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Topic: Clean and energy efficient LED dimming (Read 4 times) previous topic - next topic

MrGlasspoole

Hi,

after searching through the web i found out that it seams that dimming LED's
is not so easy. There is more then PWM with a mosfet involved.

By clean i mean things like i can read here:
http://joost.damad.be/2012/09/dimming-12v-led-strip-with-mosfet-and.html
http://jeelabs.org/2011/11/8/fixing-the-arduinos-pwm/

Then i found this cool site - Highly Efficient 0-100% LED Dimmer:
http://www.opensourcepartners.nl/~costar/leddimmer/
But this is for 20mA LEDs

So i need a dimmer for 12 Volt LEDs up to 15 Watt.
Is there a way to modify the "Highly Efficient 0-100% LED Dimmer" and use it with
the Arduinos PWM?
Would it make sense?

dhenry

I think it is nuts for people to go into so much details just to control leds.

Having said that, one of the responders to the first link correctly identified the reason for ringing when switching a mosfet. That becomes a bigger issue when an inductive load (a motor for example) is being switched. I discussed that in one of my posts a couple days ago.

The last post's approach is excessively complicated. You can have a dedicated pwm controller to switch leds - those dc/dc converters with on/off pins are great for this.

Alternatively, you can use your arduino to perform conversion: you can use a sampling resistor + the analog comparator for cycle-by-cycle control; or you can use the sampling resistor + adc for averaging. The 2nd approach is very computationally intensive.

MrGlasspoole

To much detail?
Hm, but nobody wants flickering lights in the living room?

Also the cables to my sleeping room ans bathroom will be around 10-20 meters.
In the moment everything is open - but when the wallpaper is done it's to late to change
something. So i need to make sure everything is planed correct and thats the reason
i read allot.

So what will be the best solution for my 12 Volt house lightning where everything can be dimmed?

DVDdoug

Some high-power LED power supplies will accept PWM or variable DC as a dimmer-control signal.   You can filter PWM to variable-DC, but sometimes it's a 0-10V control so you'd have to amplify the Arduino's 5V output.  Most of these supplies are highly efficient.

PWM is 100% efficient (in an ideal world), but in addition to (or along with) dimming, you need current limiting.   With low-power LEDs, you normally use a resistor for the current limiting, and that's not efficient, but no big deal if you are only wasting a few milliwatts.    In fact, switched current-limiting (very efficient) is usually based on PWM with feedback-control and a "smoothing" inductor.

Quote
Is there a way to modify the "Highly Efficient 0-100% LED Dimmer" and use it with
the Arduinos PWM?
Probably...   But, by the time I figure-out how that circuit works and how to modify it, I dunno...   

Quote
To much detail?
Hm, but nobody wants flickering lights in the living room?
As long as they flicker at a fast rate, nobody can see it.  Older flourscent lights flicker at 2 x the 50/60 Hz line frequency.   TVs flicker at the same rate.  Film flickers at twice the framerate (2x24Hz).   Most people aren't bothered by that.  Newer flourscents with electronic ballasts flicker at kHz frequencies and nobody is bothered by that.   The Arduino's default PWM rate is ~500Hz, and nobody can see that either.

DVDdoug

#4
Dec 21, 2012, 02:21 am Last Edit: Dec 21, 2012, 02:31 am by DVDdoug Reason: 1
Quote
In the moment everything is open - but when the wallpaper is done it's to late to change
something. So i need to make sure everything is planed correct and thats the reason
i read allot.
I'd say try do make it easy to access the wires or run new wiring.  If you have an attic or crawl space, that's not hard to do.  Otherwise, maybe you can run some conduit.  It's very-likely that something will need to change in the future.

And, it sounds like its a little late to be designing some new-untested lighting concept.  For something permanent in your house, I'd consult an electrician and install something tried-and-true.  You can buy dimmable and non-dimmable LED home lighting that runs off 12V or 120/240V, and as far as I know it's all highly efficient so you shouldn't need to design something yourself unless you really want to.

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