I'm trying to create a variable wattage heater circuit as shown below. I'm clearly not a trained electrical engineer (simply a hobbyist) so please forgive my crazy idea and general stupidity. You can imagine R1 as a light bulb or a toaster, or whatever you like. The goal of the circuit is the idea that you can replace R1 with a heating element with a resistance of anywhere from 0.05 ohms (uncommon), to 0.1-0.3 ohms, and control the wattage of the heating element to be something like 150-250 watts by only partially turning on the MOSFET via a voltage regulator at the MOSFET's gate.
(power is supplied by two high-drain Li-Ion batteries in series. yes this is a lot of load for these batteries, but yes they can handle it in pulse situations.)
I've built a few prototypes, and as some of you have probably already guessed, I keep blowing MOSFETs. I've been using a MOSFET which supposedly handles around 200a continuous, which would be more than enough for this purpose, but evidently when the MOSFET gate isn't saturated, the resistance it creates dissipates a ton of wattage as heat. After a few seconds, the gate breaks down and the MOSFET conducts (like crazy) regardless of the absence of gate voltage.
So my question is, how do I achieve the goal of this circuit? I assume I could use multiple MOSFETs to disperse the load between them, but the overall dissipation would still be the same, which is unacceptable in a handheld device.
Could I use the rapid switching capabilities of the MOSFET to create perceived adjustable wattage at R1? Would this solve my power dissipation issues? I'm just starting to learn about gate drivers, but are they capable of varying switching times with simple input like adjusting a reference resistance via a potentiometer? Or do they always require an MCU (way beyond my capabilities) to tell them what to do? What kind of switching speed range would I need to achieve my goals?
I know I can use DC-DC converters to get similar results by adjusting the voltage at R1, but there's virtually nothing commercially available that will handle the necessary amperage and cost less than $500 or so. Hence the goal of using a comparably cheap MOSFET to control the current (rather than voltage) in a circuit that simply provides more voltage than I need.