I'm curious about the application circuit shown in figure 2 of the MAX7219 datasheet to drive display units that have a high forward voltage (typically 3-5 LEDs in series for each segment).
The circuit leverages +5V and -5V power supply rails, so that the segment high side can be driven directly by the 7219 segment sources, while the digit cathodes (low side) are pulled to -5V using a MAX394 and a MOSFET. This seems overkill, because even with all segments on, at a 30 mA segment current it's still just 210 mA to sink. I wonder if a much simpler construction for the low side would work such as this one:
(the pulse voltage source representing the digit output of the 7219).
Even conservatively assuming all 7 segments continuously and simultaneously lit, the 210 mA would remain well within spec for a 2N2222.
