I thought that current was the important factor in LEDs.
Does the LM7805 have a current range?

I would guess that the battery device is limited by the current from the AAA batteries - which may not be so for the 12V car system.

This may be a moot point, but as they say, a little knowledge is a dangerous thing. And my electronics knowledge is definately rusty.

Todd

 -------------- Original message ----------------------
From: vanagonvw <ac.vanagon@GMAIL.COM>
> Ed Duntz wrote:
> >
> > Is there an easy way to run 4.5 or 6 volt LEDs on 12 volts?
> Yep. Piece o' cake. :-)
>
> LM7805 is the base number for the part at Radio Shack. It can deliver up
> to 1 amp out, so depending on what you are doing, you need more than
> one, or a different device with more output capability.
>
> An LM317 is much the same, only it allows you to adjust the voltage out
> with a few resistors, if you want to be dead on 4.5V or 6V, but 5V will
> work fine in most cases.
>
> digikey.com or mouser.com have online data sheets that will show how to
> wire it up if you search for the part number. Calculate the max current,
> and make sure you use a heat sink if necessary, by the data sheet.
>
> Basically, you will just wire 12V to one pin, ground the gnd pin, and
> take the 5V off the third pin. May want to use filter caps on the input
> and the output, but its all in the data sheet.
>
> Lots of people around who can help. If you need more, just ask.
>
> John