One other problem that crops up with this approach is the fact that the load is not tied to ground. You can move the sense resistor, but then you have to have a tight supply voltage, else the amp sees supply fluctuations as current changes.

I used a similar circuit for the Variable message signs project we did last year, but that needed a very sneaky input circuit to fool the MAX7221 into thinking that it was driving a ground connected single RED LED, not a bank of 100mA pulsed LEDS.

My mistake was to use a Bipolar device that was out of spec for the pass transistor, we lost around 30% of the opamps before I realised what had happened. In the field,, or more accurately 10metres up in the air on a ladder.

Steve

Steve