I have a simple circuit that uses a MOSFET to switch on and off a ~100W LED spotlight (30V, 3A). It works for this application.
I have been asked to modify the circuit so that the LED can be dimmed instead, but without using PWM (the reasons are beyond the scope of this question, but I can explain if needed).
So my naive solution was to drive the gate of the MOSFET with the output of a DAC, per the schematic below:
The DAC I am using is the MCP4725 (specifically the breakout board from Sparkfun). The MOSFET is a logic level one, IXFP5N50P3, and it is properly heatsinked.
After some testing with the DAC output at voltages other than 0 or 5V, I notice the MOSFET starting to fail. In some cases they end up letting some current flow even if the gate voltage is zero. In other cases they fails by never letting enough current flow for the LED to reach full brightness.
I suspect I am using the MOSFET in a mode of operation that is not safe, but I am not sure why, or how to tell by looking at the datasheet.
Is this MOSFET only usable for switching a load, and if so are there any other parts that would be suitable for this application ?