Favorite reverse bias protection for battery circuits [Design]

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From: Jim Thompson on 17 Mar 2010 16:37

On Wed, 17 Mar 2010 10:51:53 -0700, Charlie E. <edmondson(a)ieee.org>
wrote:

>On Wed, 17 Mar 2010 10:26:37 -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
>>
>>WHAT is an MC1253? Maybe local protection?
>>
>> ...Jim Thompson
>
>It's a Microchip charge pump regulator. Using two, one to provide
>3.3VDC for most of the circuit, and one to boost the LED drive to a
>constant current of 20mA. Although, I am thinking of lowering that to
>12mA to give more life...
>
>Charlie

Googling on MC1253 yields nada... You typo'd... it's MCP1253 :-)

Just put an NPN in the ground feed.

...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: legg on 18 Mar 2010 07:18

>On Tue, 16 Mar 2010 17:57:01 -0500, Vladimir Vassilevsky <nospam(a)nowhere.com> wrote:

>Charlie E. wrote:
<snip>
>
>
>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

Cowards: No V/I characteristics around zero.

Hides a potential can of worms.

...... the normally-off synchronous rectifier has been a bee in my
bonnet for a long time.

RL

From: dagmargoodboat on 18 Mar 2010 09:08

On Mar 16, 1:18 pm, Joerg <inva...(a)invalid.invalid> wrote:
> Hammy wrote:
> > On Tue, 16 Mar 2010 10:56:46 -0700, 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.
>
> >> Thanks!
>
> >> Charlie
> > I usually use #2 on this page a shorting shottky.
>
> >http://www.recom-international.com/press/Reverse%20Polarity%20Protect...
>
> 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

Joerg, you big spender! Use an n-FET--they're better and cheaper--in
the ground lead.

--
Cheers,
James Arthur

From: Joerg on 18 Mar 2010 13:25

dagmargoodboat(a)yahoo.com wrote:
> On Mar 16, 1:18 pm, Joerg <inva...(a)invalid.invalid> wrote:
>> Hammy wrote:
>>> On Tue, 16 Mar 2010 10:56:46 -0700, 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.
>>>> Thanks!
>>>> Charlie
>>> I usually use #2 on this page a shorting shottky.
>>> http://www.recom-international.com/press/Reverse%20Polarity%20Protect...
>> 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
>
> Joerg, you big spender! Use an n-FET--they're better and cheaper--in
> the ground lead.
>

Yup, that's what I'd do in this case :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

From: Jim Thompson on 18 Mar 2010 13:53

On Thu, 18 Mar 2010 10:25:17 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>dagmargoodboat(a)yahoo.com wrote:
>> On Mar 16, 1:18 pm, Joerg <inva...(a)invalid.invalid> wrote:
>>> Hammy wrote:
>>>> On Tue, 16 Mar 2010 10:56:46 -0700, 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.
>>>>> Thanks!
>>>>> Charlie
>>>> I usually use #2 on this page a shorting shottky.
>>>> http://www.recom-international.com/press/Reverse%20Polarity%20Protect...
>>> 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
>>
>> Joerg, you big spender! Use an n-FET--they're better and cheaper--in
>> the ground lead.
>>
>
>Yup, that's what I'd do in this case :-)

Where do you get a discrete NMOSFET that will be thoroughly on at 1.8V
VGS?

The Micrel part _may_ work.

...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