Arduino Controlled LED Lighting || Transistor Choice Help

Thread Starter

-live wire-

Joined Dec 22, 2017
912
I am working on a project where you control the color, brightness, and and pattern of an RGB LED through an Arduino Nano. I have programmed it to output 3 variable PWMs (R, G, B of the LED) based on what you select through a rotary encoder. This works well. However, I want to use brighter, higher power LEDs.

I am going to use an old printer charger that can supply 31V at 2.4 amps (and thankfully has short-circuit protection) as the power supply for the RGB LED. I suspect that there is actually a max of 2 amps, so just to stay on the safe side, I am not going to try to power anything that draws more than ~1.5A.

I could use some help choosing the components to scale it up and finish this project.

I need help finding an RGB LED that has the following characteristics. A lot of the things are hard to look for, and for some things you just don't know until you buy it. So suggestions would be helpful.
-All colors are very bright (but not so much so that it temporarily blinds you if you look into it, anything less is ok).
-It disperses light well (so maybe 120-180 degrees).
-It mixes colors well and has good-looking colors (unlike very cheap RGB LEDs you might buy in bulk).

-It draws no more than 1.5A at 31V (so 45W).
-The forward-voltages of all the colors are about the same.
-It does not require special constant-current or other drive circuitry, and has clear common gnd, R, G, and B. Essentially I don't want to have to do anything too complicated to power it. I do not really care if the component life is shortened by using constant voltage, as long as I don't have to constantly replace it. I do not really plan to use it a ton.
-It is not to hard or expensive to get a heat sink for it, and one would ideally be built in.

-It must be, of course, RoHS.

I also need help choosing a switch to control the high-power LED through the Arduino. Mechanical relays would completely fail, and solid-state ones would probably do pretty poorly too. Those PWMs for the LED go up to ~10 kHz. However, transistors, like MOSFETS or IGBTs or BJTs, have the necessary switching speed. But there are so many choices, and some of them require a lot of external circuitry.

Which kind of transistor requires no more than 20-40mA gate to collector to act as a closed mechanical switch (low fV, saturation resistance), requires little to no external drive circuitry (maybe just a resistor or two), can handle up to a few amps at over 31V, and will not be difficult to heat sink? Essentially I am looking for the most Arduino compatible one that can also handle the printer charger power. Some suggestions would be great, thanks.
 

philba

Joined Aug 17, 2017
960
First, your requirements are somewhat contradictory. Bright but not blinding, for example. I have LEDs that run off 20 mA and can be painful to look directly at. You can directly drive those LEDs from an arduino so they must not be bright enough for you? Maybe if you stated your actual application it would be easier to help you.

Drivers are simple, lots of them out there. Look up "NPN LED driver circuit" on google.

Your power supply seems an odd choice. I'd first figure what LEDs and then select an appropriate power supply. You are definitely putting the cart before the horse here. You might be able to adapt the one you have but start with the LEDs and drivers first,

Consider LED strings. You can achieve almost any level of illumination by increasing the string length. Look at Neopixels from Adafruit to learn about this stuff. Directly drive from the Nano.

Finally, you should learn a little about illumination - candellas, foot candle, lumens. Also understand the role of diffusers.
 

ElectricSpidey

Joined Dec 2, 2017
1,648
I could suggest some nice LEDs that would work with that supply...but not with those requirements.

They blend nice, come mounted on a nice heat spreader (you still need a sink) but mostly come with a common anode not ground? (what is a common ground LED?)

120 degrees

Very bright, but they will hurt your eyes if you look directly at them...as with just about any high power LED.
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
My bad. I meant common gnd. So I'll take a look at the LED strips. So what kind of transistor would work best with the Arduino?
 
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