As with many other projects that control multiple LEDs, my system uses an LED matrix to control a maximum number of LEDs with a minimum number of inputs/outputs:

In my system, to get as high and controllable a current as possible, I use p-channel MOSFETs for the high-side switch controls (columns), and CAT4101 LED Drivers to control both the low-side switches (rows) and set the output current to a specific value:

This configuration requires 8 P-MOSFETs, and 8 CAT4101s. The P-MOSFETs are cheap at about $1 apiece. The CAT4101s are not so cheap - chip costs about $2.70 each, the breakout board about $2, and the trim pot about $0.50 (resistor and capacitor are trivial in comparison). That means a total cost of over $42 for all the CAT4101s. Plus, you have to set the current for each CAT4101 channel individually. That was my design decision right from the start in 2013, and I've stuck with it through multiple iterations.

Was lying in bed early one recent morning, and had a thought. What if I created a matrix with 8 N-channel MOSFETs controlling the low-side, and connected the source for all of them to a single CAT4101 chip complex that connects to ground? Something like this (shown for only one LED):

If it works, and I don't see why it shouldn't, it would have multiple advantages:

1. 7 fewer CAT4101s, for a savings of about $36. This partially offsets the $8 extra cost for the MOSFETs; a logic-level IRL540 costs about $1 apiece.

2. A lot less soldering associated with the MOSFETs than the CAT4101s. No need for a variable resistor, capacitor, 560R resistor, ground connection, etc. Just current inputs/outputs, gate connection, and a 10K resistor to drain off excess charge from the gate to ground when unbiased.

3. Far cheaper addition of more output channels (in a potential future design).

4. Far cheaper increase of output current capability by paralleling two CAT4101s together. In the current design, you'd have to double the total number of CAT4101s from 8 to 16, at an additional cost of about $42. In the modified design, you double from 1 to 2, which would double the max current to 2A at an additional cost of only about $5.20. This would require a PCB board to handle the extra current, as I don't think every current part of the system could handle the extra current.

5. Instead of having to adjust system current for 8 CAT4101s, you only need to set it for one.

6. The CAT4101 allows adjustment of LED intensity with PWM. I didn't include that capability with my original design, as it would have required a lot more connections to CAT4101s (and I was seeing weird interference effects when I tried it). With a single CAT4101, that becomes a practical option for controlling light intensity, far easier than adjusting current.

I definitely need to test this first on a breadboard with small matrix (2x2 or 3x3) to see if it works. If it does, I think I have most of the components necessary to build such a board, and it would plug into my current system with no compatibility issues. I'll keep you informed.