I have been looking at some electronic load circuits. I would like to have a circuit that uses a MOSFET that pretends it is a high wattage fixed resistor. My application is a homemade RC relaxation oscillator EDM machine. Since I am experimenting, I don't know what resistance value I am ultimately going to need so I would like to make it adjustable. I also wanted to try my hand at coming up with something more elegant than using light bulbs as power resistors. I have a few questions about circuit 1 that I copied from an internet source.

Is the math correct for circuit 1? To behave like a fixed resistor I=V/R. V+ = V * R1/(R1+R2) and V- = I *** Rs V+ = V- V *** R1/(R1+R2) = I * Rs I = V / (Rs(R1+R2)/R1)) R = Rs(1+R2/R1)

Suppose that I want the circuit to behave like a fixed 20 ohm, 200W power resistor for example. What would be logical choices for Rs, R1, and R2? A source that I have been reading says to make R1>>Rs. What does the >> mean?

I believe that Rs should be a very low value to keep the I^2*R power dissipation down. Also it would have to be less than the total resistance that the circuit is trying to mimic in the first place. Is this true?

Why is the R1, R2 voltage necessary. Why wouldn't circuit 2 work?

Also there was some mention of adding an RC to the output of the op amp to prevent oscillation. Could someone provide more details on that?

Why wouldn't circuit 2 work?

Is the math correct for circuit 2? To behave like a fixed resistor I=V/R. V+ = V V- = I *** Rs V+ = V- V = I *** Rs I = V/Rs R = Rs

NEVER MIND! Rs would have to be the power resistor that I am trying to have the circuit mimic in the first place.

Any help would be greatly appreciated. Thanks