On Tue, 1 Apr 2003, Mark Belanger wrote:

> I have a small battery charger for a portable electronic device that I'm
> trying to wire into the car power system.  Unfortunately, it takes 9V.
> I know I can run it off the 12V if I want to give the battery a short
> life, but how can I bring down the 12V to 9V?  Is it as simple as
> soldering  one of those cheap 3-pin voltage regulators?

If the current is fairly low you can do this.  Most 3-terminal regulators
are good for a few hundred milliamps with no heat sink, or up to 1.5 amps
with one.

You probably won't find a fixed 9V regulator, but if you buy an LM317
variable voltage regulator you can use a fixed resistor network to set it
at 9V.  Or you could try using a 7805 fixed 5V regulator and lifting the
ground pin 4 volts above actual ground with a couple of red LEDs in
series.  As a side benefit the LEDs can serve as a power light.

David Brodbeck, N8SRE
'82 Diesel Westfalia
'94 Honda Civic Si