Favorite reverse bias protection for battery circuits [Design]

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From: Jim Thompson on 16 Mar 2010 18:35

On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org>
wrote:

>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

See...

Newsgroups: alt.binaries.schematics.electronic
Subject: Battery Reversal Protection (from SED) -
BatteryReversalProtection.pdf
Date: Tue, 16 Mar 2010 15:32:36 -0700
Message-ID: <6l10q59eb80bgcp4gfklr9bq18qsbrtrtk(a)4ax.com>

But pick a better transistor, with lower saturation. I don't store
discrete transistor data in my head like I do ASIC processes :-)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The only thing bipartisan in this country is hypocrisy

From: Martin Riddle on 16 Mar 2010 18:40

"Joerg" <invalid(a)invalid.invalid> wrote in message
news:80a0b7F5q1U2(a)mid.individual.net...
> Hammy wrote:
>> On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org>
>> wrote:
>>
>>> 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%20Polarity%20Protection%20for%20DC/DC%20Converters.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.
>
> --
> Regards, Joerg
>

You can replace the fuse with a PTC, batteries might not like it, but it
would still function when the batteries are inserted correctly.

Cheers

From: D Yuniskis on 16 Mar 2010 19:03

Joerg wrote:
> D Yuniskis wrote:
>> Hi Joerg,
>>
>> Joerg wrote:
>>> D Yuniskis wrote:
>>>>>> "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...
>>>>
>>>> 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.
>>
>> 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.
>
> Very tough. I had tried that at times in the past and there ain't much
> out there. Even the ready-to-go enclosures with built-in compartment
> that I came across aren't really good in that respect.

I've been eying the Bulgin products. MPD and Keystone
tend to be bottom feeder designs which haven't impressed
me. But, I'm currently designing for much higher power
requirements so batteries (at least standard cells)
aren't an option.

>> 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)
>
> I have one, in case of a trip way into the boonies (those are Li
> batteries so they'll last longer). Very expensive, not really an option
> for everyday use.

Are you sure? The ones I have are made by Duracell (though
none of them are in convenient places for me to examine).
I would imagine a "colorimeter" sees infrequent use so
you would want a battery that's going to be "there for you"...
(My pet peeve re: flashlights is you use them so infrequently
that the batteries are *always* dead when you need them)

>>>>> 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)
>>>
>>> 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.
>
> Yes, that's usually good enough. No audio feedback -> something must be
> wrong with the batteries.

*If* the audio feedback in normal operation is noticeable
enough. E.g., audio annunciators in most *cars* are
ineffective as: 1) there are too many of them 2) they
don't "complain" enough.

I.e., make the "chirp" something distinctive (a little
tune) so it's noticeable without being obnoxious -- and
"missed" when absent.

E.g., you could power up a Windows PC with your eyes closed
and would "notice" if their silly little tune didn't play...

From: Jim Thompson on 16 Mar 2010 18:53

On Tue, 16 Mar 2010 15:35:57 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote:

>On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org>
>wrote:
>
>>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
>
>See...
>
>Newsgroups: alt.binaries.schematics.electronic
>Subject: Battery Reversal Protection (from SED) -
>BatteryReversalProtection.pdf
>Date: Tue, 16 Mar 2010 15:32:36 -0700
>Message-ID: <6l10q59eb80bgcp4gfklr9bq18qsbrtrtk(a)4ax.com>
>
>But pick a better transistor, with lower saturation. I don't store
>discrete transistor data in my head like I do ASIC processes :-)
>
> ...Jim Thompson

Of course, if you can get that proverbial PMOS with VT=0.7V, as I can
in ASIC's, you'd do this...

Newsgroups: alt.binaries.schematics.electronic
Subject: Re: Battery Reversal Protection (from SED) -
BatteryReversalProtection.pdf - BatteryReversalProtection-2.pdf
Date: Tue, 16 Mar 2010 15:51:15 -0700
Message-ID: <om20q55rp2gcfo182497qclispunbe61or(a)4ax.com>

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The only thing bipartisan in this country is hypocrisy

From: Vladimir Vassilevsky on 16 Mar 2010 18:57

Charlie E. wrote:

> 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.

I like LTC4358.

They took care of a lot of problems typical for trivial DIY reverse
battery protection circuits.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com