Low power LED driving

[shadow7]

I am trying to power one led (common 20ma variety, 3Vf) with a really small battery as efficiently as possible. I find myself lost in a sea of led driver ICs, buck-boost converters, 7555 designs, various low power oscillator designs...! The battery according to the manufacturer can be discharged at 100ma continuous or 150ma pulse, but its capacity is very low--10ma. Basically I am trying to make this battery light an led as long as possible with fair to strong brightness (thinking 10-30ma). I am sure there is some pulse or oscillation method or IC which should work.

 

[HarveyH42]

Search for 'Joule Thief' here or on the web. It's been very popular for the past couple of years. Pretty simple boost converter, very few parts. I've got 6 or 7 of them around the house, hook up any battery I used up in in stuff like remotes, alarm clock, even rechargeables, and get light for a few days. Even coin cells work, but usually not very long, but only tried 'dead' ones, don't know about new, might get a day...

 

[audioguru]

An LED needs power to light. If you oscillate the power on and off at a high frequency then the average power is low.
But your vision's response to brightness is also the average power so the LED will appear to be dimmed.

How about blinking the LED? Then it is turned off most of the time.
My Ultra-bright LED Chaser projects run for months on two or four AA alkaline cells.
The LEDs blink very brightly for a very short duration around and around, then pause before chasing again.

 

[shadow7]

Blinking

I actually tried the venerable LM3909 and yes, blinking would be a possible solution except that my project requires continuous or near continuous (triangle or other waveform may do) light.

 

[audioguru]

Continuous light from a bright LED quickly kills a little battery.
The step-up-the-voltage circuit wastes some battery power. Two battery cells in series would last a lot longer than twice as much as one.

 

[Boncuk]

Use a low current LED with a forward current of 2mA.

It increases battery life time considerably.