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Topic: 3w RGB color bar (BOM w/ TLC5940, Fets, UNL's (Read 11385 times) previous topic - next topic


Jan 30, 2013, 02:08 am Last Edit: Jan 31, 2013, 01:07 am by sjim Reason: 1
I want to make fixtures with 6 3w RGB's (3.5v blue/green and 2.5 red @350ma) and wanted
to use this preprogrammed mini 3ch RGB controller-below, some say they wouldn't go over 2amp per channel. Could this be
done and what parts (TLC5940, npn, mosfets(p/n), LM317s, constant source/sink...etc) would I need for such as small wash color bar.
 I could forego the mini controller but would need a build to support pwm.

mini RGB controller:

These are the RGB's (look to be common anode)

I seen posting below, is this a viable solution to using the TLC to get 350ma per channel ?
"I used ULN2003 TransistorArrays (they are just about 70cent for 7channels) and 1W resistors to get enough current through.
The ULN2003 needs inverted signals on the base, so I used 74HC04 HexInverter to get the right HIGH and LOW signal."

-------Also---- but how do I connect a pwm device or RGB controller to this-----
Could using these below be one possible solution for the drivers?


The 'mini RGB controller' is common-anode, 12V, 4A per channel.

You need some way to limit the current through each LED.  You could use series resistors:

For each blue and green:
12V - 3.5V = 8.5V across the resistor.
8.5V at 350 mA = 24.3 Ohms  (call it 25)
8.5V * .35 A = 3W  so you will need resistors rated 3W or more.

For each red:
12V - 2.5V = 9.5V across the resistor.
9.5V / .350 A = 27.1 Ohms  (call it 28)
9.5V * .350 A = 3.3W  so you will need resistors rated 3.5W or more.

Six LEDs, each drawing 350 mA is 2.1A, well within the stated 4A-per-channel limit.

As an alternative to the series resistors you could use a constant-current regulator PER-LED.  The LM317 adjustable voltage regulator can be wired as a constant-current source.

If you had separate R, G and B LEDS you could put several in series and need only one resistor for each series string:

For three blue or green in series:
12V - (3*3.5V) = 1.5V across the resistor.
1.5V / 0.35 A = 4.28 Ohms  (call it 5)
1.5V * 0.35 A = 0.525W  so you will need resistors rated 1W or more.
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I'm wondering how well the LM317 can do fading..etc  I found this circuit that looks like it would work really well, although the mini 3ch RGB controller uses programmed modes with pwm and so I don't know how these two will work together, perhaps, it will work fine.  I'd like to consider using TLC5940 or Mosfet N or P, but don't know exactly what the MOD/layout would be for either (at this moment) and if could still use mini 3ch controller.



I know the TLC5940 can only do 120ma per channel 16 which is 5 RGBs but I'd have to mosfet p (I believe) do regulate current before entering the TLC, does this sound right?  It would be more feasible to just do 5 RGBs(3w) per fixture and therefore only needing single TLC per fixture, however, wouldn't I need a mosfet per color so in this case 15 of them?

I suppose you must run these 4pin 3w RGB in parallel?  or could it done in series?

What need to find is several circuits used with high voltage/current LED drivers..etc



check out the top post on the thread I linked above written by David (DC42), I'm using a TLC in that config and it drives LED strips nicely :)

The TLC will not source 120mA per channel with them all active, I think it can only source 120mA max between all channels, its only a small IC at the end of the day so to have almost 2A running through it would produce magic smoke. You could use big resistors to regulate the current or a driver such as http://www.diodes.com/datasheets/ZXLD1360.pdf and use the PWM signal from the TLC to control the dimming on the ADJ pin - if you read through the whole thread I linked to it will become clearer.


Thankyou... I tried following the threads (gets a bit confusing for me) not great at reading circuits, moreless better at drawlings ,lol.   I'll look up the ZXLD1360 and do some learnings about it.  If I do use the TLC  it would give me multiplexing capabilities or individual control over each RGB within fixture (nice to have), but, could go either way.  Have you used the ZXLD1360  ?     


yes I'm using some ZXLD1360's in some Halogen replacement LED bulbs and the Tlc can control the brightness

check out this post (and the attached schematic) for the way to connect them up, let me know if I can clarify anything!


Feb 01, 2013, 06:33 am Last Edit: Feb 01, 2013, 07:43 am by sjim Reason: 1
After look up the ZXLD1360, that's exactly what I need... (also HV9910 possible supposedly), would need one per 3wRGB.  Do you have a drawling of your circuit available, what parts would I need besides the 1360 and 5940, capacitors, resistors..etc  for 350ma per ch for each RGB?  Would the flow go as folllows:  12v(power) > 1360 > TLC5940 > RGB led  and/or what pieces hang off of any of these?   R1, R2, uf's...etc

Thank you, this will be such a big help!


Sorry I forgot to post the link! http://arduino.cc/forum/index.php/topic,139792.msg1052456.html#msg1052456 (drawing of the circuit I used attached).

The 1360 datasheet should show an example circuit also for working out its support components.

it would be more like

Microcontroller > tlc > 1360 > led


I have built constant current drivers for a 10W RGB LED and it runs for hours quite happily. See here http://arduino.cc/forum/index.php/topic,134827.0.html
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following Riva's tutorial for a constant current driver, I just finished the prototype for a 10W 350mA RGB LED. works great with PWM and the parts
were relatively cheap. For each channel: a simple NPN transistor, a Logic level mosfet, two resistors. Per channel maybe ~1.5£. The most expensice was the 12V wall PSU that I had to buy.


Would there be any advantage to use this circuit below using ULN2803's ?  Would only need 2 x 2803's  vs 15x1360's (3 per RGB for 5 RGB fixture) is that correct?  My concerns are is performance change w\ multiplexing...etc.  You can reach 300ma with 3v on the 2803's if you look at the spec sheet.



I did order a few 10w RGB, once I get the 3wRGB driver figured out I'l just change to accommodate the 10w...  I'm new into this but tech enough and detailed so that it's pretty fun doing so....


Posting my learnings here today,

Just discovered WS2803D (in place of the TLC) and it's datasheet says it can handle up to 12V directly so no need for the NPN's in some cases, can drive 6RGB's per chip, serial interface

Here quick breakdown I could use for either 5-6 RGB3w fixtures:

WS2803 = 18 channels (1 IC needed)
TLC5940 = 16 channels (2 IC = 32 channels)
74HC595+ULN2803 (pair) = 8  ( 3 pairs of IC = 24 channels

Using the WS2803 chip (or chips) you don't use PWM to talk to them but a form of serial using 2 digital pins. These 2 pins will talk to all the WS2803 chips (not 2 pins per chip) as there control pins are daisy chained together CKI > CKO & SDI > SDO   (not sure I understand this yet)

The VCC pin on the WS2803 needs connecting to the +5V pin on the UNO and the GND pin needs connecting to the GND pin on the UNO and to the 12V ground. The CKI and SDI pins need connecting to a couple of the UNO's digital pins as these program the WS2803 chip(s).
The IREF needs connecting to the shared ground (preferably not ground through the UNO as I'm not sure of IREF output level)
A couple of capacitors to just reduce potential electrical noise and smooth out loads. I would try one 16V 10uF electrolytic and one 16V 100nF ceramic per WS2803 connected between VCC & ground close to the WS2803

I need to learn more about the high current output of this 2803D IC... sounds like a possible upgrade from the TLC


I need to learn more about the high current output of this 2803D IC... sounds like a possible upgrade from the TLC

"WS2803 has 18 output channels, each channel can output up to 30mA constant current." Two more channels but 1/4 the power on any single channel.

As far as price goes the TLC5940 can be had for just as low or better price than the WS2803.


I used that rgb mini fader with those 3watt rgb led's it works great just add a resistors ....

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