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Topic: 3w leds 400w ATX PSU (Read 1 time) previous topic - next topic

Stuart Faust

if i wanted to drive 5 with the series resistor , and wanted to dim them whats the best method of doing this?

Im thinking of brightness adjestment if there too bright with a pot perhaps
dimming via the arduino on a timer for on and off daylight times etc?

could i run 10 2 sets of (5 in series) in parallel and dim the lot?

using http://led.linear1.org/led.wiz

18.5v , 3.4 , 700 and 10
gives me 2 stings with 2.2ohm and would need just over 1w 2.2ohm resistor.

this i would use for my main white lights and the odd colour

this i would want to dim if too bright

then i would run 5 for my blues.

This would all be duplicated on the other half of the tank.






dc42

As I said before, I wouldn't recommend running 5 of them in series with just a resistor. Try calculating the series resistor using that wizard. Then change the supply voltage by 0.3V to allow for imperfect regulation, or change the LED forward voltage by 0.1V each, and see how much the current changes.

You could drive two strings of 5 using a one mosfet and one BJT per string as a combined on/off control and constant current driver. Then you could feed them both from 1 or 2 Arduino PWM pins to do PWM dimming.
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Stuart Faust

hi , if i use a

http://www.ebay.co.uk/itm/400542207152?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

and run 2 rows in parallel of 3 leds setting the current to 1.4a and voltage to 12v that should work right running from 1 of the 12v lines?

then could i dim these using something like this?

http://www.ebay.co.uk/itm/140928585939?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Thanks

Henry_Best


hi , if i use a

http://www.ebay.co.uk/itm/400542207152?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

and run 2 rows in parallel of 3 leds setting the current to 1.4a and voltage to 12v that should work right running from 1 of the 12v lines?

then could i dim these using something like this?

http://www.ebay.co.uk/itm/140928585939?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Thanks


There's no need for any dimmer or pot.
Use the PWM outputs on your arduino to control the brightness.
5th time lucky?

Stuart Faust

where would i link it in?

would i use it to control the voltage going into the leds from the constant current regulator?

so

12v -> cc/cv -> ardiuno -> leds

if is is the arduino going to like 1.4a multiple times?

Henry_Best


where would i link it in?

would i use it to control the voltage going into the leds from the constant current regulator?

so

12v -> cc/cv -> ardiuno -> leds

if is is the arduino going to like 1.4a multiple times?
Feed the PWM signal into the base/gate of the transistor/MOSFET controlling the 12V to your LEDs.
By varying the mark/space ratio of the PWM signal, you vary the brightness of your LEDS. The arduino isn't supplying the LEDs, the 12V is. All you're doing is switching (through the transistor/MOSFET) the 12V on and off very quickly using a very low current at 5V.

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