I'm trying to understand the circuit in figure 12, on page 6 of this data sheet -
http://www.onsemi.com/pub_link/Collateral/NSI45090JD-D.PDF'Dimming using PWM'
I want to use this constant current led driver with a ws2801 pwm driver (also cc) to allow me to control higher power leds with the ws2801, while retaining constant current functionality. I'm loaded with questions -
- What are the two resistors doing in this circuit, and how do I calculate their value?
- Am I right in thinking that while I can have an arbitrarily long chain of leds by supplying sufficient voltage, the maximum current through those leds (and therefore the ccr driver) can be 160mA?
- If need more current capacity than this, I see I can use 2 ccrs in parallel, which presumably will double this to 320mA. What is figure 11 illustrating then with the use of a resistor on one ccr? Is it used to set the max current to some value betwwen 160 and 320mA?
- If I need still more current than this, is there a better product or technique I could use? (bearing in mind the source is a pwm signal)
Thanks!