I'm just finishing up my first electronics course (edx.org), and I want to build some LED grow lights for starting seedlings in the winter. I have high power LEDs, like this one here, and I have a PC power supply, which I think will be easier than trying to build my own AC to DC converter, at least for now.
But now I need to take the 5V input and do something to feed 1A to these LEDs. I asked a previous question here, before I realized that a transistor as a current source is a waste of energy. One of the answers to that question suggested a "buck converter with feedback and a current sense resistor". I don't know what this means. I just read about the buck converter, and I understand the basic idea. I drew a circuit at circuitlab
Now, how do I use feedback to control SW1 so that a desired current is flowing through the LED? In class we have learned about op amp feedback, and I think I could create a square wave pulse with an op amp, or 555 timer, or arduino, but I'm still lost. The only "current sensor" I know is a simple resistor, but if I put one in the path of that LED, I'm wasting energy again.
I will edit the circuit drawing and update the question if I get suggestions.