[ell-i-developers] Re: Recommendations for MCU for Led driver?

  • From: otso@xxxxxxxxxxxx
  • To: ell-i-developers@xxxxxxxxxxxxx
  • Date: Wed, 4 Jun 2014 21:02:32 +0200

Thanks for everyone for input.

Eero: I'm designing an add-on to Ellduino, idea is to not spend every CPU
cycle on running SMPS. My driver will be powered through PoE.

Pekka: I'll focus on STM32F030's for now since we have experience of the
family in house and I'd rather bang my head against problems in
electronics than environment.

Jose: The PIC-microcontrollers are very interesting for their integrated
analog components and breadboard-friendliness, I'll check them out too
just out of curiosity.

Anyone interested in details of LED dimming: I found a few useful resources
http://www.lightbased.com/files/White_Papers/Facts_About_Dimming.pdf
http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/CD00213809.pdf

Interesting thing is that LED efficiency seems to go down as instant
current goes up, it might be worthwhile to have a SMPS which sets the
voltage in "general area" of bit more than forward voltage of LEDs and
then use PWM-dimming across a resistor.

As an added bonus it's easier to have higher resolution PWM control when
the frequency can be in range of 100 Hz rather than in 100 kHz-range.

On the downside, "current control" sort of does lose meaning. 500 mA at 20
%  duty cycle is not equal to 100 mA at 100% duty cycle for luminous
intensity. "Brightness control" would be a better value. I'll do some
research and get back on the subject.

-Otso

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