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'[EE] Automotive transient protection'
2007\11\09@102941 by David VanHorn

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I'm having trouble finding solutions for transient protection on the
automotive DC bus.

I need to find something that will work on a 24V system, and ideally
also on the new 48V (or 56 or whatever they are calling it) consumer
automotive bus.

I can't use regulators with built in protection, I need this external.

Can someone point me in the right direction?

2007\11\09@124604 by Dwayne Reid

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face
At 08:29 AM 11/9/2007, David VanHorn wrote:

>I need to find something that will work on a 24V system, and ideally
>also on the new 48V (or 56 or whatever they are calling it) consumer
>automotive bus.

Quick question: I thought the new consumer automotive power supply
was a nominal 42V (3x 12V batteries in series).  Has that changed?

My standard input & load-dump protection circuit is a series diode
followed with a series 47R 5W resistor.  The clamp is a P 1.5KE-33
(or 30V, depending on the regulator) transzorb.  That works for me
because most of my stuff runs on 100mA or less.

That's been working reliably for many years in both automotive and
industrial (24V) applications.


The exception to that is our DC fan controllers - I use devices that
are rated to at least 100V in the power-handling section.  Means that
I have to use more devices in parallel than I would if I were to use
lower-voltage parts but that's the price I pay for reliability.  Note
that the control section in those controllers still uses the series
resistor and transzorb clamp.

As I've mentioned in the past, the absolute worst load-dump situation
I've had to deal with was a 24V (nominal) earth-moving machine in a
coal mine.  The external lighting was about 100A - the 24V buss
jumped to about 80V for almost 100ms when the lighting was switched
off.  I had assumed at the time that the only reason the voltage
didn't go any higher was that one or more of the rectifier diodes in
the alternators (2 of them) was breaking down.

Regarding the upcoming 42V supply: I'm waiting to see what new
regulators become available before I tackle designing for load-dump
and transient conditions.  That, and doing measurements on an actual
vehicle when I see one.

dwayne

--
Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2007\11\09@130603 by James Holland

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face
> Date: Fri, 9 Nov 2007 10:29:39 -0500
> From: "David VanHorn" <.....microbrixKILLspamspam@spam@gmail.com>
> Subject: [EE] Automotive transient protection
> I'm having trouble finding solutions for transient protection on the
> automotive DC bus.
>
> I need to find something that will work on a 24V system, and ideally
> also on the new 48V (or 56 or whatever they are calling it) consumer
> automotive bus.
>
> I can't use regulators with built in protection, I need this external.
>
> Can someone point me in the right direction?
>
>

What sort of transients and surges do you have to protect against? I've done
a number of designs for 28V military vehicles. The usual circuit is a high
side switch that turns off before the max. regulator input voltage is
exceeded. On the input side of this is an LC filter (primarily for EMC) and
the output side has a TVS to catch the fast transients. The circuit is
designed to handle 100V for 100ms and 250V for 1uS. It helps to have an
automotive regulator on the input to the equipment because it raises the
voltage at which you have to turn off the circuit and gives more flexibility
with the TVS voltage.
I would expect that there are off the shelf filters for regular automotive
applications. Have you tried Vicor or XP Power?
Cheers
James


2007\11\09@155444 by David VanHorn

picon face
> Quick question: I thought the new consumer automotive power supply
> was a nominal 42V (3x 12V batteries in series).  Has that changed?

42V, that's the one.

> My standard input & load-dump protection circuit is a series diode
> followed with a series 47R 5W resistor.  The clamp is a P 1.5KE-33
> (or 30V, depending on the regulator) transzorb.  That works for me
> because most of my stuff runs on 100mA or less.

I need roughly 100W here. :(


> As I've mentioned in the past, the absolute worst load-dump situation
> I've had to deal with was a 24V (nominal) earth-moving machine in a
> coal mine.  The external lighting was about 100A - the 24V buss
> jumped to about 80V for almost 100ms when the lighting was switched
> off.  I had assumed at the time that the only reason the voltage
> didn't go any higher was that one or more of the rectifier diodes in
> the alternators (2 of them) was breaking down.

That's useful to know. I'm expecting the 24V vehicle systems to be the
worst environment.
Sounds like the 42V system won't me much (any?) noisier than the
existing 12V systems.

2007\11\10@133907 by PicDude

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face
Don't have the specs with me now, but look at that RBO-40 (ST Micro).  I know
Mouser carries it.

Cheers,
-Neil.


On Friday 09 November 2007 09:29, David VanHorn wrote:
> I'm having trouble finding solutions for transient protection on the
> automotive DC bus.
>
> I need to find something that will work on a 24V system, and ideally
> also on the new 48V (or 56 or whatever they are calling it) consumer
> automotive bus.
>
> I can't use regulators with built in protection, I need this external.
>
> Can someone point me in the right direction?

2007\11\10@184749 by David VanHorn

picon face
> What sort of transients and surges do you have to protect against? I've done
> a number of designs for 28V military vehicles. The usual circuit is a high
> side switch that turns off before the max. regulator input voltage is
> exceeded. On the input side of this is an LC filter (primarily for EMC) and
> the output side has a TVS to catch the fast transients. The circuit is
> designed to handle 100V for 100ms and 250V for 1uS. It helps to have an
> automotive regulator on the input to the equipment because it raises the
> voltage at which you have to turn off the circuit and gives more flexibility
> with the TVS voltage.

Basically I'm trying to come up with a design that will handle lots of
"improvised power" sources, including the full range of probable
vehicle power.  Humvee would be the normal source, but I want to allow
as much lattitude as I can.

The high voltage cutoff is a given, but I remember seeing something
like a two or three terminal device for this.  I sort of miss the days
of data books when I have these problems.  I hate playing "guess the
category" on web sites.

2007\11\12@043425 by Alan B. Pearce

face picon face
> I can't use regulators with built in protection, I need this external.
>
> Can someone point me in the right direction?

I did post a link some time back to a Linear Technology chip designed to
help with this.

Check out the LTC4356-1 chip, and possibly related devices mentioned at the
end of the datasheet.

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