overvoltage protection (5V /12V DC)

ferent voltages. 5V, 12V, 24V, 48V? and all get power from the standard

9mm power plug. (I think it?s 9mm?) I wondering if there is a simple way to do over voltage protection so that if some one plugs a 12 V supply into a 5 V unit it doesn?t fry it. Yeah I?ll do a bit of internet searchin g too.

Check out Microsemi's app note AN-31 for one possibility.

Den mandag den 27. januar 2014 17.52.43 UTC+1 skrev George Herold:

ferent voltages. 5V, 12V, 24V, 48V? and all get power from the standard

9mm power plug. (I think it?s 9mm?) I wondering if there is a simple way to do over voltage protection so that if some one plugs a 12 V supply into a 5 V unit it doesn?t fry it. Yeah I?ll do a bit of internet searchin g too.

-Lasse

ifferent voltages. 5V, 12V, 24V, 48V? and all get power from the standar d 9mm power plug. (I think it?s 9mm?) I wondering if there is a simple w ay to do over voltage protection so that if some one plugs a 12 V supply in to a 5 V unit it doesn?t fry it. Yeah I?ll do a bit of internet search ing too.

Got it, thanks... that's sort of the brute force approach. (Even I could h ave done it :^) I wonder if I have to worry about reverse polarity too. O r is center postive pretty much standard these days?

George H.

On Monday, January 27, 2014 12:09:21 PM UTC-5, Lasse Langwadt Christensen w rote:

ifferent voltages. 5V, 12V, 24V, 48V? and all get power from the standar d 9mm power plug. (I think it?s 9mm?) I wondering if there is a simple w ay to do over voltage protection so that if some one plugs a 12 V supply in to a 5 V unit it doesn?t fry it. Yeah I?ll do a bit of internet search ing too.

Sweet! Thanks Jim... ahh Lasse

George H.

We use a polyfuse (radial, not surface mount) and a unidirectional transzorb.

(It'd be real nice if the same voltages had the same plugs.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

y to do over voltage protection so that if some one plugs a 12 V supply int

ng too.

orb.

Hmm OK, so the transorb conducts fast, and then the poly fuse opens to 'sav e' the transorb? That would be easy to hack into place.

Thanks, Geo

Right. The transzorb does reverse polarity protection, too.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Nice idea, but the opamp (LM397) is spec'd for only 30V. Also watch or the max VGS of the FET,

It will blow up at your 48V.

--
Reinhardt Behm

Hmm... So my attempt at analyzing this circuit...

So, is M1 simply to protect from reverse voltage? The gate would be positive in regards to the source, which would shut it off? Though it

this work? Or does it only protect to -8v?

Then, DZ1 shunt is configured to have about 5.3v, which will saturate Q1 when it reaches 5.3v, which will then bring M2's gate to V1, which will shut it off M2.

So, when voltage is > 5.3v, the current is rerouted through R5.

Though, I would expect Q1 to only go into saturation once V1 reached

5.3+.75v, or 6v. That isn't what the graphs show.

At 5.5v, there would be ~.2v to Q1's base, through 1.1k?, so it would be .18mA current. With a current gain of 30 @1mA, that would be ~5mA through R5. Ah ha!, 5ma * 1k = 5v, so it would drop enough. So it doesn't need to get to saturation.

Is that about right?

Thanks, Daniel.

An input spike or overvoltage will blow out the M1 gate.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

with different voltages. 5V, 12V, 24V, 48V? and all get power fro m the standard 9mm power plug. (I think it?s 9mm?) I wondering if there is a simple way to do over voltage protection so that if some one plu gs a 12 V supply into a 5 V unit it doesn?t fry it. Yeah I? ?ll do a bit of internet searching too.

df

does

d be

yes M1 is reverse protection, first body diode then turned on. You'd want to put a zener on the gates to limit GS voltage

Checking you math I'll let Jim do ;)

-Lasse

When did people start using "M" for MOSFETs instead of "Q"?

Best regards, Spehro Pefhany

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Den tirsdag den 28. januar 2014 01.24.09 UTC+1 skrev Spehro Pefhany:

e way to do over voltage protection so that if some one plugs a 12 V supply

rching too.

pdf

it's a spice thing

-Lasse

Lasse beat me to it... I was out on a "save-the-day" gig today >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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I love to cook with wine.     Sometimes I even put it in the food.

I'm too busy right now... you do it >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

not with those parts at 12V

What's a good mosfet for withstanding 48V V_gs and threshold low enough for 5V operation?

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Anything over +8V will exceed the Vgs abs max rating of 8V.

It should cope with negative excursions down to -12V due to Vds abs max rating of -12V.

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Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

Cool. Here we have an overvoltage protection circuit that is blown out by the overvoltages it's supposed to protect against.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

fferent voltages. 5V, 12V, 24V, 48V... and all get power from the standard 9mm power plug. (I think it's 9mm?) I wondering if there is a simple way to do over voltage protection so that if some one plugs a 12 V supply into a 5 V unit it doesn't fry it. Yeah I'll do a bit of internet searching too .

df

will needs zener clamps on the gates as well

maybe something like this?

DF

-Lasse