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PICList Thread
'Polarity inversion protection'
1999\11\08@083729 by mazzoni michele

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Hello List,

I have realized an alarm for my bycicle using a 12C508. It is powered by two AA
size alkaline battery.

I would like to know if there is a simple (and economic!!) solution which
I can use to protect my circuit against polarity inversion during battery change
.
(I know it's a remote possibility, but it exists)

I thought to use a serie diode, but the voltage drop bring the PIC power voltage
near the power supply limit of the MCU.

Thanks.


Best regards,
Michele

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1999\11\08@085639 by Terry A. Steen

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How about putting a diode (or more) reversed bias parallel to the power
source. If the polarity IS reversed, you will only get a negative voltage
equal to the forward voltage drop of the diode. This will work as long at
the current doesn't kill the diode, so don't try using with a lead-acid
battery application!

If you know your supply current , you can use a current limit resistor. Use
R=(Vsource-Vdiode)/Imax diode. You can then double check to ensure the
supply voltage will not drop too much.

Good luck

       Current Limiting
(Vs)---------/\/\/\/---------------------> To device
                             |
                             _ Diode
                             ^ 1N4005
                             |
----------------------------------> Gnd


TAS
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1999\11\08@090227 by Jason Langenauer

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On Mon, 08 Nov 1999, you wrote:
> Hello List,
>
> I have realized an alarm for my bycicle using a 12C508. It is powered by two A
A
> size alkaline battery.
>
> I would like to know if there is a simple (and economic!!) solution which
> I can use to protect my circuit against polarity inversion during battery chan
ge.
> (I know it's a remote possibility, but it exists)
>
> I thought to use a serie diode, but the voltage drop bring the PIC power volta
ge
> near the power supply limit of the MCU.
>
I can't think of it right now, but there is an arrangement using a single
MOSFET which will provide this. Possibly the gate is connected to the drain,
possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz and
Hill. It's a very simple circuit, but as I said, I can't think of it now (such
is the effect of a few beers..). Play around with this, and see what you can
come up with. I'll try again in the morning.

Jason Langenauer
Mechanical and Space Enginnering, The University of Queensland
--
Lady Astor: If you were my husband, I'd poison you drink.
Winston Churchill : If I was your husband, I'd drink it.

1999\11\08@092939 by Terry A. Steen

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Yes, it is a diode connected mosfet.

TAS

At 10:03 AM 11/9/99 +1000, you wrote:
>On Mon, 08 Nov 1999, you wrote:
>> Hello List,
>>
>> I have realized an alarm for my bycicle using a 12C508. It is powered by
two AA
>> size alkaline battery.
>>
>> I would like to know if there is a simple (and economic!!) solution which
>> I can use to protect my circuit against polarity inversion during
battery change.
>> (I know it's a remote possibility, but it exists)
>>
>> I thought to use a serie diode, but the voltage drop bring the PIC power
voltage
>> near the power supply limit of the MCU.
>>
>I can't think of it right now, but there is an arrangement using a single
>MOSFET which will provide this. Possibly the gate is connected to the drain,
>possibly it is an N-channel MOSFET, and possibly the circuit is in
Horowitz and
>Hill. It's a very simple circuit, but as I said, I can't think of it now
(such
>is the effect of a few beers..). Play around with this, and see what you can
>come up with. I'll try again in the morning.
>
>Jason Langenauer
>Mechanical and Space Enginnering, The University of Queensland
>--
>Lady Astor: If you were my husband, I'd poison you drink.
>Winston Churchill : If I was your husband, I'd drink it.
>
>
-----------------------------------------------------------------
Sent from the desk of:
Terry Allen Steen, EE              .....engineeringKILLspamspam@spam@marinapower.com
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Williamsburg, Va   23185           757-258-8805 (FAX)
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1999\11\08@093200 by Wagner Lipnharski
picon face
Ok, use a reversed diode to the PIC with a low value resistor in series
to the cells. It means, that if reversing cells polarity it will be
drained by the resistor+diode. In real you would be short circuiting the
cells, but not in a dangerous current (limited by the resistor).
Calculate the resistor to drop only 50mV on normal operation, but when
cells are inverted it will dissipate heat, leaving only the diode
voltage drop to the PIC.

For example, if the normal operation current is around 10mA, the
resistor should be 50mV/10mA = 5 Ohms.  If cells are assembled reversed,
the diode will conduct directly over the resistor, so it will be
3V-0.6V(diode) / 5 Ohms = 480mA, enough to keep the reversed voltage
over the PIC at 0.6V without exploding the cells.

For better protection, you could use a Schottky diode or even an "old
germanium diode" that drops only 0.2Vdc.
If your circuit drain pulses of high current, bigger than 10mA, you can
add an electrolytic capacitor in parallel to the 5 Ohms diode, as a
bypass to those high surge periods.

For sure, if you can afford to reduce 0.2Vdc from the PIC, install only
the germanium diode in series with the cells... :)

Wagner.




Jason Langenauer wrote:
>
> On Mon, 08 Nov 1999, you wrote:
> > Hello List,
> >
> > I have realized an alarm for my bycicle using a 12C508. It is powered by two
AA
> > size alkaline battery.
> >
> > I would like to know if there is a simple (and economic!!) solution which
> > I can use to protect my circuit against polarity inversion during battery ch
ange.
> > (I know it's a remote possibility, but it exists)
> >
> > I thought to use a serie diode, but the voltage drop bring the PIC power vol
tage
{Quote hidden}

1999\11\08@094234 by David Covick

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face
Terry,

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 battery 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.
You may also require a 5 volt logic mosfet, which will turn on around 2
volts.

The diode approach is probably the best rather than the above if it is for
an inexpensive project.

David




<Hello List,
<
<I have realized an alarm for my bycicle using a 12C508. It is powered by
two AA
<size alkaline battery.
<
<I would like to know if there is a simple (and economic!!) solution which
<I can use to protect my circuit against polarity inversion during battery
change.
<(I know it's a remote possibility, but it exists)
<
<I thought to use a serie diode, but the voltage drop bring the PIC power
voltage
<near the power supply limit of the MCU.
<
Thanks.
<
<
<Best regards,
<Michele

1999\11\08@104548 by Harold Hallikainen

picon face
       How about a series PTC then a shunt diode.  The diode will conduct if
the batteries are put in backwards, opening the PTC.

Harold

On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele <mazzonispamKILLspamTECHEMAIL.COM>
writes:
{Quote hidden}

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1999\11\08@111553 by Nick Taylor

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Harold's suggestion is good, but it can be improved by using an
appropriate valued zener for the diode ... also gives overvoltage
protection.  It's saved my breadboard circuits from frying more
than once.
- Nick -

Harold Hallikainen wrote:
{Quote hidden}

1999\11\08@145508 by steve

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> I thought to use a serie diode, but the voltage drop bring the PIC power volta
ge
> near the power supply limit of the MCU.

I've  just been through this exercise for a similar circuit to
protect against the batteries being put in backwards.

Initially I used a Zetex ZVP4424A low Vgs, P-channel, enhancement
mode FET. Just tie the Gate to your negative terminal. When the
circuit is connected backwards, the FET is biased off and the
Drain/Source diode is reverse biased. When it is the right way
around, the diode is forward biased and gets shunted by the FET
turning on when the voltage starts to pass the Vgs threshold.

Eventually I changed this to just a schottky diode because all of the
loads could cope with reverse connection (eg. LEDs, dc motor switched
by transistor, etc) and I could put those on the battery side of the
diode. That just left the PIC drawing about 25uA which puts the
voltage drop well down on the curve so the diode is only costing
around < 0.15V. You have to look carefully at your circuit and
calculate what will happen at power up (reset time vs. circuit
capacitance).
The diode is cheaper but it comes with trade-offs. The FET is simple
and works well. It just costs a bit more (which wasn't acceptable for
my case).

One thing that caught me was that the 16C54 and 16C54A (LP) are
spec'd down to 2.5V but the later revisions (B & C) are only spec'd
(and operate)  down to 3V.This is the opposite to what I thought was
the effect of a die shrink (ie. specs stay the same or get better)
but the Microchip man at ESC had a plausable explanation so I'm
better educated now. Watch out for die shrunk parts.

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: EraseMEstevebspam_OUTspamTakeThisOuTtla.co.nz      fax +64 9 820-1929
======================================================

1999\11\08@191624 by Harold M Hallikainen

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       Yes, an even better idea!  I had not thought of that for this
application, but it sounds good.  In the products I've done, I don't know
how someone could stuff more AA cells in there than I had designed for,
but SOMEONE could overvoltage it!

Harold



Harold Hallikainen
haroldspamspam_OUThallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

On Mon, 8 Nov 1999 08:14:03 -0800 Nick Taylor <@spam@ntaylorKILLspamspamINAME.COM> writes:
{Quote hidden}

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1999\11\08@200856 by Mark Willis

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Easy;  Someone writes up a "How to run this off an AC to DC adapter, by
adding a power socket" web page, then someone who doesn't know what
they're doing sticks a 48VDC 300 mA power lump into that socket, blowing
things up if not protected.  (I've seen this done, sadly;  Also quite
often just "any handy power lump that fits" is assumed to work just
fine, a Zener is a GOOD idea, so's the FET.)

An idea on this:  How about a Unidirectional TVS (Transient Voltage
Suppressor) instead of a Zener?  They're fast, cheap, and have pretty
high peak power ratings;  I am not sure what their average power ratings
are, which is why I'll ask if anyone knows what average power rating a
600W TVS will handle - anyone?  I can just cook one to destruction, I
suppose <G>  (Also:  I need the spice models for these, both uni- and
bi-directionals;  if anyone has those handy, it'd be nice!  Off-list, of
course <G>)

 Mark  (about 1/2 here today.)

Harold M Hallikainen wrote:
{Quote hidden}

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1999\11\09@015542 by Dr. Imre Bartfai

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Hi,
I would use a serial connected Schottky.
Regards,
Imre


On Mon, 8 Nov 1999, Wagner Lipnharski wrote:

{Quote hidden}

wo AA
> > > size alkaline battery.
> > >
> > > I would like to know if there is a simple (and economic!!) solution which
> > > I can use to protect my circuit against polarity inversion during battery
change.
> > > (I know it's a remote possibility, but it exists)
> > >
> > > I thought to use a serie diode, but the voltage drop bring the PIC power v
oltage
> > > near the power supply limit of the MCU.
> > >
> > I can't think of it right now, but there is an arrangement using a single
> > MOSFET which will provide this. Possibly the gate is connected to the drain,
> > possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz
and
> > Hill. It's a very simple circuit, but as I said, I can't think of it now (su
ch
{Quote hidden}

1999\11\09@212921 by Hekan Barregerd

picon face
<x-flowed>If the battery holder is of the tube type with a spring in the bottom and a
flat piece of metal on the top then you can cut a circle the size of the
battery from a piece of tape. Make a hole so the + pole on the battery can
make contact. Then stick it on the + connector of the battery holder.

Best regards,
Hekan

{Quote hidden}

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</x-flowed>

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