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Topic: Basic info about a LED PWM "dimmer" circuit at ~3amps (Read 4 times) previous topic - next topic

tylernt

ironspider LEDs are so popular now that there is a wide variety of LED drivers to choose from. The easiest way to drive a bunch of LEDs is to get a driver with a PWM input, for example there are several models of BuckPuck and Meanwell drivers that have it. You just connect a PWM pin on the Arduino to the driver and dust off your hands.

Usually when driving a bunch of LEDs, you want to run at a higher voltage so you can run long strings of series-wired LEDs. 12V (for 3 LEDs per string) or 24V (for 6 LEDs per string) are popular choices. Generally you'll need one LED driver per string, because (except in rare circumstances) you should NOT wire LEDs in parallel.

What's your application? If your purpose is illumination rather than display of information, consider power LEDs. You can get the same amount of light from three power LEDs as you can from 100 little ones. The power LEDs will be cheaper to begin with (per lumen) and also easier to hook up (a single 12V supply, a single driver, and a dozen connections instead of 200+). Power LEDs also generally have more/better choices of color temperature. Only downside is power LEDs will require cooling via heatsink or fan.

dylantoymaker

""for example there are several models of BuckPuck and Meanwell drivers that have it. You just connect a PWM pin on the Arduino to the driver and dust off your hands.""

this is exactly what I want to do for a similar basic project.  do i need to connect the arduino ground to the negative in on the meanwell or buckpuck?  or do i really only need to connect the one PWM pin out the the Dim in?

thanks

tylernt


this is exactly what I want to do for a similar basic project.  do i need to connect the arduino ground to the negative in on the meanwell or buckpuck? 
In most circumstances, yes, you need to have all of your various components all connected to the same DC ground.

By the way I just discovered a neat thing about (some of) the BuckPucks. You can feed them whatever voltage you want for your LEDs (12 to 24V, typically), and get a nice 20mA 5VDC out on a "Ref" pin that can run your Arduino* -- no need for a second power supply. Convenient!

* I'm not entirely sure how many mA an actual Arduino Uno/Deci etc draws by the time you add the various other components on the board... it may be too much. But 20mA is plenty for a bare Atmega328.

Boffin1

#8
Nov 04, 2012, 08:08 am Last Edit: Nov 04, 2012, 08:13 am by Boffin1 Reason: 1
Instead of a wallwart, I would go for something like a Meanwell power supply ( say their RS-25-24 )  set to 25v output ( at 1.1 amps )   the output is adjustable from about 22 to 27 volts I recall .

They are pretty cheap here in South Africa, and I see they have  distributors in the US and UK.

You can wire up your 100  LEDs in 5 series strings of 20 in parallel ( if you say they all have resistors built in for 5 volts, you wont need other resistors )

Have a power mosfet to ground the cathodes  for the pwm.

You can feed a 5v regulator from the 24v ( a 7805 will take 35v )  and it will run at about 1/2 watt to drive an arduino.

These PSUs are stable driving pwm LEDs , I  PWM  5 amps to LED displays with no problem,  and if you do make a short circuit, the trip just hiccups until you remove the short.
With my mobile phone I can call people and talk to them -  how smart can you get ?

dc42


My completely inexperienced thought process was that I would need some kind of 5v voltage regulator capable of handling like 4Amps (since I imagine the $4 wall-wart PSu from ebay is not regulated), some caps to smooth that, a PoT, the ATtiny85, the LEDs and something (transistor? relay? MOSFET?) that can handle controlling these LEDs other than the ATTiny85?

Am I on the right track here?


Yes. The 5V power supply for the LEDs does not need to be well-regulated, but if it isn't then you should use a separate power supply for the Arduino. Use a logic-level mosfet to switch the LEDs from the attiny. There are lots of suitable mosfets, such as IRLU8726PBF.
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