If the lamps that Ed wants to use are designed for 4.5 to 6V operation,
they already have current-limiting built in. Heck, running them right
off 12V might not even overcurrent them, but there's no way to know for
sure without knowing more of what's in the package.

--

Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR

On 9/17/2007 12:37 PM Todd Last wrote:

> 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
>