vedhaanth648,
I uploaded your file for you.? It is in the Temp folder.?
BSS138.zip.
To answer your question "i dont know which one to use", use whichever one you want to use.? All three of them appear to be SPICE models, so any of them should work in SPICE (and LTspice).? Take your pick.??They appear to be MOSFET models.? Two of them can be used directly.? But one of them (BSS138.lib) is a special model that has a fourth pin for temperature.? To use that one, you will need to create (or borrow) a special MOSFET symbol that has the fourth pin, and then use that pin correctly.? That might mean connecting the fourth pin to a voltage source, or to an RC network to represent a heatsink.
So I recommend starting with the other two models first.
The other two models are ordinary 3-terminal subcircuits.? You can use them with LTspice's normal MOSFET symbols (either NMOS or PMOS as appropriate).? After adding the symbol to your schematic, then use Ctrl-right-click on the symbol, and change the Prefix value to "X" (without the quotes), and click OK.
Andy
