Three 3w lights - power supply?

Alright so I'm a bit of a newbie when it comes to circuts and arduino, but I'm planning on hooking up three 3w lights up and I'm wondering about a powersupply to use.

The Specs of the lights:

Forward Voltage: 3.2-3.8V Forward Current: 750mA

So what kind of power supply should I use? (Also if someone could tell me the formula they used to figure it out so I know for future refrence)

Also the transistors for the lights I'm going to use are the TIP120's (Does that sound fine? or do you have a better reccommendation?)

Thanks.

Leds have to be driven by a constant current source. This can be as simple as a series resistor but that gives you low efficency and is mostly suitable for low power leds for indication purposes and currents of about 20mA. For high power/high current leds as those you describe a switching current source is recommened. Google arduino high current led

Yea, I plan on setting up something like this

https://www.youtube.com/watch?v=AePn1gAd5gc

But see how the power supply is hooked on the lower left corner of the bread board? I'm trying to figure out the type of power supply i would need there.

Thanks.

The tip120 would give a voltage drop of about 1.4v So if you just use a 5v wall wart you wouldn't even need any series resistor.

So I want to individually control each 3w LED, so from other videos I’ve seen they have 1 transistor per 3W LED. So are you saying a 5v ~2a would fully light up all the leds? (sorry if that made no sense I’m trying)

dogrin17: So I want to individually control each 3w LED, so from other videos I've seen they have 1 transistor per 3W LED. So are you saying a 5v ~2a would fully light up all the leds? (sorry if that made no sense I'm trying)

3 x 750ma=2.25 A so it would get pretty close.

I believe this is what the guy in the video has done. That is not the proper way to do it, he is relying on the inner resistance of the circuit to limit the current

You can build a constant current source from an LM317 Adjustable Voltage Regulator. Build three of those set for 750 mA and use them to feed the LEDs. Put a transistor or MOSFET switch between the LED and Ground. Then you can use about any voltage over 5V. If you use a 7V 3A supply it can provide power to the Arduino as well.

there are lots of sites about using LED's

you do not say if you are going to control each separately or if they will all be on at the same time.

if they are all the same LED, you can wire in series or in parallel.

in series, a 12v power supply could work. higher voltage, lower current power supply That would have them light all at the same time with one pin. not sure if they would all dim exactly the same,

in parallel, you start with a lower voltage, higher current power supply.

it sounds like you want to create your own power supply for this ? would you be starting from a 120v AC line or 220V AC ? what part of the world are you in ?

if you say you will start with a DC power source then just get the right one the first time.

johnwasser: You can build a constant current source from an LM317 Adjustable Voltage Regulator. Build three of those set for 750 mA and use them to feed the LEDs. Put a transistor or MOSFET switch between the LED and Ground. Then you can use about any voltage over 5V. If you use a 7V 3A supply it can provide power to the Arduino as well.

Lm317 can pass up to 1.5A. At 750mA you need 2v over the output voltage. A heat sink will be necessary.

Weedpharma

you can by an LM2596 adjustable power supply from e-bay for less than $10

LM317 Constant current source schematics

Thanks for all the help guys,

johnwasser: You can build a constant current source from an LM317 Adjustable Voltage Regulator. Build three of those set for 750 mA and use them to feed the LEDs. Put a transistor or MOSFET switch between the LED and Ground. Then you can use about any voltage over 5V. If you use a 7V 3A supply it can provide power to the Arduino as well.

Thanks for all the help guys, but I've been looking over these posts for about an hour and I'm lost. I've downloaded a few arduino simulators, and I'm trying to replicate what you just said. The sim didnt have a mosfet, so i just replaced it with a different transistor. Is the sketch even close to what it should look like or am I absolutely miles off?

Or could something like this be done, (instead of the strip it will be the 3 lights)

When you do a drawing, try to keep the red and black wires for power supply only. In this drawing you have used both red and black for the supply then used red for an output, this can cause confusion

I assume all 3 mosfets should be wired the same as the lower one. Otherwise looks ok.

Weedpharma

weedpharma: When you do a drawing, try to keep the red and black wires for power supply only. In this drawing you have used both red and black for the supply then used red for an output, this can cause confusion

I assume all 3 mosfets should be wired the same as the lower one. Otherwise looks ok.

Weedpharma

Alright, thank you. One more question, sorry. So if my three LEDs are going to use up 2.25a, I need a power supply with 3amps, but I dont know how many volts to get. I've got a heatsink to put on the voltage regulator, so should I do something like 5v 3a or 9v 3a?

weedpharma: I assume all 3 mosfets should be wired the same as the lower one. Otherwise looks ok.

Weedpharma

by this, I assume you mean to put the resistor on the signal line.

dave-in-nj: by this, I assume you mean to put the resistor on the signal line.

Quick look did not actually look at the R value. Assumed was high value to discharge gate capacitance to turn off quicker. On looking again, I see what you mean.

1k resistor in series with gate not absolutely essential but well advised.

Weedpharma