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'Reverse Polarity Protection for 3V PIC Circuit.'
1999\05\30@200144 by Peter Homann

picon face
Hi,

I need to protect my PIC16LF84 against reverse polarity. Currently I'm
running the circuit of 2 x 1.5 N cells (2/3 AAA). I want to protect the
circuitry from the batteries being inserted the wrong way.

I'm not keen to put a diode in series with the batteries as I'll loose 0.6V.

Thanks,

Peter.
---
Peter Homann    Email:  spam_OUTpeterhTakeThisOuTspamadacel.com.au
Adacel Technologies Ltd _/_/_/ _/_/_/ _/ Phone:   +61 3 9596 2991
250 Bay St, Brighton   _/  _/   _/   _/  Fax:     +61 3 9596 2960
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1999\05\30@202045 by Dennis Plunkett

flavicon
face
At 10:20 31/05/99 +1000, you wrote:
{Quote hidden}

It depends on quite a few things, as to what can be done.
A shky diode in series will only give you 0.2V drop.
If the current is very low, then even a silicon diode will not give the
full 0.6V.
On a low current circuit a simple series resistor may suffice
A diode accross the battery pack may be better as a simple 1 Ampere shky
will do the job

Dennis

1999\05\30@202052 by Jamil J. Weatherbee

flavicon
face
Since there are only 2 cells you might be able to do this mechanically.
By having a raised ridge around the positive terminal, that only fits the
positive terminal and would be open circuit it the battery near the
positive terminal was inserted backwards.

On Mon, 31 May 1999, Peter Homann wrote:

{Quote hidden}

1999\05\30@202305 by Peter van Hoof

flavicon
face
you could try to find some kind of transistor gizmo to reduce the .6 volt
loss but you would always lose at least the saturation voltage of it.

The better way to go about this is to protect reversal based on the
mechanical properties of the battery. mostly this is done by a positive
battery terminal that is set back in the holder so only the positive battery
pole that sticks out can reach it. look in remote controlls that's where you
see this most of the time

Peter .....pvhKILLspamspam.....vertonet.com

{Original Message removed}

1999\05\30@202308 by David Covick

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face
Peter,

You can take an enhancement power MOSFET and put in the negative return
line from your circuit. The gate is driven through a 1 Meg resistor from the
positive supply terminal. A correct power connection drives the MOSFET fully
ON, and everything works. Reversing the supply connections turns the MOSFET
OFF,
and no current flows and you're protected. Correct the power connections,
and you're back to normal. There is very
little voltage drop across the MOSFET. Select a MOSFET with a low "R(on)"
resistance, and there will be very little voltage drop.

David




{Original Message removed}

1999\05\30@202712 by Jamil J. Weatherbee

flavicon
face
If size/little more power isn't an issue you could use a very small
mechanical relay, with the coil driven by a series rectifier. Kind of
silly but an idea. :)



On Mon, 31 May 1999, Dennis Plunkett wrote:

{Quote hidden}

1999\05\30@203130 by D. F. Welch

picon face
At 10:20 AM 5/31/99 +1000, you wrote:
>Hi,
>
>I need to protect my PIC16LF84 against reverse polarity. Why not put a
diode between VCC & Gnd ( Cathode to VCC)
Since it will be reversed biased normally it won't hurt you
and if the supply is reversed it will conduct.  In fact if
you use a Germanium diode you can clamp the reverse voltage
to 0.3 Volts.


73,
Dan Welch
w6dfwspamspam_OUTqsl.net

1999\05\30@205702 by David Covick

flavicon
face
Peter,

Second thought, the MOSFET may need more gate voltage to turn it on fully.
Typically, one needs 8 volts.  The 5 volt logic MOSFETS may work.....have
not tried it at this low voltage.

David


{Original Message removed}

1999\05\30@222314 by Harold Hallikainen

picon face
       Could use a Schotky diode, which has a lower voltage drop.  Also, you
can put a resistor or PTC thermistor in series with one lead of the
battery, then a diode ACROSS the PIC circuit.
       I just did a 3V PIC circuit that used a TI power amp chip as well.  I
used 3 AA cells with a series Schotky.  This drove the TI audio power amp
directly.  It also went thru a Maxim micropower LDO regulator to drive
the PIC (and ISD voice chip).

Harold


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1999\05\30@225638 by Brent Brown

picon face
Davids suggestion about using a MOSFET for reverse polarity
protection is the best idea by far, but an important thing to note is
that the N-Chanel Enhancement MOSFET is used "upside down"
compared to other circuits.  That is to say, the Drain is connected
to -ve, Source through the load to +ve, and gate to +ve.

When the battery supply is correctly connected the MOSFET is
biased ON and current flows in the forward direction of the inherent
Source-Drain diode in the MOSFET.

With reverse battery supply the MOSFET is OFF and the Source-
Drain diode is blocking.

Should work fine, but use a suitable 3V logic level MOSFET.

Brent


Brent Brown
Electronic Design Solutions &
HI-TECH Software Reseller
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1999\05\30@232430 by Dennis Plunkett

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face
At 14:44 31/05/99 +1200, you wrote:
{Quote hidden}

Yes, but requires 2 components and one of them must be very type specific
i.e. N channel 3V FET. This makes this option not cheep in the production
format.
One diode is cheeper and just as effective, the mechanical means that have
been borught up will only sort of work, as you can almost put money on it
that there will be someone that manages to get the small cells in
backwards. The mechanical means is just another level of protection.

Dennis

1999\05\31@023217 by William K. Borsum

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face
<x-rich>RE the list on using a MOSFET for reverse polarity protection......


Should work fine for <underline>single</underline> power source--I used
the circuit and it works really great--low low voltage drop with the
right part.


QUESTION:  has anyone manage a clever way to do this with MULTIPLE power
sources??  The FET itself will pass current in either direction when it
is on.  I need to run redundant, but isolated power sources into a data
logger--a couple of internal batteries, external batteries, and a
wall-cube power supply in a "highest voltage rules" configuration without
any power being forced into the lower voltage sources.


QUESTION 2: How about leakage when off?  Anyone have any real-world
measurements?


Kelly



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</x-rich>

1999\05\31@123354 by Jim Paul

picon face
You could add a diode across the batteries with a fuse
so that is the batteries are inserted the wrong way, the
fuse blows cutting off the power source.
                          -       +
                 --------:|:|:|--------------------------------->  To PIC
circuitry
                 |      Battery               |
                 |                                 ^
                 |                                ----
                 |                                  |
                 |-----------------------~-------------------->  To PIC
circuitry
                                             Fuse

If the batteries are put in backwards, the diode turns on and
pops the fuse.  Otherwise, the diode is reverse biased, and
doesn't even appear to be there.  I've used this scheme
many times before.  It works well.   Hope it helps you out too.

                                                                   Regards,

                                                                       Jim







{Original Message removed}

1999\05\31@181839 by paulb

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face
Dennis Plunkett wrote:

> Yes, but requires 2 components and one of them must be very type
> specific i.e. N channel 3V FET.  This makes this option not cheep in
> the production format.

 Ha Ha!  Tough luck.  You want the function, you buy the part!  But
what is the other component to which you refer?

> One diode is cheeper and just as effective,

 Anyone have a measured comparison on this?  Schottky versus 3V FET at
various currents including 2µA, 100µA, 1mA, 10mA?

> the mechanical means that have been brought up will only sort of work,
> as you can almost put money on it that there will be someone that
> manages to get the small cells in backwards.  The mechanical means is
> just another level of protection.

 Absolutely!  Thus the products with the lithium cell(s) permanently
soldered in.  You all know the "invent a better idiot" story.
--
 Cheers,
       Paul B.

1999\05\31@182513 by paulb

flavicon
face
Jim Paul wrote:

> You could add a diode across the batteries with a fuse so that is the
> batteries are inserted the wrong way, the fuse blows cutting off the
> power source.

 But then your appliance has "failed".  Not good publicity.  OK, if it
is used under supervision and can be repaired and put back into service.
Better to use a resistor (only need a few ohms) and diode.

 Reverse-inserted batteries promptly go flat.  "Darn batteries!"
Properly inserted ones last for "ages".  Appliance always works if
good batteries inserted correctly.  This is the "teaching" approach.
--
 Cheers,
       Paul B.

1999\05\31@184617 by Jim Paul

picon face
I don't agree with the statement that your product has failed.  Just the
contrary.
The user has preserved his/her investment in that product.  The failure is
in the
user not following instructions in installing the batteries.  If they would
have been
paying attention, they wouldn't have put the batteries in backwards, and
they
would not have had the inconvienence of a blown fuse.  But they only lost a
fuse
and a little time, not the whole unit.

As far as not being servicable by the user, how much education and
coordination
does it take to change a fuse.  It would have taken less time to pay
attention to
the battery installation instructions in the first place, thereby saving
time and trouble.

The end choice is up to the designer.  I only offered a suggestion.  One
that has been
used and proven by me.  It is there for you to consider.  Whether you use it
in your end
product is totally up to you.   Whatever  failsafe method is chosen, as long
as it provides
the degree of safety necessary, and at a cost that is agreeable by everyone
involved, is
the right choice for that product.

I guess I'm done now.   Thanks for letting me sound off on what I think
regarding this issue.


Good Luck,


Jim


{Original Message removed}

1999\05\31@190451 by Sean Breheny

face picon face
Yes, I agree that the resistor is often better, but what if your device
needs to draw a large current periodically, and is not operating at that
much voltage overhead (deriving 5v from 8v using an LDO reg,for example).
Then, I don't think that a large enough resistor to protect the  diode is
practical. I guess the only real choice in these cases (other than the
fuse) is a more sophistocated method,such as the FET.

Sean

At 08:22 AM 6/1/99 +1000, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
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1999\05\31@191535 by Dennis Plunkett

flavicon
face
At 17:49 31/05/99 -0500, you wrote:
>I don't agree with the statement that your product has failed.  Just the
>contrary.

No, the product has failed! A blow fuse is a failure it stops working!
Hence FAILed

>The user has preserved his/her investment in that product.  The failure is
>in the
>user not following instructions in installing the batteries.

There is some argument about service technicians not being able to change a
set of torch batteries without an instructiion manual appicable here, be
dammed if I can remember it :)


> If they would
>have been
>paying attention, they wouldn't have put the batteries in backwards, and
>they
>would not have had the inconvienence of a blown fuse.  But they only lost a
>fuse
>and a little time, not the whole unit.
>

Fuses in battery operated devices (Hand held) since when?


>As far as not being servicable by the user, how much education and
>coordination
>does it take to change a fuse.

An IQ or more than moron level perhaps?

>It would have taken less time to pay
>attention to
>the battery installation instructions in the first place, thereby saving
>time and trouble.
>

If they can get the batteries wrong, then why do you assume that the
operator can get a fuse correct?
What is stopping the operator from changing it to a higher rating say a 3"
nail?


>The end choice is up to the designer.  I only offered a suggestion.  One
>that has been
>used and proven by me.  It is there for you to consider.  Whether you use it
>in your end
>product is totally up to you.


All suggestions are open to comment. Sometimes there may be a better mouse
trap out there, never hurts to check. (Snap!)


>Whatever  failsafe method is chosen, as long
>as it provides
>the degree of safety necessary, and at a cost that is agreeable by everyone
>involved, is
>the right choice for that product.
>

Fuses and fuse holders are expesnsive, yet alone all the abuse that you cop
when a fuse blows (Operator error or not)


Dennis

>I guess I'm done now.   Thanks for letting me sound off on what I think
>regarding this issue.
>
>
>Good Luck,
>
>
>Jim
>
>
>{Original Message removed}

1999\05\31@192403 by Richard Prosser

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What about a polyswitch or a PTC resistor (instead of a fuse or fixed
resistor)
Richard

{Quote hidden}

1999\05\31@193211 by Andy Kunz

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face
>  Reverse-inserted batteries promptly go flat.  "Darn batteries!"
>Properly inserted ones last for "ages".  Appliance always works if
>good batteries inserted correctly.  This is the "teaching" approach.

Why not just power the PIC through it's I/O pins.  If you are dealing with
low current, this works great.

For instance, if RB.0 and RB.1 are your "power" pins (tie MCLR to regular
VCC pin!)

       movf    RB,0
       movwf   RB
       bsf     RP0
       movlw   xxxxxx00
       movwf   RB
       bcf     RP0

This will cause your power rails to be connected about as directly as
possible, and still not have to worry about battery polarity.  If you're
smart about it, you can power your entire circuit _through_ the PIC if you
keep the currents low.

Andy
==================================================================
  Montana Design Tech Support - http://www.montanadesign.com
==================================================================

1999\05\31@204613 by William K. Borsum

flavicon
face
At 11:37 AM 5/31/99 -0500, you wrote:
>You could add a diode across the batteries with a fuse
>so that is the batteries are inserted the wrong way, the
>fuse blows cutting off the power source.
>                           -       +
>                  --------:|:|:|--------------------------------->  To PIC
>circuitry
>                  |      Battery               |
>                  |                                 ^
>                  |                                ----
>                  |                                  |
>                  |-----------------------~-------------------->  To PIC
>circuitry
>                                              Fuse
>
>If the batteries are put in backwards, the diode turns on and
>pops the fuse.  Otherwise, the diode is reverse biased, and
>doesn't even appear to be there.  I've used this scheme
>many times before.  It works well.   Hope it helps you out too.

At a $1 plus per fuse, that can get very expensive when you have idiots
replacing the batteries.

How about replacing the fuse with one of the PTC thermal auto-resetting
devices from Bourns or Littlefuse?
Does anyone have any PRACTICAL experience doing this??  Are they fast
enough with a big overload?

Kelly

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All legitimate attachments to this email will be clearly identified in the
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1999\05\31@214057 by Tony Nixon

flavicon
picon face
Peter Homann wrote:
>
> Hi,
>
> I need to protect my PIC16LF84 against reverse polarity. Currently I'm
> running the circuit of 2 x 1.5 N cells (2/3 AAA). I want to protect the
> circuitry from the batteries being inserted the wrong way.

Just a thought,

I wonder if the PIC will be damaged at all with a 3V reversed battery.

Every protection diode on the IO pins will be conducting between VCC and
GND rails in the chip, thus trying to drop the battery voltage to around
1.2V.

Maybe no damaging current is available to flow into the chips' 'guts'.

Perhaps a simple resistor in series with VCC will suffice to limit this
current.

Maybe this is why I have not damaged 16F84's by inserting them into a
socket the wrong way around.

--
Best regards

Tony

PicNPoke - Multimedia 16F84 Beginners PIC Tools.

http://www.picnpoke.com
Email RemoveMEpicnpokeTakeThisOuTspamspamcdi.com.au

1999\05\31@215548 by David Covick

flavicon
face
Tony,

I just finished a project that uses 4 AA batteries.  At over 6 volts, I
applied the voltage backwards for maybe 2 minutes or more.  I wondered why
my start-up beeps did not sound and just what went wrong.  I checked my
circuitry and found nothing.......I placed my finger on the F84 and it was
very HOT.  I said to myself...hey what's going on here........the battery
pack was backwards (alligator clips).

Bottom line.....what you say has merit.  I never did put in any reverse
polarity protection.  The project is supose to run until the batteries are
depleted and it is a low cost device.  I could not afford a voltage drop.

3 volts would probably have minimal effect, except killing the batteries :)

David


{Original Message removed}

1999\05\31@220028 by Richard Prosser

flavicon
face
But did it work again afterwards????
Richard

{Quote hidden}

1999\05\31@220346 by David Covick

flavicon
face
Yup, It worked fine.  It is still in the prototype and keeps on a tick'n.




----- Original Message -----
From: Richard Prosser <EraseMERPROSSERspamEraseMESWICHTEC.CO.NZ>
To: <@spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU>
Sent: Monday, May 31, 1999 6:58 PM
Subject: Re: Reverse Polarity Protection for 3V PIC Circuit.


> But did it work again afterwards????
> Richard
>
> > {Original Message removed}


'Reverse Polarity Protection for 3V PIC Circuit.'
1999\06\01@000959 by paulb
flavicon
face
Sean Breheny wrote:

> Yes, I agree that the resistor is often better, but what if your
> device needs to draw a large current periodically, and is not
> operating at that much voltage overhead (deriving 5v from 8v using an
> LDO reg,for example).  Then, I don't think that a large enough
> resistor to protect the diode is practical.

 Think: 3V torch globe.
--
 Cheers,
       Paul B.

1999\06\01@010930 by Harold Hallikainen

picon face
On Mon, 31 May 1999 18:54:34 -0700 David Covick <spamBeGonedacspamKILLspamWEST.NET> writes:
>Tony,
>
>I just finished a project that uses 4 AA batteries.  At over 6 volts,
>I
>applied the voltage backwards for maybe 2 minutes or more.  I wondered
>why
>my start-up beeps did not sound and just what went wrong.  I checked
>my
>circuitry and found nothing.......I placed my finger on the F84 and it
>was
>very HOT.  I said to myself...hey what's going on here........the
>battery
>pack was backwards (alligator clips).
>
>

       With the PIC drawing this much current with reverse polarity (and I
wonder what voltage the batteries were pulled down to), it seems that
just a PTC thermistor in series with the power supply would be adequate
protection.  the PIC acts like a diode across the supply.  Reverse
voltage forward biases that diode and drives the PTC into high
resistance.
       Reminds me of an April Fools "idea for design" I saw years ago.  It was
how to compute squares using a Z80.  The design used only two pins.  It
used the Z80 as a diode and took advantage of the square relationship
between applied voltage and current.

Harold


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1999\06\01@015037 by Eric Smith

flavicon
face
> I wonder if the PIC will be damaged at all with a 3V reversed battery.
>
> Every protection diode on the IO pins will be conducting between VCC and
> GND rails in the chip, thus trying to drop the battery voltage to around
> 1.2V.
>
> Maybe no damaging current is available to flow into the chips' 'guts'.

OK, so you only blow the I/O pins.  That still renders the part unusable,
and the product failed.

And even if putting hundreds of milliamps through the I/O pads doesn't
kill them outright, it stresses them something fierce.  At this point there
is no way to count on the product operating reliably in the future.

1999\06\01@025015 by kfisk

flavicon
face
I've missed most of this discussion so maybe this has been suggested or
ruled out; However at over 6 Volts, couldn't you live with a Schottky diode
drop and just place this on the + side of the battery? In fact, you could
create a diode bridge which would still operate the system even when the
batteries where installed backwards. Mind you, the added cost may not be
tolerated.

Like I said, I joined this conversation late, so if I'm way off base then
please just delete me ;)

Cheers,

Kevin

{Quote hidden}

1999\06\01@041008 by Benjamin Petersen

flavicon
face
> -----Original Message-----
> From: pic microcontroller discussion list
> [TakeThisOuTPICLIST.....spamTakeThisOuTMITVMA.MIT.EDU]On Behalf Of Dennis Plunkett
> Sent: Tuesday, June 01, 1999 1:19 AM
> To: TakeThisOuTPICLISTKILLspamspamspamMITVMA.MIT.EDU
> Subject: Re: Reverse Polarity Protection for 3V PIC Circuit.
>
> > If they would
> >have been
> >paying attention, they wouldn't have put the batteries in
> backwards, and
> >they
> >would not have had the inconvienence of a blown fuse.  But
> they only lost a
> >fuse
> >and a little time, not the whole unit.
> >
>
> Fuses in battery operated devices (Hand held) since when?

Just think of a multimeter :-)

(I know that the fuse is for the external input, so don't even bother)

Regards
Benjamin Petersen

1999\06\01@084123 by wwl

picon face
On Mon, 31 May 1999 17:43:30 -0700, you wrote:

{Quote hidden}

I don't know where you buy fuses, but I think you're being ripped off!

1999\06\01@123240 by Sean Breheny

face picon face
Hmmmm, well, I suppose that WOULD work given the example I gave, but let me
change it a bit <G>

What about a device which draws 1 amp normally? You would at least need a
bigger bulb(to prevent it from lighting,resistance increasing,and dropping
significant voltage)! <G>

I do have to admit that I didn't think of the bulb.

Sean

At 02:03 PM 6/1/99 +1000, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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1999\06\01@183140 by wagnerl

picon face
There is a battery cell holder that does not allow a reversed cell to
make contact with the positive side. It has a kind of "plastic isolator"
that allows  only the positive button of the cell to make contact with
the positive connector.  It is somehow a plastic ring 1mm tickness.
When reversed, the cell positive button does contact the negative
contact (spring), while the negative side of the cell can not make
contact with the positive contact because the plastic ring.

Come on, after 50 years of battery usage, people is already expert in
install batteries with correct polarity... after realize it was wrong by
the first try... :)

After 50 years of battery usage and mistakes, I think it is time to
change the batteries package, with a center pin being the positive and a
ring as the negative, *on both extremes*..., then you don't need to care
about polarity anymore.   So we would have  AA-2, AAA-2, C-2, D-2 and so
on (2 = connection on both sides).

Wagner.

1999\06\01@185455 by paulb

flavicon
face
Sean Breheny wrote:

> Hmmmm, well, I suppose that WOULD work given the example I gave, but
> let me change it a bit <G>

> What about a device which draws 1 amp normally?  You would at least
> need a bigger bulb (to prevent it from lighting, resistance
> increasing, and dropping significant voltage)! <G>

 Firstly name me an appliance that draws one amp at 3V and may be
damaged by reverse polarity?  For 6V (may be tricky) and certainly 12V,
you use automotive lamps.

> I do have to admit that I didn't think of the bulb.

 It's terribly elegant isn't it?  In one fell swoop, it's extremely
cheap and readily available, has exactly the desired characteristic and
is rated to dissipate the heat.
--
 Cheers,
       Paul B.

1999\06\01@202105 by Tony Nixon

flavicon
picon face
This topic seems to be getting more off topic and more and more
academic, so I decided to put the problem to the test, and sacrifice one
of my pet 16F84's. This has been a work horse of mine for some time now
and with the abuse it's had over time, must be a good candidate for
failure with this type of test.

I got a 1 amp power supply and set it at 3V.

I connected MCLR to VCC via a 10K resistor.

Then I connected +3V to pin 5(Vdd), and GND to pin 14(Vss) via a 10R
resistor and a digital ammeter. VDrop on the ammeter was a few 10's of
mV.

I let the circuit 'run' like this for a couple of hours.

The resistor was quite hot and was dropping 1.7V due to the circuit
drawing 170mA. This resistor would be negligible in a low power
application.

The PIC's temperature rise on the other hand was barely noticable.

I took the PIC out and read and verified the data in it's ROM and
EEPROM. [OK]
I reprogrammed and verified the chip a couple of times. [OK]
I ran it in an amphometer circuit at 4MHz which uses all IO pins. [OK]

Now, I guess, from an engineering point of view this test does not mean
much, but from a real world point of view, I would say that a reverse 3V
does no harm to the PIC. I don't have access to electron microscope
analysis of the IO diodes, but I would bet they are not damaged.

I doubt that button cells could supply 170mA for any damaging length of
time, so perhaps this problem is purely an academic one. The other
problem may be if the rest of the circuit is more sensitive to a
reversed battery.

Perhaps someone listening from Microchip could specify a current rating
for the IO diodes so we all know.


--
Best regards

Tony

PicNPoke - Multimedia 16F84 Beginners PIC Tools.

http://www.picnpoke.com
Email RemoveMEpicnpokespamspamBeGonecdi.com.au

1999\06\01@220633 by Sean Breheny

face picon face
I know the original thread was about 3v, but I thought it had grown more
general than that. One example of what I am talking about would be an
amateur radio HT or mobile radio. These often power the final amp directly
from the batteries(or 12v supply),to get the most voltage so that they can
get the most power. A diode drop here could be significant AND it would be
awkward to have an automotive lamp inside the (relatively small) chassis.

BUT, you do have an elegant idea in using the bulb for most items.

Sean

At 08:45 AM 6/2/99 +1000, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
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1999\06\01@225703 by Donald Riedinger

picon face
Put a 1n914 in series with battery + to PIC Vdd and a 1uf tantalum from
PIC Vdd and diode cathode to ground.  PIC is protected from reverse
polarity plus noise and spikes on unfiltered side of diode.  Works great
with transistor driven inductive loads of 1 amp with below 3 volt supply
if you you don't source any curent from the PIC.  It's the negative
spikes from the PIC or transistors driven by the PIC sinking current
that cause the problem.  Especially as voltage drops and internal
resistance increases in the battery.  Isolate the PIC.

Don

1999\06\01@230133 by Peter Homann

picon face
Hi,

Maxim have a switching regulator  with an input range of .8V to 1.65V
(single cell). I may use this in the production version of the product. It
has a low battery indicator output which I require. Also it has reverse
polarity protection for up to 2 minutes. After 2 minutes, performance of the
component is reduced Whatever that means?) I think the part number is
MAX1642.

I originally asked this question and would like to thank all those who
replied.

Initially for the prototype I will not put any reverse polarity protection
as the PIC should cope (I hope) and that I'm the dumb user who is going to
put the batteries in incorrectly.

For the production unit I will probably use the MAXIM chip as I want the
longer battery life it will provide, plus a low battery indicator, plus
reverse polarity protection.

For those who are interested, the unit will draw about 2mA most of the time
when active, with an interval every 5seconds where the unit will draw about
14mA for a period of ~40mS. The unit will run about 2 hours a day. It will
be in sleep mode for the rest of the time.

Thanks again for everyone's input.

Peter.
---
Peter Homann    Email:  TakeThisOuTpeterhspamspamadacel.com.au
Adacel Technologies Ltd _/_/_/ _/_/_/ _/ Phone:   +61 3 9596 2991
250 Bay St, Brighton   _/  _/   _/   _/  Fax:     +61 3 9596 2960
Victoria  3186        _/_/_/   _/   _/   Home:    +61 3 9555 5603
AUSTRALIA            _/  _/   _/   _/_/_/Mobile:      0414-494578
------------------------------------------------------------------------


|  -----Original Message-----
 >
|  > Do any of the micropower switching regulators (ie 3.3V
|  from a single cell)
|  > include reversed-battery protection?  In theory, at least,
|  they all ready
|  > include the low-voltage mosfet technology...
|
|  Don't know the answer to that.
|

1999\06\01@232924 by Dennis Plunkett

flavicon
face
At 12:43 2/06/99 +1000, you wrote:
>Hi,
>
>Maxim have a switching regulator  with an input range of .8V to 1.65V
>(single cell). I may use this in the production version of the product. It
>has a low battery indicator output which I require. Also it has reverse
>polarity protection for up to 2 minutes. After 2 minutes, performance of the
>component is reduced Whatever that means?) I think the part number is
>MAX1642.
>
>I originally asked this question and would like to thank all those who
>replied.
>
>Initially for the prototype I will not put any reverse polarity protection
>as the PIC should cope (I hope) and that I'm the dumb user who is going to
>put the batteries in incorrectly.
>
>For the production unit I will probably use the MAXIM chip as I want the
>longer battery life it will provide, plus a low battery indicator, plus
>reverse polarity protection.

How will it provide longer battery life? The 0.8V flat level is deternimed
under load, from what I can see the advantage of this chip is single cell,
thus the size of the battery area can be reduced (If life expextencey is
OK) By the way is only 100days of operation OK?

Dennis

{Quote hidden}

1999\06\02@001903 by Peter Homann

picon face
See below

Thanks,


Peter.
---
Peter Homann    Email:  RemoveMEpeterhEraseMEspamspam_OUTadacel.com.au
Adacel Technologies Ltd _/_/_/ _/_/_/ _/ Phone:   +61 3 9596 2991
250 Bay St, Brighton   _/  _/   _/   _/  Fax:     +61 3 9596 2960
Victoria  3186        _/_/_/   _/   _/   Home:    +61 3 9555 5603
AUSTRALIA            _/  _/   _/   _/_/_/Mobile:      0414-494578
------------------------------------------------------------------------


|  -----Original Message-----

|  How will it provide longer battery life?

I plan to put the 2 N cells in parallel.

The 0.8V flat level
|  is deternimed
|  under load, from what I can see the advantage of this chip
|  is single cell,
|  thus the size of the battery area can be reduced (If life
|  expextencey is
|  OK) By the way is only 100days of operation OK?

Changing the batteries 3 to 4 times a year is acceptable.


|
|  Dennis
|


'Reverse Polarity Protection for 3V PIC Circuit.'
1999\07\20@172946 by Ansel Sermersheim
flavicon
face
>>>>> "Peter" == Peter Homann <@spam@peterhRemoveMEspamEraseMEADACEL.COM.AU> writes:

> Hi, Maxim have a switching regulator with an input range of .8V to
> 1.65V (single cell). I may use this in the production version of the
> product. It has a low battery indicator output which I require. Also
> it has reverse polarity protection for up to 2 minutes. After 2
> minutes, performance of the component is reduced Whatever that
> means?) I think the part number is MAX1642.

You might also want to look at the LT1110 from Linear.  Similar chip,
but specced at a maximum 750mA current with reversed battery, and rated
for continuous operation for reversed inputs less than 1.6V.

Digikey has them for $6.38 in onesies and $3.60 in hundreds.  I don't
see the MAX1642 there, so I don't know how that compares, but it might
be worth looking at.

-Ansel
--
It's all fun and games until someone loses an eye.     -Sergei
We can't quit.  If we quit now they'll kill us.        -Lab tech #2
       Pardon my writing; I'm using voice-recognition, and I
       sometimes don't catch all the errors.

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