I want to control 3 RGB 5050 LEDs with single WS2801 chip on a 12V. I know I need to use 5v zener diode, resistor and a filter cap to make chip work with 12V supply. Although, few things concern me:
- Should connect resistors to GFB/RFB/BFB (feedback) pins? As datasheet says, resistors on these pins are used to control current output. If I do not need control of output corrent, I can leave them float or I should connect them to gnd?
- How to connect LEDs? What about limiting resistors on LEDs? I can’t use resistors. As far I know, there are two options:
a) Connect LEDs in series. I have seen this type of connection on LED pixels. There are 2caps, diode, resistor and extra 3 resistors as current limiting ones for LEDs. (e.g.)As I see from WS2801 datasheet, max. output voltage is 7V. If min. voltage for 5050 led is 2.8V, 3 leds in series give 8.4V and that exceeds 7V(red should work fine, right? 1.7V*3 = 5.1V). What are these limiting resistors for in that case?
b) Connect single LEDs to chip’s output. In that case, every LED would require each own 3 limiting resistors, resulting in 9 extra resistors which does not seem as great solution.
Basically, I’d love to hear corrections/suggestions on things I have wrote up there. I believe they are not all correct.
I have attached a schematic at my current stage of develop.
p.s.: here’s link to datsheet