White LED Driver? Efficient?

okjello

Newly Enlightened
Joined
May 4, 2006
Messages
1
I have a bunch of white led i want to run to make a light for a camp. This would be 12 source most likely a UPS type battery. A friend told me you can use a LED driver to essentially switch the led really fast to save power?

Can anyone tell me where to find such chip? Or any other info would be great.
I was thinking about using 12 leds and driling holes into a 1inch thick peice of lexan with a lightly frosted (sand blasted)

Thanks
Mark
 

greg_in_canada

Flashlight Enthusiast
Joined
Jun 7, 2004
Messages
1,146
Location
Saskatoon SK Canada
Welcome to CPF Mark.

You may not need a driver at all if you have a 12V battery. If you connect 3 LEDs in series the voltage drop across them will be about 11 volts when they are driven at their rated current. So then you just need a resistor to "use up" the other 1 volt. If you are putting 20mA (=0.02 Amps) through the LEDs then the resistor you need is 1/.02 or about 50 ohms. Depending on the particular LEDs and the actual battery voltage you may need more or less. It is better to start with too much (say 100 ohms) and then measure the current and adjust as necessary.

Make 3 duplicates with your other 9 LEDs and you are done. The LEDs will dim as the battery voltage drops but I think the gel cell batteries are pretty flat (voltage wise) as they discharge.

If the dimming isn't acceptable then a driver that regulates the current flow is what you want. I don't have any suggestions on what driver chips are best. Some else here will though :)

(Using a resistor you are wasting some power but with 11/12th of the voltage going to the LEDs you aren't wasting too much, only 8 or 10%.)

Greg
 
Last edited:

Builder

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Joined
Feb 14, 2005
Messages
66
okjello said:
I have a bunch of white led i want to run to make a light for a camp. This would be 12 source most likely a UPS type battery. A friend told me you can use a LED driver to essentially switch the led really fast to save power?

Can anyone tell me where to find such chip? Or any other info would be great.
I was thinking about using 12 leds and driling holes into a 1inch thick peice of lexan with a lightly frosted (sand blasted)

Thanks
Mark
It's called Pulse Width modulation and it is used to dim LEDs. Google for "PWM LED" and you'll find all sorts of chips.
 
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