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'[EE] Diode Protection'
2010\12\13@065634 by Jason White

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part 1 453 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

Hello, recently I have lost several ICs to reverse voltage and
occasionally to overvoltage. I'm asking what would be the best
configuration of diodes and caps to provide steady operation,
overvoltage and reverse voltage protection to an IC ? I've attached
what I think the circuit would look like, however I could be
completely wrong ...

Thanks


-- Jason White - C++ Programmer and Electronics Hobbyist


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part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
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2010\12\13@071023 by Sarin Sukumar A

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part 1 1299 bytes content-type:text/plain; charset="utf-8" (decoded base64)

Thats wrong. Circuit as in attached will work, You may add more filter and
decap capacitors if needed more regulation at the power supply

*Sarin Sukumar A*

*Design Engineer*

*ni Logic Pvt Ltd, Pune*

*☎** +91 9372195481*
My profiles: [image:
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Contact me: [image: Google Talk/] sarinsukumar [image: Skype/] sarinsukumar




On Mon, Dec 13, 2010 at 3:56 AM, Jason White <
spam_OUTwhitewaterssoftwareinfoTakeThisOuTspamgmail.com> wrote:

> Hello, recently I have lost several ICs to reverse voltage and
> occasionally to overvoltage. I'm asking what would be the best
> configuration of diodes and caps to provide steady operation,
> overvoltage and reverse voltage protection to an IC ? I've attached
> what I think the circuit would look like, however I could be
> completely wrong ...
>
> Thanks
>
>
> --
> Jason White - C++ Programmer and Electronics Hobbyist
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> mailman.mit.edu/mailman/listinfo/piclist
>
>

part 2 21065 bytes content-type:image/png; name="mail.png" (decode)


part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
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2010\12\13@072327 by Wouter van Ooijen

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On 13/12/2010 12:56 PM, Jason White wrote:
> Hello, recently I have lost several ICs to reverse voltage and
> occasionally to overvoltage. I'm asking what would be the best
> configuration of diodes and caps to provide steady operation,
> overvoltage and reverse voltage protection to an IC ? I've attached
> what I think the circuit would look like, however I could be
> completely wrong ...

I think
- 5.1V for the zener could be too low, an 7805 for instance has a rather wide tolerance
- the series diode is not needed, the zener is a normal diode too, so it would short a reverse power
- I think I would add a series fuse or polyfuse
- I would include some visual power indication, so you can see when you are applying the power wrong

I always include a reverse diode (aka "fools diode"). My way to prevent overvoltage is to stick to 5V parts, and use only 5V as 'accessible voltage' on my bench. Higher voltages (like 9-12V wall-warts) always terminate in a barrel plug.



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Wouter van Ooijen

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2010\12\13@072834 by Isaac Marino Bavaresco

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Em 13/12/2010 09:56, Jason White escreveu:
> Hello, recently I have lost several ICs to reverse voltage and
> occasionally to overvoltage. I'm asking what would be the best
> configuration of diodes and caps to provide steady operation,
> overvoltage and reverse voltage protection to an IC ? I've attached
> what I think the circuit would look like, however I could be
> completely wrong ...
>
> Thanks

Some notes/suggestions:

1) You swapped the names of Vss and Vdd outside of the chip.
2) It would be better if you use a ground symbol for Vss, pointing
downwards.
3) Your diode D0 is pointing in the wrong direction (swap anode and
cathode).
4) You should add a series resistor between the cathode of Z0 and the
power source.
5) Don't use Zn for zeners, they are diodes. Use Dn.
5) Don't use decimal points in the values of components. Use 5V1 instead
of 5.1V.
6) It would be better if your Zener diode were 5.6V (5V6).


Best regards,

Isaac

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2010\12\13@073412 by RussellMc

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Reverse D0.
Top right is designed to be Vdd.

D0 = Schottky usually better and OK.

Reverse connected MOSFET allows reverse battery protection at almost
no voltage drop.
eg NChannel.
Drain to gnd,
Source to IC -ve.
Gate to Vdd IC.
FET conducts if psu connected correctly.
Slightly more to cct than may at first appear.


       R




On 14 December 2010 00:56, Jason White
<.....whitewaterssoftwareinfoKILLspamspam@spam@gmail.com> wrote:
{Quote hidden}

>

2010\12\13@073542 by Olin Lathrop

face picon face
Jason White wrote:
> Hello, recently I have lost several ICs to reverse voltage and
> occasionally to overvoltage.

Before you even start trying to deal with the problem after the fault at the
PIC, find out how these conditions happened in the first place.  Why did the
voltage get too high?  What failed in the power supply to cause that?  How
can it possibly be connected backwards!?  Maybe you need keyed connectors?

> I'm asking what would be the best
> configuration of diodes and caps to provide steady operation,
> overvoltage and reverse voltage protection to an IC ? I've attached
> what I think the circuit would look like, however I could be
> completely wrong ...

1 - The zener (Z0) is backwards.

2 - There is no impedence shown for the zener to work against.  It won't
take much of a power supply to blow out the zener if the voltage got too
high somehow.

3 - The regular diode (D0) in the ground leg is a bad idea if you want to
have a common ground between the PIC and other external things.  If you
really want a series diode to protect against reverse polarity, put it in
the positive leg of the supply.

4 - Vdd and Vss are connected to the PIC backwards.  This is getting silly.
Didn't you check *anything* before posting this mess?

5 - The zener is accross the PIC+diode, not just the PIC.

6 - Note that a zener works as a regular diode in the forward direction, so
can also act as a clamp against reverse voltage.  Of course it has to be
installed in the right place and with the right orientation for that to
work.

So other than the 6 issues above in your 4-component circuit, it's fine.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2010\12\13@073940 by Olin Lathrop

face picon face
Isaac Marino Bavaresco wrote:
> 5) Don't use decimal points in the values of components. Use 5V1
> instead of 5.1V.
> 6) It would be better if your Zener diode were 5.6V (5V6).

That may be your preference, but don't tell someone they must do it that
way.  Personally, I find such notation annoying and more difficult to read.
I realize parts of the world use a comma instead of a decimal point, so you
may need to use your convention in some cases.  However, if the OP is doing
this for his own purposes, he's better off making it more readable for him
(and everyone else in his area which I think is North America).


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2010\12\13@075543 by Sarin Sukumar A

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part 1 760 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

On Mon, Dec 13, 2010 at 3:56 AM, Jason White <
whitewaterssoftwareinfospamKILLspamgmail.com> wrote:

> Hello, recently I have lost several ICs to reverse voltage and
> occasionally to overvoltage. I'm asking what would be the best
> configuration of diodes and caps to provide steady operation,
> overvoltage and reverse voltage protection to an IC ? I've attached
> what I think the circuit would look like, however I could be
> completely wrong ...
>
> Thanks
>
> Thats wrong. Circuit as in attached will work, You may add more filter and
decap capacitors if needed more regulation at the power supply

>
> --
> Jason White - C++ Programmer and Electronics Hobbyist
>
> -

2010\12\13@082232 by Jason White

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>>On 13/12/2010 12:56 PM, Jason White wrote:
>> Hello, recently I have lost several ICs to reverse voltage and
>> occasionally to overvoltage. I'm asking what would be the best
>> configuration of diodes and caps to provide steady operation,
>> overvoltage and reverse voltage protection to an IC ? I've attached
>> what I think the circuit would look like, however I could be
>> completely wrong ...
>
> I think
> - 5.1V for the zener could be too low, an 7805 for instance has a rather
> wide tolerance
> - the series diode is not needed, the zener is a normal diode too, so it
> would short a reverse power
> - I think I would add a series fuse or polyfuse
> - I would include some visual power indication, so you can see when you
> are applying the power wrong

I always include a reverse diode (aka "fools diode"). My way to prevent
overvoltage is to stick to 5V parts, and use only 5V as 'accessible
voltage' on my bench. Higher voltages (like 9-12V wall-warts) always
terminate in a barrel plug.

Thank yo

2010\12\13@084451 by Tamas Rudnai

face picon face
On Mon, Dec 13, 2010 at 12:36 PM, Olin Lathrop <.....olin_piclistKILLspamspam.....embedinc.com>wrote:

> 2 - There is no impedence shown for the zener to work against.  It won't
> take much of a power supply to blow out the zener if the voltage got too
> high somehow.
>

BTW: Not so long ago I plugged a wrong car charger into my Navman GPS and of
course something went off in it. Disassembling the device I have realised
they were using a very similar configuration described here, except there
was no D0 -- as when there is a reverse polarity the zener would clamp the
entire input to the Vdd rail anyway.

My best guess is that the designer have assumed that the fuse would blow off
faster than damaging other components inside the device, but he/she was
wrong. Actually I only had to replace that zener (and the fuse), however, I
do believe I was only lucky enough.

Tamas




{Quote hidden}

>

2010\12\13@085110 by Isaac Marino Bavaresco

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Em 13/12/2010 10:40, Olin Lathrop escreveu:
> Isaac Marino Bavaresco wrote:
>> 5) Don't use decimal points in the values of components. Use 5V1
>> instead of 5.1V.
>> 6) It would be better if your Zener diode were 5.6V (5V6).
> That may be your preference, but don't tell someone they must do it that
> way.  Personally, I find such notation annoying and more difficult to read.
> I realize parts of the world use a comma instead of a decimal point, so you
> may need to use your convention in some cases.  However, if the OP is doing
> this for his own purposes, he's better off making it more readable for him
> (and everyone else in his area which I think is North America).


I know it is personal preference, but there is some consensus about that.

One of my colleagues once sent a parts list to our Korean partners with
a resistor labeled 0.33R, they missed the decimal point and assembled
100 boards with a 33 ohm resistor instead.

Luckily I was in Korea at that time, and it took me several hours to
figure why the boards were not working properly. Even luckier, they
didn't assemble all the 1000 boards of the lot right away.


Best regards,

Isaac

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2010\12\13@090035 by RussellMc

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>> 5) Don't use decimal points in the values of components. Use 5V1
>> instead of 5.1V.
>> 6) It would be better if your Zener diode were 5.6V (5V6).

> That may be your preference, but don't tell someone they must do it that
> way.  Personally, I find such notation annoying and more difficult to read.
> I realize parts of the world use a comma instead of a decimal point, so you
> may need to use your convention in some cases.  However, if the OP is doing
> this for his own purposes, he's better off making it more readable for him
> (and everyone else in his area which I think is North America).

Demanding that people not say don't do risks re-entrant or recursive
flame wars :-).

5.1 V vs 5V1 is an old &  time honoured debate.

It is NEVER more "readable" to use eg 5.1V rather than 5V1. It MAY be
more familiar, comfortable,fit through burned in brainfilters etc.

A major reason for using 5V1 type nomenclature is that it is much
less prone to errors on hand drawn or worn machine drawn circuits. The
"." can be removed or rendered illegible with ease and can also be
easily enough added in error in various real-world situations. The
advantages are great enough as to be worth "biting the bullet" and
accustoming  one's brain to the different usage.


        Russell

2010\12\13@091550 by Kerry Wentworth

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It's easy to miss a decimal point, and put in a 51K resistor instead of a 5.1K resistor, especially if you are working from a copy of a copy.  I have switched over to the 5K1 style (for the most part).

However, it is not so easy to miss a 0.  Putting '0.33R' on a drawing SHOULD be enough to distinguish it from '33R', even if the decimal point is hard to see.  I would blame the Koreans for that one.

As a side note, beware of using zeners' forward voltage drop as a clamp.  Temperature compensated zeners, such as 1N851, don't conduct in the forward direction, at least not the way other zeners do.

Kerry


Isaac Marino Bavaresco wrote:
{Quote hidden}

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