Favorite reverse bias protection for battery circuits [Design]

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From: Don Lancaster on 17 Mar 2010 00:05

krw(a)att.bizzzzzzzzzzzz 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.

Synchronous rectifier.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: don(a)tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com

From: Jan Panteltje on 17 Mar 2010 07:55

On a sunny day (Tue, 16 Mar 2010 17:13:43 -0700) it happened D Yuniskis
<not.going.to.be(a)seen.com> wrote in <hnp642$l9s$1(a)speranza.aioe.org>:

>Hi Jan,
>
>Jan Panteltje wrote:
>> Use a bigger batteriy and a bridge rectifier,
>> then it does not matter how they are put in.
>
>The device ends up larger. And weighs more, etc.
>
>For *one* device, this is no big deal. But, folks with
>disabilities tend to have *lots* of "special devices".
>Each is typically larger than it's counterpart (for
>the mainstream population).

I was joking!
But on a more serious note:
Most visually impaired have great sense in their fingers,
they will have no problem feeling what side of an AA of AAA goes where.

I can do it too wit heyes closed :-)

From: MooseFET on 17 Mar 2010 09:49

On Mar 16, 7:13 pm, Grant <o...(a)grrr.id.au> wrote:
> On Tue, 16 Mar 2010 18:43:58 -0700 (PDT), MooseFET <kensm...(a)rahul.net> wrote:
> >On Mar 16, 10:56 am, Charlie E. <edmond...(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.
>
> >I did a quick check and nobody mentioned the idea of a diode in
> >series
> >with a relay coil.
>
> That's because a relay coil likely draws more power than the circuit you're
> trying to protect ;)

I tend to be designing things that are called "portable" and run from
a car
battery or the like. Right now I am doing the lowest powered product
ever
and that is 2.5W.

>
> I like diode and polyswitch, or MOSFET circuit.

I have found that polyswitches can't be trusted if you have a
significant
battery to get hooked up backwards. They take too long to go open.

I have used the MOSFET trick

I used a diode to supply power to a little circuit that pumps the gate
of the MOSFET up so that the battery voltage doesn't have to be
enough
to work the MOSFET.

>
> Grant.

From: E on 17 Mar 2010 09:53

"Grant" <omg(a)grrr.id.au> kirjoitti
viestiss�:bhe0q5hnkemc8aluv1p1bg8krfurfnc133(a)4ax.com...
> On Tue, 16 Mar 2010 18:43:58 -0700 (PDT), MooseFET <kensmith(a)rahul.net>
> wrote:
>
>>On Mar 16, 10:56 am, Charlie E. <edmond...(a)ieee.org> wrote:

>>
>>I did a quick check and nobody mentioned the idea of a diode in
>>series
>>with a relay coil.
>
> That's because a relay coil likely draws more power than the circuit
> you're
> trying to protect ;)
>

But you can solve that power problem with impulse relay. Connect coil thru
diode so that it gets power when polarity is wrong and another flyback diode
across coil to ensure it goes all way to another position. Then when
polarity is
wrong relay gets power and changes polarity.

Only problem is that you have to find someone how makes such relays...

schematic:
http://koti.mbnet.fi/erkkak/imp/imp.png

-ek

From: John Fields on 17 Mar 2010 10:42

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.

---
View in courier:

If it's only on for a short time why not use a relay?

_____
+-----------------------O | O--+
| NO | |
+--O---> | | [LOAD]
|+ | | |
[BAT] O---[DIODE>]--[COIL]--+
| |
+------------------------------+

JF