Go Down

Topic: 3w RGB color bar (BOM w/ TLC5940, Fets, UNL's (Read 4 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.
Send Bitcoin tips to: 1L3CTDoTgrXNA5WyF77uWqt4gUdye9mezN
Send Litecoin tips to : LVtpaq6JgJAZwvnVq3ftVeHafWkcpmuR1e


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.

Go Up