Harold Hallikainen wrote:
> We currently have several products running off an unregulated external
> 12VDC power supply (wall wart). Inside our product, we run through a
> 1N4001 for reverse polarity protection, then 1n LM7805 to regulate to +5V
> (to run the PIC!). Upcoming California Energy Commission regulations
> outlaw these external power supplies (due to lack of efficiency and
> standby power). We could replace these with 12V regulated switchers, but
> that is pretty inefficient. What I'd like to do is replace them with
> external 5V switchers, yet continue to allow the use of the old power
> supplies. It would be great if there were an LDO equivalent of the TO-200
> LM7805 with reverse polarity protection (so I could get rid of the diode
> and its drop). Anyone aware of a drop-in replacement?
> 
> THANKS!
> 
> Harold
> 
> 

Harold,

Try the LM2931 series from National.  Quote from the pdf:

Designed originally for automotive applications, the LM2931
and all regulated circuitry are protected from reverse battery
installations or 2 battery jumps. During line transients, such
as a load dump (60V) when the input voltage to the regulator
can momentarily exceed the specified maximum operating
voltage, the regulator will automatically shut down to protect
both internal circuits and the load. The LM2931 cannot be
harmed by temporary mirror-image insertion. Familiar regulator
features such as short circuit and thermal overload protection
are also provided.

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