Need Help choosing products

Hello, my name is charles and I need a little help choosing products for a project of mine.

--- What i'm looking for is something that would ramp / increase intensity of leds on seperate channels automaticly after programming. --- What i'm running for leds is... (30) 1 Watt 350ma leds, I have them, 5 leds in series, then 6 series to parallel. --- My input voltage is 19v DC and if I calculated right my current draw is 2.1 amps total. If need be I could re-wire the leds for 12v and put a buck controller in to cut voltage. As of now I just have a cheap RGB controller to dimm them.

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How many separate channels do you want to control? The UNO has six pwm outputs which immediately gives you six pwm output channels. You'd need a driver circuit between the Arduino and the LED load, and there's a whole section of the forum dedicated to answering questions about that topic.

So you have 6 strings in parallel with 5 LEDs per string, and a 19VDC source? I would connect the top Anode of the string to +19, and use a good Logic Level, Low Rds, N-channel MOSFET to connect the cathode of the string to Gnd. 6 x 0.35A = 2.1A. For example, this low cost device: http://www.digikey.com/product-detail/en/NTD5867NL-1G/NTD5867NL-1GOS-ND/2401422

More here http://www.digikey.com/product-search/en?FV=fff40015%2Cfff8007d%2C1140050%2Cefc0005&k=n-channel+mosfet&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25

thanks for the replys.
(CrossRoads) you are correct. 6 strings in parallel with 5 leds per string at 19v. So if I wired it up like you mentioned
would that be considered the driver circuit like (PeterH) mentioned? Or do I still need a driver circuit?

So I would be able to make this work? I would like to get the board ordered.
The buck converter in the picture is for my cooling fan, led bubble wand, & 12v mini submersible pump, incase anyone was wondering.

Also I don’t mind reading - what section of the forum should I be looking in for what i’m trying to do, or does anyone have some links they would like to share.

I added a picture of the leds i’m using.

ProLight-1-Watt-Warm-White-LED.jpg

The MOSFET is the LED driver. Arduino pin to 150 ohm resistor to MOSFET Gate. 2.1A is not that much current.

weasel440: I would like to get the board ordered.

You are not going to order PCBs until you have the prototype functioning fully, are you?

weasel440: 6 strings in parallel with 5 leds per string at 19v.

How are you controlling the current through the LEDs? High power LEDs need a constant current source, not a constant voltage source. I suggest you use 4 LEDs per string (or whatever number you need to keep the total forward voltage to no more than 18V) and use a constant current driver circuit for each string. You can use the one described at http://www.pcbheaven.com/userpages/LED_driving_and_controlling_methods/?topic=worklog&p=3 (where Vdd is your 19V supply) with one change: connect the top end of Rg to the Arduino output pin instead of to Vdd, so that the Arduino can control the LEDs. The mosfet will probably need a small heatsink, since it will be dissipating (19 - 0.7 - Vf) * 0.35 watts, where Vf is the total LED forward voltage.

Paul__B:

weasel440: I would like to get the board ordered.

You are not going to order PCBs until you have the prototype functioning fully, are you?

My light fixture is functioning now. What i'm looking to do is make it ramp from 0 - desired intensity on at least 4 channels through a 8 hour time frame automatically.

dc42:

weasel440: 6 strings in parallel with 5 leds per string at 19v.

How are you controlling the current through the LEDs? High power LEDs need a constant current source, not a constant voltage source. I suggest you use 4 LEDs per string (or whatever number you need to keep the total forward voltage to no more than 18V) and use a constant current driver circuit for each string. You can use the one described at http://www.pcbheaven.com/userpages/LED_driving_and_controlling_methods/?topic=worklog&p=3 (where Vdd is your 19V supply) with one change: connect the top end of Rg to the Arduino output pin instead of to Vdd, so that the Arduino can control the LEDs. The mosfet will probably need a small heatsink, since it will be dissipating (19 - 0.7 - Vf) * 0.35 watts, where Vf is the total LED forward voltage.

I'm conrolling the current through a (RGB) dimmer for now, it's that little blue box in the photo in my first post. As for a power supply i'm currently using a laptop switching power supply.

Thanks for all the input so far. This is one of the subjects i'm not the brightest crayon in the crayon box, heck I might not even be in the box. :% I understand about all that i've built so far on this fixture, but trying to figure out how to add the arduino and make it work is making my hair turn grayer.

Ok, I guess where i'm lost at is... if my leds are calling for (about) 18.5v and the arduino has output of 3.3v & 5V or is there something i'm not reading correctly?

Thanks again for the help

If you use the constant current circuit that I linked to then you can drive the top end of resistor Rg from a 5V or 3.3V Arduino pin.

dc42: If you use the constant current circuit that I linked to then you can drive the top end of resistor Rg from a 5V or 3.3V Arduino pin.

Is this the only option or is there other ways to hook it up? At the end of the article it says "DISADVANTAGES:

Not very efficient since a lot of power is lost across the MOSFET"

It would be more efficient to use a switching regulator. There are ICs specifically designed to work as switching regulators for driving LEDs. However, as you are planning to use a relatively high supply voltage (19V) and connect several LEDs in series with each mosfet, the efficiency is not too bad. For example, if 16V appears across the LEDs and 3V across the mosfet, then the efficiency is 16/19 = 84%.

dc42: It would be more efficient to use a switching regulator. There are ICs specifically designed to work as switching regulators for driving LEDs. However, as you are planning to use a relatively high supply voltage (19V) and connect several LEDs in series with each mosfet, the efficiency is not too bad. For example, if 16V appears across the LEDs and 3V across the mosfet, then the efficiency is 16/19 = 84%.

Ok - ty. I tried setting this up so far to be as efficient as possible, plus keep the wattage up.

I picked up the arduino uno today, but it wil be a couple of days before I get a chance to get it mounted to my fixture =( - then I can start wiring it up. Trying to keep the look of the original top.

A question just to see if I understand how this will work... would the arduino act like a toggle / dimmer switch and the mosfets would act like a relay to handle the primary load to power the lights?

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