# Why cannot I edit MOSFETs in LTspice by “nmos”

update: I edited question so that it will be mainly related to LTspice

OK, now I have used irfz44n for an example model, I realized that, by using the directive above(nmos), I am not able to modify Vto value. However if I use the second one(vdmos), I can control the Vto value. But while choosing the mosfet from component selector, I get it from "nmos" option. I wonder why this is the situation? Should I use vdmos instead of nmos all the time?

• Knowing nothing about the model, that could be perfectly reasonable. – Matt Young Dec 10 '19 at 1:52
• @MattYoung the model is ltspice default mosfet model, I am changing only the vto value. – muyustan Dec 10 '19 at 2:32
• You miss almost everything. People are not going to consult spice or guess the version or ... . Look at specs for a real world device or full specs for the LTS one, calculate what you'd expect and then comment if you find that your calculations are correct and SPICE's are wrong. – Russell McMahon Dec 10 '19 at 7:31
• @RussellMcMahon please see my edit. – muyustan Dec 10 '19 at 8:19
• IRFZ44N datasheet here At Vgs = 5V based on the datasheet I'd expects RDSon to be under 0.1 Ohm (probably worst case), so VDS a few mV. – Russell McMahon Dec 10 '19 at 9:15

Adding a .model IRFZ44N nmos(..) card will not change the type of the IRFZ44N to a monolithic mosfet.
You are therefore not able to manipulate the parameters of the IRFZ44N using .model nmos(..), but you can change them using .model vdmos(..)