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Topic: 3w RGB color bar (BOM w/ TLC5940, Fets, UNL's (Read 4 times) previous topic - next topic



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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