Surviving automotive load dump

[Jim Thompson]

Thanks martin, I hadn't seen these. These car manufactures standards
quote a maximum "load dump" spec of 60V (but I have seen 125V
mentioned elsewhere).

What is potentially scary... I observed around 400V in the early 60's
using a storage scope after blowing many alternator regulators
all-to-hell.

Have they improved alternators enough now that 125V is all you get ??

...Jim Thompson

 

[martin griffith]

What is potentially scary... I observed around 400V in the early 60's
using a storage scope after blowing many alternator regulators
all-to-hell.

Have they improved alternators enough now that 125V is all you get ??

...Jim Thompson

Yep a whole 10dB improvement in 30+years


martin

 

[Robert Adsett]

| In article <[email protected]>, Henry
| Kiefer says...
| > | Henry Kiefer wrote:
| > | > Winfield Hill wrote
| > | >>
| > | >> It's just a simple matter of power dissipation and thermal resistance
| > | >> vs. your maximum junction temperature spec.
| > | >
| > | > Some MOSFET specs specifiy a maximum Id regardless of other values.
| > | > So I'm not sure.
| > |
| > | Same thing, except that spec attempts to describe the maximum
| > | continuous power dissipation capability of the lead-bonding wires.
| >
| > Interesting. The problem is that the wire system is not specified in most datasheets.
|
| It's usually in footnotes along the lines of "total current limited by
| package"

Yes. Sometimes.

To place the problem a level higher:
If it is so, that MOSFETs cannot be burned if the bond wire is thick enough.

Nobody said that. Bond wires provide one limit on higher power devices
(high power being a relative term).

Why it is then, that sometimes Microcontroller pins
destroy to internal short if overloaded?

I don't know of any microcontroller I/Os that are high enough power to
make the bond wire limits relevant. The RDSon of the microcontroller
outputs is probably 3 orders of magnitude higher than that of a low
resistance 75V power MOSFET in a TO262.

Robert

 

[J.A. Legris]

What is potentially scary... I observed around 400V in the early 60's
using a storage scope after blowing many alternator regulators
all-to-hell.

Have they improved alternators enough now that 125V is all you get ??

...Jim Thompson

That's a different kind of transient from a load dump - higher voltage
but much less energy.

 

[martin griffith]

Hi,

As well as the usual spikes and brownouts, automotive systems have a
"load dump" condition, where the supply can e.g. rise to ~125 volts
for ~100ms.

What is the best way to protect against this? I need fairly low cost,
and small space (SMT). It must be a very common requirement, but all
I can find are some giant MOVs.

My best effort so far is a 4-transistor discrete "pre-regulator" to
stand-off the pulse (made from high voltage BJTs). Cheap in parts but
seems overly complicated.

Current would only be ~200mA, & must not drop more than a volt or two
during normal operation.

Any ideas?

more stuff
http://www.onsemi.com/pub/Collateral/HBD854-D.PDF
TVS/Zener Theory and Design Considerations Handbook


martin

 

[Joerg]

As well as the usual spikes and brownouts, automotive systems have a
"load dump" condition, where the supply can e.g. rise to ~125 volts
for ~100ms.

What is the best way to protect against this? I need fairly low cost,
and small space (SMT). It must be a very common requirement, but all
I can find are some giant MOVs.

My best effort so far is a 4-transistor discrete "pre-regulator" to
stand-off the pulse (made from high voltage BJTs). Cheap in parts but
seems overly complicated.

Current would only be ~200mA, & must not drop more than a volt or two
during normal operation.

Any ideas?

Talk to an automotive supplier. These switches don't seem to quite reach
your anticipated voltage levels but show some of the tricks of the trade:
http://www.infineon.com/upload/Docu...document_files/Application_Notes/reinmut2.pdf

Watch out for some peculiarties like turn-on during spike etc. It might
not be what you want.

Anyhow, I'd probably crowbar it out if it can be safely done in your
application.

 

[Nico Coesel]

Hi,

As well as the usual spikes and brownouts, automotive systems have a
"load dump" condition, where the supply can e.g. rise to ~125 volts
for ~100ms.

What is the best way to protect against this? I need fairly low cost,
and small space (SMT). It must be a very common requirement, but all
I can find are some giant MOVs.

My best effort so far is a 4-transistor discrete "pre-regulator" to
stand-off the pulse (made from high voltage BJTs). Cheap in parts but
seems overly complicated.

Current would only be ~200mA, & must not drop more than a volt or two
during normal operation.

Any ideas?

How about an NTC and a zener?

 

[Nico Coesel]

Hi,

As well as the usual spikes and brownouts, automotive systems have a
"load dump" condition, where the supply can e.g. rise to ~125 volts
for ~100ms.

What is the best way to protect against this? I need fairly low cost,
and small space (SMT). It must be a very common requirement, but all
I can find are some giant MOVs.

My best effort so far is a 4-transistor discrete "pre-regulator" to
stand-off the pulse (made from high voltage BJTs). Cheap in parts but
seems overly complicated.

Current would only be ~200mA, & must not drop more than a volt or two
during normal operation.

Any ideas?

How about an NTC and a zener?
I meant a PTC ofcourse

 

[Terry Given]

[snip]

Wow, what a great thread. Plenty of useful links, and it hasnt (yet)
denigrated into irrelevancy

Cheers
Terry

 

[PeteS]

[snip]

Wow, what a great thread. Plenty of useful links, and it hasnt (yet)
denigrated into irrelevancy

Cheers
Terry

Not sure if it's been mentioned, but load dump is covered in ISO 7637.

7637-1 covers 12V vehicles, and 7637-2 covers 24V vehicles.

Cheers

PeteS

 

[Joerg]

Actually, N-channel might be ideal for such occasions... tie the gate
to an R/C filtered version of Vout (A+ under normal conditions). Then
the transient will automatically turn off the device.

Wouldn't that punch a hole into it once the abs max gate voltage is
exceeded?

 

[Jim Thompson]

Wouldn't that punch a hole into it once the abs max gate voltage is
exceeded?

How can VGSmax be exceeded in such a setup?

The zener approach bothers me because large voltages CAN be developed.

Also, when the transient clears you run the risk of a large body-diode
current.

...Jim Thompson

 

[Joerg]

How can VGSmax be exceeded in such a setup?

Must have misunderstood you. If you had a "follower" in mind then it
can't be exceeded.

The zener approach bothers me because large voltages CAN be developed.

Also, when the transient clears you run the risk of a large body-diode
current.

Most automotive circuits I have seen used the transzorb scheme where
there was a huge device that shunts spikes to ground. Probably fine but
if people employ MOVs for that they have to keep in mind that there is a
finite number of spikes those can take.

What really surprised me was that in college I drove my old Citroen
without battery for years because 6V batteries were so expensive. Load
dumps galore. The nightmare for its little electric grid must have been
the huge compressor for the aftermarket trucker's horn I installed. Yet
nothing ever died.

 

[Jim Thompson]

On Tue, 16 Jan 2007 18:14:08 GMT, Joerg

[snip]

Most automotive circuits I have seen used the transzorb scheme where
there was a huge device that shunts spikes to ground. Probably fine but
if people employ MOVs for that they have to keep in mind that there is a
finite number of spikes those can take.

What really surprised me was that in college I drove my old Citroen
without battery for years because 6V batteries were so expensive. Load
dumps galore. The nightmare for its little electric grid must have been
the huge compressor for the aftermarket trucker's horn I installed. Yet
nothing ever died.

What? A 2CV ?

It probably had a GENERATOR with an electro-mechanical regulator.

Did it even have any accessories ?

...Jim Thompson

 

[Joerg]

On Tue, 16 Jan 2007 18:14:08 GMT, Joerg

[snip]

Most automotive circuits I have seen used the transzorb scheme where
there was a huge device that shunts spikes to ground. Probably fine but
if people employ MOVs for that they have to keep in mind that there is a
finite number of spikes those can take.

What really surprised me was that in college I drove my old Citroen
without battery for years because 6V batteries were so expensive. Load
dumps galore. The nightmare for its little electric grid must have been
the huge compressor for the aftermarket trucker's horn I installed. Yet
nothing ever died.

What? A 2CV ?

T'is the one.

It probably had a GENERATOR with an electro-mechanical regulator.

Yes. But the brushes were, well, marginal and I put a little wood stick
under the counter-weight of the regulator to provide more oomph for the
radio.

Did it even have any accessories ?

The original number of electronic components in that car was zero. Not
even a diode. But I had a shortwave radio in there, and a cassette
player, 6V-12V inverter and some other stuff.

I just had to make sure I didn't tap that truckers horn when idling or
the engine would stall. Same for the headlights and here the factory
must have anticipated such "frugal" usage because there was a handle
that could be reached easily like the turn signal. In France it used to
be customary to drive through cities with just the position lights on.

 

[Jim Thompson]

On Tue, 16 Jan 2007 18:37:11 GMT, Joerg

[snip]

In France it used to
be customary to drive through cities with just the position lights on.

'Twas so in 1994.

...Jim Thompson

 

[Joerg]

On Tue, 16 Jan 2007 18:37:11 GMT, Joerg

[snip]

In France it used to
be customary to drive through cities with just the position lights on.

'Twas so in 1994.

What really scared me was when a guy polished off a whole 700ml bottle
of Cote du Rhone with lunch, walked across the parking lot, hopped into
a 40-ton rig and fired her up.

 

[Jim Thompson]

On Tue, 16 Jan 2007 18:37:11 GMT, Joerg

[snip]

In France it used to
be customary to drive through cities with just the position lights on.

'Twas so in 1994.

What really scared me was when a guy polished off a whole 700ml bottle
of Cote du Rhone with lunch, walked across the parking lot, hopped into
a 40-ton rig and fired her up.

So ?

...Jim Thompson

 

[Joerg]

Jim Thompson wrote:

On Tue, 16 Jan 2007 18:37:11 GMT, Joerg

[snip]


In France it used to
be customary to drive through cities with just the position lights on.


'Twas so in 1994.

What really scared me was when a guy polished off a whole 700ml bottle
of Cote du Rhone with lunch, walked across the parking lot, hopped into
a 40-ton rig and fired her up.

So ?

Well, he didn't have a big lunch with it. Just a small sandwich plus two
or three hand-rolled Gauloises.

 

[Jim Thompson]

Jim Thompson wrote:


On Tue, 16 Jan 2007 18:37:11 GMT, Joerg

[snip]


In France it used to
be customary to drive through cities with just the position lights on.


'Twas so in 1994.


What really scared me was when a guy polished off a whole 700ml bottle
of Cote du Rhone with lunch, walked across the parking lot, hopped into
a 40-ton rig and fired her up.

So ?

Well, he didn't have a big lunch with it. Just a small sandwich plus two
or three hand-rolled Gauloises.

What is that----------^^^^^^^^^ ??

...Jim Thompson