So ill try to make it short, 1st im not using an Arduino, im using Xport to PIC to send the data to the MAX7219, by OSC through MAX/MSP, just if u wondered, but im sure u can help me best! :) So im trying to light 4 high power (ca. 350mA each) leds with external power supply w the max7219, using darlington transistors as switchs. the Digits out of the max7219 goes to the Emitter, the SEG to the transistor Base, and the Collector to the power supply (w a ressitor). Now the thing is that the stabilty of the whole thing is very ISET dependent, and i dont understand why. First I had to change the ISET ressistor to 1.3 megaohm(!!!) for the thing to work at all, and also then it works with 3 leds simultaniasly but when i light 4 of then it all crashes and i gotta reset the ic's. Now even if its possible to calculate the right resistor for the ISET, I still wanna use the same max driver for more normal leds, and w 1.3Mohm i dout ill get a nice light...
My only guess was that all the current from the LED's sinks into the max7219 DIG pin, and thats the core of the problem.
I had another idea to escape this problem, and it by using a quad switch ic, so with a control pin i switch a gate and then could sink the current straight to ground. Anyone knows of such chip???