ATM DIY LED Flashlight Conversion

[espector@mlswc.uk.lucent.com]

Richard wrote:

>I sure don't want to use a resistor or current limiter: I would end up
>wasting a lot of power.  What happens if you charge a small capacitor and
>then connect it (through a fet) to the LED?  Perhaps you do no damage if the
>capacitor is small enough.  And the brightness is proportional to the
>frequency.
>
>Another method might be to build up a current through an inductor, then
>switch the LED into the current path.  

You are heading towards the invention of the switch-mode power supply. As
you correctly say, a series-connected LINEAR device to limit diode current
will waste power. This applies to both a simple resistor and to an integrated
regulator chip. 

However, don't lose sight of the fact that your LED is taking only a few
milliamps (say between one and ten). This is considerably less than a normal
incandescent bulb requires, hence the battery will last longer. So, don't 
worry about the wasted power due to current limiting/regulation - unless you 
really do need to squeeze every last drop of capacity out of your batteries.

Regards

Edwin.