Favorite reverse bias protection for battery circuits [Design]

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From: Spehro Pefhany on 18 Mar 2010 14:11

On Thu, 18 Mar 2010 10:53:31 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote:

>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?

Here's one:
http://www.fairchildsemi.com/ds/FD%2FFDMA410NZ.pdf

50m ohm at 1.5V Vgs.

Does n-channel still offer a cost advantage over p-channel for very
low voltage devices?

Here's a p-channel device with 113m ohm at 1.2V Vgs.
http://www.vishay.com/docs/74620/sia419dj.pdf

Apparently a SC-70 can dissipate 19W if you can hold the case to
25�C...

>The Micrel part _may_ work.
>
> ...Jim Thompson

From: Joerg on 18 Mar 2010 14:57

Jim Thompson wrote:
> 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.
>

Plenty of others. If it has to be cheap (and somehow it always has to
be...), here's an example at around 15 cents, Rdson guaranteed down to 1.5V:

http://www.diodes.com/datasheets/ds31186.pdf

You need to get out into the world of discretes some more :-)

--
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 15:00

On Thu, 18 Mar 2010 14:11:36 -0400, Spehro Pefhany
<speffSNIP(a)interlogDOTyou.knowwhat> wrote:

>On Thu, 18 Mar 2010 10:53:31 -0700, Jim Thompson
><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote:
>
>>On Thu, 18 Mar 2010 10:25:17 -0700, Joerg <invalid(a)invalid.invalid>
>>wrote:
>>
>>>dagmargoodboat(a)yahoo.com wrote:
[snip]
>>>>>
>>>>> 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?
>
>Here's one:
>http://www.fairchildsemi.com/ds/FD%2FFDMA410NZ.pdf
>
>50m ohm at 1.5V Vgs.
>
>Does n-channel still offer a cost advantage over p-channel for very
>low voltage devices?

I don't think so...

>
>Here's a p-channel device with 113m ohm at 1.2V Vgs.
>http://www.vishay.com/docs/74620/sia419dj.pdf

It appears that the N-channel part is made on an P-substrate and
vice-versa.

>
>Apparently a SC-70 can dissipate 19W if you can hold the case to
>25�C...
>
[snip]

Nice devices!

...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: Jim Thompson on 18 Mar 2010 15:07

On Thu, 18 Mar 2010 11:57:26 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>Jim Thompson wrote:
>> 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:
[snip]
>>>>>
>>>>> 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.
>>
>
>Plenty of others. If it has to be cheap (and somehow it always has to
>be...), here's an example at around 15 cents, Rdson guaranteed down to 1.5V:
>
>http://www.diodes.com/datasheets/ds31186.pdf
>
>You need to get out into the world of discretes some more :-)

Nope! I avoid markets that are priced like popcorn.

Except for my own G-jobs :-)

...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: Joerg on 18 Mar 2010 15:26

Jim Thompson wrote:
> On Thu, 18 Mar 2010 11:57:26 -0700, Joerg <invalid(a)invalid.invalid>
> wrote:
>
>> Jim Thompson wrote:
>>> 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:
> [snip]
>>>>>> 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.
>>>
>> Plenty of others. If it has to be cheap (and somehow it always has to
>> be...), here's an example at around 15 cents, Rdson guaranteed down to 1.5V:
>>
>> http://www.diodes.com/datasheets/ds31186.pdf
>>
>> You need to get out into the world of discretes some more :-)
>
> Nope! I avoid markets that are priced like popcorn.
>

Oh, it's not always that way. Roughly half of my designs aren't required
to be rock-bottom in BOM cost. Although I can't help it, the calculator
in my head is always running. Sometimes clients are surprised when they
see the (working) circuit. "You mean, that's it?"

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

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