Favorite reverse bias protection for battery circuits

[Charlie E.]

Hi All,
Still working on my color reader, and getting close. Biggest problem
is that now I have almost TOO much drive on my LEDs, but that I can
deal with!

Now, to the latest problem. My system is for the visually impaired. I
just put the batteries in one of my prototypes backwards, and it
didn't last very long. While I expect this device to have very long
battery life, since it normally doesn't operate but for a second or
two, it looks like the MC1253's don't like getting reversed biased
very long. So, for my design question of the day - What is your
favorite circuit for preventing reverse bias from the batteries? The
old diode trick drops too much voltage, so wondered if there are any
clever FET tricks to block backwards voltages.

Thanks!

Charlie

 

[BillyGates]

Hi All,
Still working on my color reader, and getting close. Biggest problem
is that now I have almost TOO much drive on my LEDs, but that I can
deal with!

Now, to the latest problem. My system is for the visually impaired. I
just put the batteries in one of my prototypes backwards, and it
didn't last very long. While I expect this device to have very long
battery life, since it normally doesn't operate but for a second or
two, it looks like the MC1253's don't like getting reversed biased
very long. So, for my design question of the day - What is your
favorite circuit for preventing reverse bias from the batteries? The
old diode trick drops too much voltage, so wondered if there are any
clever FET tricks to block backwards voltages.

Thanks!

Charlie

Yes, there are fet "tricks" that when reverse biased bias the fet to turn it
off. It is essentially an "active diode".

 

[Hammy]

Hi All,
Still working on my color reader, and getting close. Biggest problem
is that now I have almost TOO much drive on my LEDs, but that I can
deal with!

Now, to the latest problem. My system is for the visually impaired. I
just put the batteries in one of my prototypes backwards, and it
didn't last very long. While I expect this device to have very long
battery life, since it normally doesn't operate but for a second or
two, it looks like the MC1253's don't like getting reversed biased
very long. So, for my design question of the day - What is your
favorite circuit for preventing reverse bias from the batteries? The
old diode trick drops too much voltage, so wondered if there are any
clever FET tricks to block backwards voltages.

Thanks!

Charlie

I usually use #2 on this page a shorting shottky.

http://www.recom-international.com/press/Reverse Polarity Protection for DC/DC Converters.html

 

[Rich Webb]

Hi All,
Still working on my color reader, and getting close. Biggest problem
is that now I have almost TOO much drive on my LEDs, but that I can
deal with!

Now, to the latest problem. My system is for the visually impaired. I
just put the batteries in one of my prototypes backwards, and it
didn't last very long. While I expect this device to have very long
battery life, since it normally doesn't operate but for a second or
two, it looks like the MC1253's don't like getting reversed biased
very long. So, for my design question of the day - What is your
favorite circuit for preventing reverse bias from the batteries? The
old diode trick drops too much voltage, so wondered if there are any
clever FET tricks to block backwards voltages.

This http://www.maxim-ic.com/app-notes/index.mvp/id/636 Maxim appnote
describes the pros and cons of several standard approaches.

 

[Joerg]

I usually use #2 on this page a shorting shottky.

http://www.recom-international.com/press/Reverse Polarity Protection for DC/DC Converters.html

That renders the unit dead and a blind or almost blind person will have
a hard time finding or buying the proper fuse and installing it.

Charlie: Solution #3 is the ticket (look on Hammy's link). But make sure
that the FET is guaranteed to be fully turned on at the lowest allowed
battery voltage, IOW the point where an UVLO comes on.

 

[Joerg]

Some variation on this...

http://analog-innovations.com/SED/PerfectDiodeForChargerIsolation.pdf

Do you have enough voltage to turn on MOSFET's?

Probably could do it with bipolar's... I'll ponder

Which HV CMOS process did that get rolled onto, if I may ask?

 

[D Yuniskis]

Hi Charlie,

Still working on my color reader, and getting close. Biggest problem
is that now I have almost TOO much drive on my LEDs, but that I can
deal with!

Now, to the latest problem. My system is for the visually impaired. I
just put the batteries in one of my prototypes backwards, and it
didn't last very long. While I expect this device to have very long
battery life, since it normally doesn't operate but for a second or
two, it looks like the MC1253's don't like getting reversed biased
very long. So, for my design question of the day - What is your
favorite circuit for preventing reverse bias from the batteries? The
old diode trick drops too much voltage, so wondered if there are any
clever FET tricks to block backwards voltages.

Solve this problem *mechanically*. You need to prevent the
batteries from being *installed* wrong, in the first place.
E.g., any sort of circuit that protects (the rest of) the
circuit from reversed battery won't do anything to tell the
VI user *why* your device isn't working. Are the batteries
*dead*? Installed wrong? Corroded terminals? Or is the
*device* broken??

"Key" the battery holder so the user can feel the correct
orientation for the batteries *and* so it prevents the
cells from making electrical contact if not oriented
properly.

Think of how the *user* is going to interact with your device.
Close your eyes and "figure out" why it doesn't work :-/

 

[Hammy]

That renders the unit dead and a blind or almost blind person will have
a hard time finding or buying the proper fuse and installing it.

Thats what they have seeing eye dogs for Jokeing.

Of course your right for a blind person either #3 or a keyed battery
connection. With a brail instruction manual

 

[Joerg]

California Micro Devices (do they still exist?) for a LiIon
charge/discharge controller.

Swallowed by ON, just like AMI was :-(

 

[Joerg]

Thats what they have seeing eye dogs for Jokeing.

Ok, I'll ask our new Labrador when she is back

She went through the first three phases of guide dog training and then
had to be discharged for a medical condition (soft trachea, happens a
lot with guide dog Labs).

Of course your right for a blind person either #3 or a keyed battery
connection. With a brail instruction manual

It's actually even better these days. A nearly blind relative has a
Casio watch that talks.

 

[Charlie E.]

Hi Charlie,


Solve this problem *mechanically*. You need to prevent the
batteries from being *installed* wrong, in the first place.
E.g., any sort of circuit that protects (the rest of) the
circuit from reversed battery won't do anything to tell the
VI user *why* your device isn't working. Are the batteries
*dead*? Installed wrong? Corroded terminals? Or is the
*device* broken??

"Key" the battery holder so the user can feel the correct
orientation for the batteries *and* so it prevents the
cells from making electrical contact if not oriented
properly.

Think of how the *user* is going to interact with your device.
Close your eyes and "figure out" why it doesn't work :-/

Would be the best result, but these are standard AA cells, no way to
key them without using expensive custom battery packs. Not the way to
go for inexpensive...

Will be looking for a good PMOS FET that will still conduct with two
low AA batteries, probably around 1.8VDC, if they make one! ;-)

Thanks All!

Charlie

 

[D Yuniskis]

Hi Charlie,

Would be the best result, but these are standard AA cells, no way to
key them without using expensive custom battery packs. Not the way to
go for inexpensive...

I take it you aren't making a custom (molded) case?
Why not purchase COTS battery holder that *is* "keyed"?

Will be looking for a good PMOS FET that will still conduct with two
low AA batteries, probably around 1.8VDC, if they make one! ;-)

If you go that route, consider how your design can tell the user
"yes, I am working" vs. absence of that indication so the user
can deduce "something is wrong with the batteries or their
installation" (or the device)

 

[Hammy]

Ok, I'll ask our new Labrador when she is back

She went through the first three phases of guide dog training and then
had to be discharged for a medical condition (soft trachea, happens a
lot with guide dog Labs).

Are you a foster dad for pups?
You must dread having to give them up?

I just took my Golden Retriever to the vet. He started to develop a
sunken eye. The vet doesn't know the cause yet. I'm hoping its nothing
to serious.

It's actually even better these days. A nearly blind relative has a
Casio watch that talks.

That's nothing look at Hawkins chair that dude is wired for sound and
then some.

 

[Joerg]

Are you a foster dad for pups?
You must dread having to give them up?

No, we are puppy sitters. So we jump in when a family goes on vacation
or visits a sick relative where they can't take the guide dog puppy.
Even then it's tough when they have to go back to San Rafael, especially
for my wife since she sees them every week during trainings. But when
you see them paired up with a blind person you know it's all worth it.

We used to also sit the one that came home now. She instantly remembered
our other dogs, where everything is in the house, etc.

I just took my Golden Retriever to the vet. He started to develop a
sunken eye. The vet doesn't know the cause yet. I'm hoping its nothing
to serious.

Hopefully not. Our Rottweiler is now at an age where it's just a matter
of time :-(

That's nothing look at Hawkins chair that dude is wired for sound and
then some.

No idea what a Hawkins chair is.

<scratching_head>

[...]

 

[Charlie E.]

Are you a foster dad for pups?
You must dread having to give them up?

No, we are puppy sitters. So we jump in when a family goes on vacation
or visits a sick relative where they can't take the guide dog puppy.
Even then it's tough when they have to go back to San Rafael, especially
for my wife since she sees them every week during trainings. But when
you see them paired up with a blind person you know it's all worth it.

We used to also sit the one that came home now. She instantly remembered
our other dogs, where everything is in the house, etc.

I just took my Golden Retriever to the vet. He started to develop a
sunken eye. The vet doesn't know the cause yet. I'm hoping its nothing
to serious.

Hopefully not. Our Rottweiler is now at an age where it's just a matter
of time :-(

That's nothing look at Hawkins chair that dude is wired for sound and
then some.

No idea what a Hawkins chair is.

<scratching_head>

[...]

He's talking Stephen Hawkins (sp?) the physicist with MS.

Well, my wife's computer talks to her, she has two watches that talk
(one red, one blue) a talking calculator that includes a calendar and
timer function, and another talking calculator that just does math...

Charlie

 

[Hammy]

Hopefully not. Our Rottweiler is now at an age where it's just a matter
of time :-(

Mine just turned 9. My last one was 11 when he died.

That's nothing look at Hawkins chair that dude is wired for sound and
then some.

No idea what a Hawkins chair is.

<scratching_head>

[...]

He's that British theoretical physicist who came up with a theory for
the origin of the universe among other things.

http://en.wikipedia.org/wiki/Stephen_Hawking

He has amyotrophic lateral sclerosis. So he uses a chair with all
sorts of gadgets on it.

 

[Joerg]

That renders the unit dead and a blind or almost blind person will have
a hard time finding or buying the proper fuse and installing it.
Thats what they have seeing eye dogs for Jokeing.

Ok, I'll ask our new Labrador when she is back

She went through the first three phases of guide dog training and then
had to be discharged for a medical condition (soft trachea, happens a
lot with guide dog Labs).
Are you a foster dad for pups?
You must dread having to give them up?

No, we are puppy sitters. So we jump in when a family goes on vacation
or visits a sick relative where they can't take the guide dog puppy.
Even then it's tough when they have to go back to San Rafael, especially
for my wife since she sees them every week during trainings. But when
you see them paired up with a blind person you know it's all worth it.

We used to also sit the one that came home now. She instantly remembered
our other dogs, where everything is in the house, etc.

I just took my Golden Retriever to the vet. He started to develop a
sunken eye. The vet doesn't know the cause yet. I'm hoping its nothing
to serious.

Hopefully not. Our Rottweiler is now at an age where it's just a matter
of time :-(

Of course your right for a blind person either #3 or a keyed battery
connection. With a brail instruction manual

It's actually even better these days. A nearly blind relative has a
Casio watch that talks.
That's nothing look at Hawkins chair that dude is wired for sound and
then some.

No idea what a Hawkins chair is.

<scratching_head>

[...]

He's talking Stephen Hawkins (sp?) the physicist with MS.

Ah yes, Stephen Hawking:

http://en.wikipedia.org/wiki/Stephen_Hawking

Well, my wife's computer talks to her, she has two watches that talk
(one red, one blue) a talking calculator that includes a calendar and
timer function, and another talking calculator that just does math...

Once a disabled person masters technology it can add so much to their
abilities.

Same with non-tech skills. A neighbor is deaf and he and his brothers
can "talk" from vehicle to vehicle without any technology, by signing.
It's amazing. But he also uses video phones etc.

 

[Joerg]

Hi Charlie,


I take it you aren't making a custom (molded) case?
Why not purchase COTS battery holder that *is* "keyed"?

Anything other than AA cells is expensive. And as Charlie wrote AA cells
are difficult to key without going to precision molding or milling.

If you go that route, consider how your design can tell the user
"yes, I am working" vs. absence of that indication so the user
can deduce "something is wrong with the batteries or their
installation" (or the device)

Very easy: Oscillator that is connected via a diode so it works only
when batteries are reversed, drives piezo. Battery inserted the wrong
way -> beep ... beep ... beep ...

If you want to also cover the case where only one of the batteries is
reversed use two of those, can drive the same piezo.

 

[Joerg]

Called a PNP

What's the load current?

Why PMOS?

 

[D Yuniskis]

Hi Joerg,

Anything other than AA cells is expensive. And as Charlie wrote AA cells
are difficult to key without going to precision molding or milling.

Yes. Find a battery holder that someone *else* has incurred
the cost of that molding! Preferably, something that lets
the user access the "battery compartment" without having
to disassemble the device itself.

OTOH, if he is making "one off", a bit of plastic glued on either
side of the '+' holder terminal can do the trick.

I'd also look for those (camera?) batteries (two cells side
by side... 3V?) as I think that is keyed (at the very
least, it eliminates the problem of putting one cell in
correct and one backwards)

Very easy: Oscillator that is connected via a diode so it works only
when batteries are reversed, drives piezo. Battery inserted the wrong
way -> beep ... beep ... beep ...

If you want to also cover the case where only one of the batteries is
reversed use two of those, can drive the same piezo.

You don't need to be that extravagant. Just something in the
*normal* usage of the device that people can count on for
feedback/confirmation. E.g., if the device uses audio
output (synthetic speech or just "tones"), then design
the device so that immediately on turning on, it "chirps"
once.

[I don't recall what he has chosen for his output medium;
personally, I would opt for limited vocabulary speech as
it can be *very* small]

This gives a positive indication to the user in *normal*
operation (i.e., those times when you HAVEN'T just
changed batteries) that the device is, in fact, "on".
And, knowing to expect this, it can be used when replacing
batteries to act as a confirmation that the batteries
are, in fact, installed correctly, aren't "dead", etc.