amateur here... I want to switch a load through a MOSFET, approximately 200vdc with a 3amp resistive load, . If the source voltage drops I would also like to step down the current, ie if it hits 100v, I may want to drop current to 1.5amp. I dont need it to be linear, but rather just select a desired step level in my sketch, ie at 125v step to 2amp, at 100v 1.5amp, etc, in 2-3 steps.
I plan to drive the 10v gate with an optoisolator, with a 1k resistor across gate/source.
What is the best way to step my current down?
Should I PWM it, or is there a concern of MOSFET switching speed or gate heating?
Or can I lower the gate voltage to get a lower source current (I think this may increase resistance/heat on the gate=bad)?
Or do I need to build a separate circuit leg for each current level I desire, ie 3 current levels means I need to use 3 mosfets of 3 different io ports and switch one off, then the next step gets switched on. The switching speed does not matter to me, and the circuit can be paused/interrupted while switching to ensure complete discharge of the drain.
A requirement is to lower the source current, I do not really care what the load is seeing for current, so I do not want to burn off current as heat, that would still be using similar source current but showing less to the load, this is not what I want.
The mosfet I have chosen is IRFP460C, spec sheet: https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/IRFP460C.pdf
thank you kindly for any pointers.