Thank you very much, i was misunderstanding a couple of thinghs.
I've studied a little more the mosfets and i think i understand how to use them in some application now.
To be sure of that, could you confirm me that the following is a viable way of setting up a digital switch (for digital i mean it's controlled by two different input values) that must control a known load?
Im assuming the mosfet to be n-channel (V_th>0)
- Find the current needed by the LOAD, I_L (for example by current = power/voltage or things like that depending on the load, i am thinking of a lamp right now)
- Find the minimum gate voltage needed to trigger correctly the switch (allowing him not to saturate before the needed current is drawn).
In order to do this, I check the I_ds vs V_ds graph in the datasheet, and I find the first line who get to the right I_L before saturating (becoming flat, not dipendent by V_ds), and I pick the corresponding gate voltage value, V_gs. - I build a circuit like this one : http://tronixstuff.files.wordpress.com/2010/04/examp3p1.jpg.
Where of course, instead of the npn transistor i have my beloved MOSFET,the load is the relay, and in place of the digital 2 pin I have any controlled voltage supply who can furnish the V_gs value i found at point 2) - I add all the stuff not related to the transistor usage that can improve the switch, like a pull to ground resistance for the gate or other things I don't know.
OK guys, will i blow up my house, or i will switch on the lamp?
Thank you in advance