The difference between the supplied voltage and the regulated voltage is
called the "head" voltage.  It will not necessarily be 2 watts regulator
dissipation for a head voltage of 2volts and drain of 1 watt.  It depends on
the type of regulator.  That is why switching power supplies have such high
efficiency.  I used some Maxim smart charging chips a few years back for
NiCad batteries.  They could withstand a large head voltage because they
were a switching device, similiar to a DC-DC converter.  I'm guessing the
78L05 is linear (they're pretty old and I'd have to look up the specs) and
cannot withstand a high head voltage.  There is certainly some more
efficient ways of doing it if efficiency is worth paying the extra money
for.  I used a very small DC-DC converter to field charge laptops off of
lithium batteries a couple of years ago and the price was not that high.
73,
Mike/ke6cvh

----- Original Message -----
From: "David VanHorn" <dvanhorn@CEDAR.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, July 22, 2001 5:36 PM
Subject: Re: [OT]: How to reduce power consumption for battery operated
circuits?


> At 07:26 PM 7/22/01 +0200, Kyrre Aalerud wrote:
> >The switching regs use ac don't they ?
> >If so, how would you run them from battery ?
>
> They use pulsed DC, and are perfectly happy running from batteries.
> --
> Dave's Engineering Page: http://www.dvanhorn.org
>
> I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here
> in my signature line, but due to the inability of sysadmins at TELOCITY to
> differentiate a signature line from the text of an email, I am forbidden
to
> have it.
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics
>
>

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