- I have a power supply rated for the right voltage and current, but it only allows me to set a voltage, not a constant current. I need to design a circuit and program that will read the current passing through the load (that will vary with time) and make adjustments to the voltage to keep the current as constant and as close to 20A as possible.
Yes, I get that you want a constant current source. What I don't get is why you're trying to design and build your own. They aren't especially expensive to buy and will probably be cheaper than the Arduino you'd be using for your DIY one. For example, LT3741 can handle 20A at 6V and you can buy them individually for a few bucks. Do you actually need
to 'design a circuit and program' to solve this problem?