MAX 7219 LED Driver 7 Segment LED Question

A few quick questions, I'm looking at the datasheet for the MAX 7219 LED Driver (found here: https://www.sparkfun.com/datasheets/Components/General/COM-09622-MAX7219-MAX7221.pdf) which controls 7 segment led displays. I'm specifically interested in the R-SET value table shown at the top left of page 11. This table tells you what resistor value (in kilo ohms) your resistor should be to limit the current to your LED displays.

1) What if your LEDs operate at a larger voltage than the one listed? Would it be safe to use the smallest resistor value (under the 3.5V column) shown for the appropriate current? (I'll be using LEDs that operate at 3.7V).

2) Since every segment of 7 segment LEDs use two LEDs in series where as the decimal point (DP) uses only one LED (half the voltage) is it safe to assume that choosing the correct R-SET value for the 3.7V segment LEDs will not kill the decimal point LED? How can you control this if R-SET is the only resistor that can control current limiting?

3) If the answer to the above question is: "No, you cannot use a resistor value for both the 3.7V segments and 1.7V decimal point," then If I never turned on the decimal point (I don't need the decimal point), can I just use an R-SET value for 3.7V? Thanks.

  1. Yes.
  2. Follow the example in Figure 2. You could use another LED instead of the zener.
  3. Yes.