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How can I use a 6 Volt power source to power a 5 Volt USB port and a 1 Volt LED? Answered

How can I use a 6 Volt power source to power a 5 Volt USB port and a 1 Volt LED?  I know I need a regulated voltage for USB, but how can I get the remaining power to go to the LED?

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JaredsProjectsBest Answer (author)2010-02-20

Use a 7805(5v regulator) to regulate the voltage for usb, and power the usb from that and split it off to a 7801(1v regulator) for the led.

AI

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frollard (author)JaredsProjects2010-02-20

This is pretty much it. 

My confusion is...ARE there 1v leds?  I know infrared is the lowest at around 1.5...  most leds would barely glow with 1 volt.

Other thought:  With only 6 volts to work with, get a "LOW DROPOUT" regulator - regulators usually need an overhead of 1.5+ volts to burn off to ensure they regulate the 5 volts accurately.  The ones I'm referring to can be extremely efficient because they run a smps that uses exactly the power needed and no more...

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Validis (author)frollard2010-02-20

Yes, there are 1V LEDs, I found some at my local electronics store, I didn't know there were any myself, until I asked them.

Thanks for all your help, both of you. :)

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frollard (author)Validis2010-02-20

I would love to see one of these!  I still want to see them.

On digikey the smallest I can find is 1.5v
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=524729&k=led

infrared emitters:  smallest is 1.2v
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=524328&k=led

Are you SURE?

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johnathon007 (author)frollard2010-02-26

"Use a 7805(5v regulator) to regulate the voltage for usb, and power the usb from that and split it off to a 7801(1v regulator) for the led"

7805 is rated for 7-35 input but will it work with 6v ? im trying to do something similar with a kid car battery to power several usb devices.

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frollard (author)johnathon0072010-02-26

It will probably be insufficient unless as I say you get a low drop regulator whose input is closer to 5.1-20 to regulate 5.0 volts.  A basic runofthemill 7805 won't do it reliably.  Remember a fully charged 6 volt battery might put out upwarsds of 7ish volts, but it'll be not very well regulated, and will drop below 5, or even cutoff unpredictably.

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