Efficiently Dropping Voltage: What's the Best Method?

[couchsurf]

Looking to drop a 10v Li-on battery to 6v DC. What is the most efficient way without to much wasted power. Adjustable voltage regulator? diodes?,
something else? needs to be small. Thanks

 

[berkeman]

What do you mean by most efficient? All of the power of the drop will be lost unless you are willing to do a switching regulator.

The simplest way would be to us an adjustable linear regulator of the appropriate power rating. The LM317 is the jellybean part that is used for this application:

http://www.national.com/pf/LM/LM317.html

You can make a circuit with a power transistor and two resistors, to give you some fairly stable voltage drop, but it varies with temperature a little bit, and is not as stiff as using the LM317. And the two options are about the same in size.

Remember that you need to dissipate that heat somehow, and keep it away from the battery itself. Use appropriate heat sinking or some other option to get rid of the heat.


EDIT -- fixed typo "power resistor and two resistors" -> "power transistor and two resistors" (jeeze)

 

[chroot]

Switching regulators are not really any more difficult to use than linear regulators. For most applications, switchers are perfect.

- Warren

 

[couchsurf]

The application it will be used for is a bike light. 6v 15w bulb, the battery is a 10.8v 3.6 Ah that is doing nothing right now. I figure a burn time of about 2.5 hrs with this if I get it down to 6 volts. Because its on a bike I wanted to keep it small. Also thinking about a digital controller. Efficiency? I didn't want to have the 4 extra volts being turned into heat vs. getting a longer run time from the battery, but I'm not sure what is possible.

 

[Uncle Shorty]

I found an old 6volt resistance unit on the fire wall of a junked car. For years I used it to step down twelve volts to six volts for small radios on the sailboat. It worked great!

 

[marcusl]

A well designed switching power supply is typically over 90% efficient. <EDIT: took out sentence here..> Take a look at National's LM5005 regulator datasheet, which includes circuits.

This is a fun project, but if you are looking for an easy approach then buy a bike light!