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I want to use either WS2811 or WS2801 to drive high power LEDs with spacing between LEDs up to 15 meters. These are going to be used outdoors or in a water feature. As you know WS2811 output is constant current but WS2801 output can be constant voltage, I've come up with the following circuit to drive power LEDs constantly at about 350mA (R_load).

schematic

simulate this circuit – Schematic created using CircuitLab

I'm no EE, is the circuit ok? any suggestions to make it better?

Considering the distance between LED's will it work if I use 74hc125 buffer IC to "power up" the data signals of WS2811 (or WS2801) ICs?

WS2801 uses SPI but WS2811 uses I2C, which one is better for my case?

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2 Answers 2

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I Thinks it better to go with WS2801 and you can implement the below circuit for your application.

enter image description here

Need to take some special care while selecting the Transistor Q1. Since the requirement is to flow 350mA of current so its better to select the transistor which can carry arround 500 mA of current.

Resistor R1 is used to set the current limit and this doesn't depends on the voltage supply VDD. The equation for this can be given as

R1=0.7/Required current.

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  • \$\begingroup\$ Thanks for your reply. But this circuit inverts the signal. When the output signal of WS2801 is low the LED should turn on but in this circuit its reversed. \$\endgroup\$
    – ahmadx87
    Commented Sep 25, 2015 at 6:11
  • \$\begingroup\$ yes it will invert the signal. But as per requirement you can change the output PWM format in WS2801 itself. For example if the required format is 0101, configure WS2801 to output as 1010 \$\endgroup\$
    – Sanjeev Kumar
    Commented Sep 25, 2015 at 6:15
  • \$\begingroup\$ Yes! hadn't paid attention to POL pin. What about the data connection? is SPI better for longer distances? WS2801 requires 2 wires for data but WS2811 just 1. \$\endgroup\$
    – ahmadx87
    Commented Sep 25, 2015 at 7:12
  • \$\begingroup\$ Datarate of SPI is higher than that of I2C. So here you have a wide range to play with the datarate of SPI.Start at the highest rate, see if it works. If so, done. If not, slow down clk rate and recompile the code. \$\endgroup\$
    – Sanjeev Kumar
    Commented Sep 25, 2015 at 7:32
  • \$\begingroup\$ where is R1? what is R in R1/2R? \$\endgroup\$
    – Vishnu Mohan G
    Commented Jul 30, 2016 at 14:47
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Here is something I recently worked on. Simple, low cost and fully tested. It will work with many SPI controllers out there such as Holidaycoro, Kutop, DMX-SPI, SD-RAM SPI, and LOR-Controllers. enter image description here

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  • \$\begingroup\$ yes it is similar to my solution, but using barely a resistor to limit the current is not a good idea, high power LEDs are better to be driven using a constant current driver. \$\endgroup\$
    – ahmadx87
    Commented May 1, 2016 at 10:14

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