AIR NatSemi had an app note on this, I think in conjunction with their
LM293x series regulators, which aim ti keep themselves and your load alive
in an auto environment.

Load dump, reverse battery, alternator spike, ...

TI data sheet

        http://www.ti.com/lit/ds/symlink/lm2930.pdf


* Reverse Battery Protection
* 40V Load Dump Protection
* Internal Short Circuit Current Limit
* Internal Thermal Overload Protection
* Mirror-Image Insertion Protection

See data sheet for more

ONSEMI

* 60 V Load Dump Protection
* -50 V Reverse Transient Protection
* Internal Current Limiting with Thermal Shutdown
* Temporary Mirror-Image Protection

Designed primarily to survive in the harsh automotive environment,
these devices will protect all external load circuitry from input fault
conditions caused by reverse battery connection, two battery jump
starts, and excessive line transients during load dump. This series also
includes internal current limiting, thermal shutdown, and additionally,
is able to withstand temporary power-up with mirror-image insertion

http://www.onsemi.com/pub_link/Collateral/LM2931-D.PDF


             Russell
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