem to have 30 volts in I guess you can droop from 30v to say 6
volts = 24 volts so load could be 30uA * 24  ~= 750uA.
Should be ample for a lowish powered PIC circuit.

Are there more details which make this not work?


regards,



     Russell McMahon
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What can one man* do?
Help the hungry at no cost to yourself!
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(* - or woman, child or internet enabled intelligent entity :-))


{Original Message removed}

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