ws2801 with higher voltage leds

Other Hardware LEDs and Multiplexing
1

Can anyone shed some light on how to use higher voltage leds (or more leds chained together) than the ws2801 is normally spec'd for?

There is a schematic and description of this on page 10 of the datasheet here http://www.adafruit.com/datasheets/WS2801.pdf but I'm not sure how to calculate the value of the two resistors (RB and RXFB).

Also if I used a transistor with the ws2801 to increase the current capacity, what would be the implication of losing the constant current feature? My rough understanding of this is that as the led heats up the current flowing through it will change slightly, and may vary between different leds but I don't have an idea of how much of a problem this will be. If it is a problem, is there a better way to increase the current capacity of the ws2801? (to use high power leds or motors)

Thanks guys

2

mrboni:
Can anyone shed some light on how to use higher voltage leds (or more leds chained together) than the ws2801 is normally spec'd for?

There is a schematic and description of this on page 10 of the datasheet here http://www.adafruit.com/datasheets/WS2801.pdf but I'm not sure how to calculate the value of the two resistors (RB and RXFB).

There is no 'RXFB' in a high voltage application, only constant current as it acts as the feedback loop for the WS2801. In high voltage applications, there is no feedback loop (it's grounded.)

That same page has the formula needed to calculate RL, as well as what VCE and RB are. You should know what VDD is (in that example it's 24V), and you should know what your VLED is ...