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'[PIC]: Power handling for a sleeping PIC system'
2002\10\14@112314 by Anand Dhuru

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HI Folks,

I am designing a PIC based security device, where the transmitter would be asleep most of the time. It would wake up every minute or so, send a burst, and go back to sleep mode. Since the data to be transmitted is minimal, and no complex computing involved, I am planning to run the PIC at 32 KHz to conserve the battery.

Now, the problem is the transmitter module requires 5 Volts minimum, which rules out using a 3 volt lithium cell.

If I use a compact 12 V battery, I would have to use a 3 pin regulator or a zener, both of which would consume power even when the PIC is asleep.

What would be the best strategy under the circumstances?

I thought of using 2 lithum cells in series, so that the PIC operates at 3 V, and the transmitter at 6 V; does this make sense?

Or is there a better way to do this?

Thanks and regards,

Anand Dhuru

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2002\10\14@113149 by andy n1yew

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use a 12 v battery and the black regulator

andrew
----- Original Message -----
From: "Anand Dhuru" <spam_OUTardhuruTakeThisOuTspamVSNL.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Monday, October 14, 2002 11:19 AM
Subject: Re: [PIC]: Power handling for a sleeping PIC system


HI Folks,

I am designing a PIC based security device, where the transmitter would be
asleep most of the time. It would wake up every minute or so, send a burst,
and go back to sleep mode. Since the data to be transmitted is minimal, and
no complex computing involved, I am planning to run the PIC at 32 KHz to
conserve the battery.

Now, the problem is the transmitter module requires 5 Volts minimum, which
rules out using a 3 volt lithium cell.

If I use a compact 12 V battery, I would have to use a 3 pin regulator or a
zener, both of which would consume power even when the PIC is asleep.

What would be the best strategy under the circumstances?

I thought of using 2 lithum cells in series, so that the PIC operates at 3
V, and the transmitter at 6 V; does this make sense?

Or is there a better way to do this?

Thanks and regards,

Anand Dhuru

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2002\10\14@113621 by Michael Rigby-Jones

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{Quote hidden}

Run the PIC at 3volts from a lithium cell, and when the PIC wakes up, have
it enable a simple switched capacitor voltage doubler to power the TX.

Regards

Mike

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2002\10\14@122140 by mike

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On Mon, 14 Oct 2002 20:49:09 +0530, you wrote:

>HI Folks,
>
>I am designing a PIC based security device, where the transmitter would be asleep most of the time. It would wake up every minute or so, send a burst, and go back to sleep mode. Since the data to be transmitted is minimal, and no complex computing involved, I am planning to run the PIC at 32 KHz to conserve the battery.
>
>Now, the problem is the transmitter module requires 5 Volts minimum, which rules out using a 3 volt lithium cell.
>
>If I use a compact 12 V battery, I would have to use a 3 pin regulator or a zener, both of which would consume power even when the PIC is asleep.
You could use something like the Holtek HT7150 or ON (Motorola)
78LC50, which take a microamp or so.
You might look at the feasibility of using a charge pump (driven from
a PIC pin) to double a 3V supply.
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2002\10\14@123147 by Marco Genovesi

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Not a g.p. 70L05, but there are some very low power 5V regulator (National
LM2936 and others, Seiko S-812XX family..) with less than 10uA standby
current. However,  the voltage doubler only for the TX isn't a bad idea.

Marco


{Original Message removed}

2002\10\14@131608 by Wagner Lipnharski

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Marco Genovesi wrote:
> Not a g.p. 70L05, but there are some very low power 5V regulator
> (National LM2936 and others, Seiko S-812XX family..) with less than
> 10uA standby current. However,  the voltage doubler only for the TX
> isn't a bad idea.
>
> Marco

If you think about power conversion, nothing converts Voltage better
efficiency than 85 to 90%.
Suppose the processor consumes 5mA @ 3V, and the transmitter consumes 20mA
@ 5V.
Converting 3V to 5V at 85% efficiency for 20mA, will drain 5/3 * 0.02 /
0.85 = 40mA, plus the processor's 5mA, total is 45mA from the 3V cell.

Now, the same processor running at 5V can drain probably 8 to 10mA.
Suppose you tie up all to 4 NiMH cells (4.8V), it will drain 28 to 30mA
from the batteries. It means 33% less power consume than the 3V and step up
conversion solution.

Now, if you use 2 simple 1N4004 diodes in series with the VCC to the
processor, it probably will reduce current consume to 6 to 7mA, total
consume to 26 to 27mA.

The point here, is that the processor can reduce its current consume based
on the voltage supplied as VCC, and the 15% loss in conversion can justify
to use a 4.8V battery pack instead of 3V cell.

Suppose you use 2 x 3V cells (6V), even using 1 diode to drop a bit the VCC
to the transmitter, and 3 diodes to drop the VCC to the processor, you
probably will have half the consume from the step up solution.  But either
way, two cells, twice the energy autonomy, so, no much gain.  This,
considering a high efficiency of 85%, capacitive charge pumps does have
numbers worse than that.

The thing to observe; Is the processor able to drive the transmitter with
its logic up to 3V while the transmitter is tied to 5V ?

Wagner Lipnharski - email:  EraseMEwagnerspam_OUTspamTakeThisOuTustr.net
UST Research Inc. - Development Director
http://www.ustr.net - Orlando Florida 32837
Licensed Consultant Atmel AVR _/_/_/_/_/_/

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2002\10\14@134044 by Roman Black

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andy n1yew wrote:
>
> use a 12 v battery and the black regulator

> ----- Original Message -----
> I am designing a PIC based security device, where the transmitter would be
> asleep most of the time.
> Now, the problem is the transmitter module requires 5 Volts minimum, which
> rules out using a 3 volt lithium cell.
> If I use a compact 12 V battery, I would have to use a 3 pin regulator or a
> zener, both of which would consume power even when the PIC is asleep.


Yep that would be my choice too! ;o)
I did test the Black regulator to be usable
with a 220k zener resistor (and 12v in 5v out),
and in zero-load condition that is the only part
drawing current which is about 30uA. The good
news is that you will get around 2x current
gain when the PIC and transmitter are operating,
giving much improved battery life.

Obviously the PIC will continue drawing some
current even when asleep and there will be some
leakage in the filter cap.

I *think* it may be possible to reduce that
quiescent current from the 30uA to close to 0uA
by adding another transistor in the zener circuit
which disables the zener under no-load condition.

Some possible problems using the regulator for
such small loads are the requirement for high gain
transistor and the fact that the SMPS regulator
will go linear with very low loads. If the PIC
only draws a couple of mA when running it will
probably be linear. If the PIC+transmitter etc
are 20mA or more it should be running in SMPS mode.
-Roman

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2002\10\14@141043 by Anand Dhuru

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Thanks for the great suggestions, guys.

> Suppose you use 2 x 3V cells (6V), even using 1 diode to drop a bit the
VCC
> to the transmitter, and 3 diodes to drop the VCC to the processor, you

No, Wagner, I think you misunderstood this. The 2 cells are in series; the
negative is treated as ground, positive of the first (3V) as VCC for the
PIC, and positive of the second cell (6V with respect to gnd) powers the
transmitter. This way, I dont have to use a 3 pin regulator at all. The PIC
gets 3V, and the transmitter 6V. Of course, the PIC cell would always run
out faster than the other, as it effectively powers both, the PIC AND the
transmitter.

Anyway, I think the idea of using a charge pump is far more elegant than
mine. Especially since the PIC is a 16F628; I can use the hardware PWM,
right?

In which case, what might be a good value for the frequency? And would it be
asking for too much, if someone has a schematic with component values?

> The thing to observe; Is the processor able to drive the transmitter with
> its logic up to 3V while the transmitter is tied to 5V ?

Another potential problem I expect to come up! I am planning on powering up
the transmitter from the PIC thru' a transistor, and then, after a short
delay, use another bit on the PIC to send data.  Hope it works the way I
think it should!

Regards,

Anand Dhuru


{Quote hidden}

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2002\10\14@161651 by Wagner Lipnharski

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Anand Dhuru wrote:
{Quote hidden}

This can give you some ideas. Performance is horrible, and if switching
time is slow the transistors will collapse.
Much better designs can be done. Perhaps the use of a commercial charge
pump or even a coilled step up system, check the very low cost MC34063.


        3VCC
         o
         |   D        D      Vout <+5.5V
   .-----o--->|---o--->|---o------>
   |     |        |        |
   R     |        |        |
   |     E        |+       |+
   o---B PNP     ===      ===
   |     C       ---      ---
   R     |        |        |
   |     |        |        |
o---o     o--------'       _|_
   |     |
   R     |
   |     C
   o---B NPN
   |     E
   R     |
   |     |
   '-----o
         |
        _|_
{Quote hidden}

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2002\10\14@172433 by mike

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On Mon, 14 Oct 2002 13:13:13 -0400, you wrote:

>Marco Genovesi wrote:
>> Not a g.p. 70L05, but there are some very low power 5V regulator
>> (National LM2936 and others, Seiko S-812XX family..) with less than
>> 10uA standby current. However,  the voltage doubler only for the TX
>> isn't a bad idea.
>>
>> Marco
>
>If you think about power conversion, nothing converts Voltage better
>efficiency than 85 to 90%.
But this problem is not about efficiency, it's about standby power
consumption. As this product will be asleep most of the time, active power draw
only contributes a small amount to the total battery drain, so
regulator efficiency at higher currents is not a major issue - it's
the quiescent current that's critical.

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2002\10\14@172641 by mike

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On Tue, 15 Oct 2002 03:34:08 +1000, you wrote:

>andy n1yew wrote:
>>
>> use a 12 v battery and the black regulator
>
>> {Original Message removed}

2002\10\14@172847 by mike

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On Mon, 14 Oct 2002 23:35:38 +0530, you wrote:

>Thanks for the great suggestions, guys.
>
>> Suppose you use 2 x 3V cells (6V), even using 1 diode to drop a bit the
>VCC
>> to the transmitter, and 3 diodes to drop the VCC to the processor, you
>
>No, Wagner, I think you misunderstood this. The 2 cells are in series; the
>negative is treated as ground, positive of the first (3V) as VCC for the
>PIC, and positive of the second cell (6V with respect to gnd) powers the
>transmitter. This way, I dont have to use a 3 pin regulator at all. The PIC
>gets 3V, and the transmitter 6V. Of course, the PIC cell would always run
>out faster than the other, as it effectively powers both, the PIC AND the
>transmitter.
>
>Anyway, I think the idea of using a charge pump is far more elegant than
>mine. Especially since the PIC is a 16F628; I can use the hardware PWM,
>right?
>
>In which case, what might be a good value for the frequency? As high as possiblr, to reduce the size of filter caps needed. May be
tricky at 32KHz clock
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2002\10\14@173725 by Peter L. Peres

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On Mon, 14 Oct 2002, Anand Dhuru wrote:

*>HI Folks,
*>
*>I am designing a PIC based security device, where the transmitter would
*>be asleep most of the time. It would wake up every minute or so, send a
*>burst, and go back to sleep mode. Since the data to be transmitted is
*>minimal, and no complex computing involved, I am planning to run the PIC
*>at 32 KHz to conserve the battery.

Use a dc/dc converter or use a PIC output pin (or pins, in parallel) to
form a charge pump that (almost) doubles the voltage.

Peter

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2002\10\15@031226 by Michael Rigby-Jones

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> -----Original Message-----
> From: Anand Dhuru [SMTP:@spam@ardhuruKILLspamspamVSNL.COM]
> Sent: Monday, October 14, 2002 7:06 PM
> To:   KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [PIC]: Power handling for a sleeping PIC system
>
> Anyway, I think the idea of using a charge pump is far more elegant than
> mine. Especially since the PIC is a 16F628; I can use the hardware PWM,
> right?
>
> In which case, what might be a good value for the frequency? And would it
> be
> asking for too much, if someone has a schematic with component values?
>
You could use the PIC's PWM with a couple of diodes and capacitors to
provide the doubling.  For minium ripple, you want the frequency as high as
possible which means setting up the PWM for as low resolution as possible.
If you take a look at http://www.reconnsworld.com/power_voltdoubler.html it
shows a voltage doubler connected to the output of a 555 timer, this would
be exactly the same if you were using the PIC's PWM output.

If you need more current or less ripple or both, then consider one of the
pre-packaged charge pumps made by e.g. Maxim.  The MAX5008 will produce
5volts from a 3v lithium cell with a maximum output current of 140mA, more
than enough for you application I hope!  It also runs at 1MHz allowing the
use of small ceramic caps, and has a shutdown current consumption of 0.1uA.
Only available in surface mount, and a very tiny package at that (uMAX), but
other vendors make similar products.

Regards

Mike

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2002\10\16@004353 by Anand Dhuru

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Michael, thanks for all the help, and specifically for pointing me to the
URL with the voltage doubler.

Regards,

Anand Dhuru

----- Original Message -----
From: "Michael Rigby-Jones" <RemoveMEmrjonesTakeThisOuTspamNORTELNETWORKS.COM>
To: <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Tuesday, October 15, 2002 12:41 PM
Subject: Re: [PIC]: Power handling for a sleeping PIC system


> > {Original Message removed}

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