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Thursday, January 19, 2012

DIY 9-18 series leds constant current driver

When my desk lamp died I decided it's time to upgrade it to led desk lamp.
I have several 8mm straw hat leds which are laying around unused for too long. So I thought to put those into lamp mod. Then I thought about how to drive these leds with as little power wasting as possible and come across to constant current drivers. Yes I can power leds with series resistors to limit current, but there is power wasting in resistors and I can't drive each leds with the same current. In this project I wanted to learn something about boost converters and opamps, this means I'm going to do a constant current driver with voltage boost converter to power many leds in series. That way I can keep the same current on all leds in the module.
I took ATtiny13A + some generic opamp and made it.

Shematics looks like this:

To test it I've made a pcb with generic white 5mm 9 leds in series and drive them with 20ma (ajustable in fw):

Yes it may look ugly, but it works. Push button is for changing power modes in final design. I've tested it on 9 leds in series with output around 27.5v and on 18 leds in series with output around 58v, works fine with not much current to leds.
Actual lamp mode and source files next time.