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Topic: WS2801 & WS2803 (Read 937 times) previous topic - next topic

powertek

I have ordered a few samples of these chips but have a couple of questions.

The WS2801 requires 3 separate resistors to set the current. If I wanted to use one of these chips to drive an RGB LED strip, I would take the 3 outputs of the chip and use it to drive 3 MOSFET's. Since the strips are already current limited, do I still need to use the resistors ?


In regards to the WS2803, to use this chip with RGB strips I would do the same as above, however, does it make much difference which pins go to which color ? ie. If I had 6 RGB LED's could I take all the Red lines and run them to OUT1-OUT6, the Blue to OUT7-OUT12, and the Green to OUT13-OUT18  or do the have to be RGB, RGB, RGB, etc. ?

KirAsh4


The WS2801 requires 3 separate resistors to set the current. If I wanted to use one of these chips to drive an RGB LED strip, I would take the 3 outputs of the chip and use it to drive 3 MOSFET's. Since the strips are already current limited, do I still need to use the resistors ?


Essentially you'll be doing the same thing as Figure 8 in the datasheet.  You can ground the XRFB pin with that setup.  You just have to set RL to the appropriate current for the MOSFET.  The formula is on the same page.


In regards to the WS2803, to use this chip with RGB strips I would do the same as above, however, does it make much difference which pins go to which color ? ie. If I had 6 RGB LED's could I take all the Red lines and run them to OUT1-OUT6, the Blue to OUT7-OUT12, and the Green to OUT13-OUT18  or do the have to be RGB, RGB, RGB, etc. ?


Remember that you are the one sending the data, so whether you send data in RGBRGBRGB or RRRGGGBBB or GBRGGBBRR format, the IC doesn't know nor care.  It will simply display whatever you told it to.

powertek

Thanks for the reply. I either missed seeing Figure 8 or forgot it was there. Silly me. The MOSFET's I'm using are NXP SI2302DS. They come in a SOT-23 package and are capable of sinking up to 2.5A each. So there should be plenty of current to run several RGB LED's.

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