You can make a 1st order sigma-delta loop with an op amp integrator, a comparator, a clock source, and a 1 bit DAC feeding back into the integrator.
Then, band-limit the pulse stream out of the comparator, and feed inot the mod port.
There's a problem with adding a gain element within the control loop. You would be adding additional gain and phase to what was a compensated system.
If you're not concerned with efficiency, put the LED in series as the upper feedback element, and a resistor from the LED to ground. The current...
