I have an n mosfet with a high side LED (between drain and 12V) and a 10 ohm from source to ground....The gate is driven by the output of an opamp which places the FET in the feedback loop. I am running this on LTSpice simulation. There is a resistor for gain tapping from the 10 ohm / source connection back to the negative input of the opamp. I am running a voltage into the positive terminal of the opamp and then monitoring Vgs, Vds and power (Vds * Is).

Somewhere along the way I have a misunderstanding.....Vds is > Vgs as seen on simulator....As an example I see Vds = 7V and Vgs is 2.5V (datasheet Vgs typ 1V , max 2.5V)...When I look at power it is a whopping 1.33W. So the questions:

Firstly Vds > Vgs means I should be in saturation mode correct?

If saturation I would have thought I could have used datasheet Rdson (0.18 ohms) and multiply by the 190mA (squared) current to get a reasonable power but when I take Vds / Id (using LTSPICE) I get Rdson of about 37 ohms. This seems to imply I am in the ohmic region . Can someone explain to me what I am missing here?

I don't seem to understand how Vds = 7V when Vgs = 2.5V and I am drawing about 190mA thru Id?

I really would like a good explanation that ties back into the Vds - Id characteristic curves for different Vgs because using that and comparing to what I see on LTSpice definitely isn't making sense.

Mosfet ZXMN3A01F

Thank you