Good video to explain many things. But for LED I'd recommend to implement simple ConstantCurrent self-oscillating buck using comparator LM393 it's faster than OPAMP. Using 2 SMD BJTs and 1 N-MOSFET still could be cheaper than using specialized IC, simpler but of course less to explain :)

I did one some time ago as well! In the end I did it with a uC and digital control loop, since I needed multiple channels. Especially if you already have an MCU in your project you could even save money with it. And for certain higher powered, or very low powered LEDs it sometimes does make sense. The chips can sometimes be awfully specific.

Good job! Efficiency could be improved by using a FET instead of a BJT (logic level FET if Vcc is this low), and by using a lower impedance driver such as a totem pole for the FET's gate to get it to switch faster. A Schottky diode would reduce the amplitude of the undershoot and also improve efficiency with its lower forward voltage. You could also improve your Vcc filter capacitance/placement to reduce the drop in Vcc when the transistor is on. The ringing after the diode turns off is there because you're operating in discontinuous conduction mode (DCM). It's not normally a problem, but if the amplitude of the overshoot or EMI are problems you may be able to use a snubber or clamp. DCM is the right choice for this low power circuit anyway. Yes, I know this is just a demo circuit. Just thought this might answer some questions.

Very cool, a bit over my head, but i'm still enjoying this.

Love your videos friend :) have nothing else to say but thanks they are very well explained and interesting

*Where's the part 4 of "DIY Digital Lab Power Supply"?*